NCERT CBSE Standard 12 p Block Elements Chapter 7 Inorganic Chemistry

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1-Subhashish-Electrostatics-2

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Solutions to Chapter 7 :

Chalcogens-P1-O, S, Se, Te, Po-Group6A-16-ISEET, AIEEE, IIT-JEE-PU, ISc

🙂

Must see https://zookeepersblog.wordpress.com/some-points-which-i-wish-all-my-new-prospective-students-know/

🙂

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The next chapter Solution is at https://zookeepersblog.wordpress.com/ncert-cbse-standard-12-d-and-f-block-elements-chapter-8-inorganic-chemistry/
!
The previous chapter Solution is at https://zookeepersblog.wordpress.com/ncert-cbse-standard-12-general-principles-and-processes-of-isolation-of-elements-chapter-6/
!
The first Chapter Solution is at https://zookeepersblog.wordpress.com/ncert-cbse-standard-12-solid-state-chapter-1-physical-chemistry/
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Question 7.1:

Discuss the general characteristics of Group 15 elements with reference to their

electronic configuration, oxidation state, atomic size, ionisation enthalpy and

electronegativity.

Answer

General trends in group 15 elements

(i)

Electronic configuration

: All the elements in group 15 have 5 valence electrons.

Their general electronic configuration is

ns2 np3

(ii)

Oxidation states:

All these elements have 5 valence electrons and require three

more electrons to complete their octets. However, gaining electrons is very difficult as

the nucleus will have to attract three more electrons. This can take place only with

nitrogen as it is the smallest in size and the distance between the nucleus and the

valence shell is relatively small. The remaining elements of this group show a formal

oxidation state of −3 in their covalent compounds. In addition to the −3 state, N and P

also show −1 and −2 oxidation states.

All the elements present in this group show +3 and +5 oxidation states. However, the

stability of +5 oxidation state decreases down a group, whereas the stability of +3

oxidation state increases. This happens because of the inert pair effect.

(iii)

Ionization energy and electronegativity

First ionization decreases on moving down a group. This is because of increasing atomic

sizes. As we move down a group, electronegativity decreases, owing to an increase in

size.

(iv)

Atomic size:

On moving down a group, the atomic size increases. This increase in

the atomic size is attributed to an increase in the number of shells.

🙂

Group IIIA-13-P1-B,Al,Ga,In,Tl-Inorganic Chemistry
http://www.youtube.com/watch?v=PrRnCinyaio&list=PLeF13BXlaoDo3k57C7XI4jh2Wvk1ob2x5&index=30

Question 7.2:

Why does the reactivity of nitrogen differ from phosphorus?

Answer

Nitrogen is chemically less reactive. This is because of the high stability of its molecule,

N2. In N2 the two nitrogen atoms form a triple bond. This triple bond has very high bond

strength, which is very difficult to break. It is because of nitrogen’s small size that it is

able to form pπ−pπ bonds with itself. This property is not exhibited by atoms such as

phosphorus. Thus, phosphorus is more reactive than nitrogen.

🙂

Group 13-In, Tl show mixed-valence, Tl has +ve Electrode Potential-ISEET, ISc, CBSE
http://www.youtube.com/watch?v=O74xgoRE6Uc&list=PLeF13BXlaoDo3k57C7XI4jh2Wvk1ob2x5

🙂

Silica SiO2-about and Properties – Part-2-ISEET, IIT-JEE, CET, ISc, CBSE, PreUniversity
http://www.youtube.com/watch?v=FvgwW8xYPE8&list=PLeF13BXlaoDo3k57C7XI4jh2Wvk1ob2x5

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Acid Strengths in Nitrogen, Sulphur, Carbon and other Oxides-Part-6-Acids of Carbon
http://www.youtube.com/watch?v=V9w30g2FiNY&list=PLeF13BXlaoDo3k57C7XI4jh2Wvk1ob2x5&index=2

Group 4A-(14)-Carbon Family-Part-2-Ge, Uuq, Q and A, SKM Classes, ISEET, IIT-JEE-Zookeepersblog
http://www.youtube.com/watch?v=cPj1KOOlL5U&list=PLeF13BXlaoDo3k57C7XI4jh2Wvk1ob2x5&index=3

🙂

Bromine Story-uses properties
http://www.youtube.com/watch?v=Zj9mSGGwWF8&list=PLeF13BXlaoDo3k57C7XI4jh2Wvk1ob2x5

🙂

Borax-Di-Sodium-Tetra Borate-DecaWater
http://www.youtube.com/watch?v=7o1dTvFU9_k&list=PLeF13BXlaoDo3k57C7XI4jh2Wvk1ob2x5&index=17

Question 7.10 :

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Chlorine Story-ISEET,PU,ISc, CBSE, AIEEE,AIPMT
http://www.youtube.com/watch?v=5nUu6HtjHeg&list=PLeF13BXlaoDo3k57C7XI4jh2Wvk1ob2x5&index=18

🙂

Xenon Compounds various Examples
http://www.youtube.com/watch?v=1byBJYX_tNA&list=PLeF13BXlaoDo3k57C7XI4jh2Wvk1ob2x5

Question 7.14:

Why does nitrogen show catenation properties less than phosphorus?

Answer

Catenation is much more common in phosphorous compounds than in nitrogen

compounds. This is because of the relative weakness of the N−N single bond as

compared to the P−P single bond. Since nitrogen atom is smaller, there is greater

repulsion of electron density of two nitrogen atoms, thereby weakening the N−N single

bond.

Acid names of 4A and 5A Group oxides-Part-3-Various Phosphorus Acids-ISEET Bangalore
http://www.youtube.com/watch?v=GvzJVjS13N8&list=PLeF13BXlaoDo3k57C7XI4jh2Wvk1ob2x5&index=5

Question 7.15:

Give the disproportionation reaction of H3PO3

Answer

7.15-17a p-Block Standard 12 CBSE Solution

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Halogens Group 17 ( 7A )-Part-3-Dihalides, Interhalogens-ISEET, IIT-JEE, AIEEE, ISc, CBSE
http://www.youtube.com/watch?v=9F7_bn-3zrk&list=PLeF13BXlaoDo3k57C7XI4jh2Wvk1ob2x5&index=8

Question 7.18 :

Why is dioxygen a gas but sulphur a solid?

Answer

7.18-19 p-Block Standard 12 CBSE Solution

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NI3 Nitrogen triiodide can be detonaded by Alpha Radiation
http://www.youtube.com/watch?v=NwUoEgsEj2c&list=PLeF13BXlaoDo3k57C7XI4jh2Wvk1ob2x5

Question 7.20:

Which aerosols deplete ozone?

Answer

Freons or chlorofluorocarbons (CFCs) are aerosols that accelerate the depletion of ozone.

In the presence of ultraviolet radiations, molecules of CFCs break down to form chlorine:

free radicals that combine with ozone to form oxygen.

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Aluminium Oxide and Silicon Oxide do not react with water ISEET, CBSE, ISc, IIT-JEE
http://www.youtube.com/watch?v=rQAdvR5c0VQ&list=PLeF13BXlaoDo3k57C7XI4jh2Wvk1ob2x5

Question 7.21:

Describe the manufacture of H2SO4

by contact process?

Answer

Sulphuric acid is manufactured by the contact process. It involves the following steps:

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Chemical Reactivity in Group 17 elements-Part-2-ISEET, ISc, CBSE,CET,AIEEE
http://www.youtube.com/watch?v=LmCkVX276I0&list=PLeF13BXlaoDo3k57C7XI4jh2Wvk1ob2x5&index=11

Question 7.22:

How is SO2 an air pollutant?

Answer

Sulphur dioxide causes harm to the environment in many ways:

It combines with water vapour present in the atmosphere to form sulphuric acid. This

causes acid rain. Acid rain damages soil, plants, and buildings, especially those made of

marble.

Even in very low concentrations, SO2 causes irritation in the respiratory tract. It

causes throat and eye irritation and can also affect the larynx to cause breathlessness.

It is extremely harmful to plants. Plants exposed to sulphur dioxide for a long time

lose colour from their leaves. This condition is known as chlorosis. This happens because

the formation of chlorophyll is affected by the presence of sulphur dioxide.

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Gallium expands on Solidification
http://www.youtube.com/watch?v=_kfEszRfTpg&list=PLeF13BXlaoDo3k57C7XI4jh2Wvk1ob2x5

and high negative electron gain enthalpies. Therefore, they have a high tendency to gain

an electron. Hence, they act as strong oxidizing agents.

🙂

Group IIIA-13-P1-B,Al,Ga,In,Tl-Inorganic Chemistry
http://www.youtube.com/watch?v=PrRnCinyaio&list=PLeF13BXlaoDo3k57C7XI4jh2Wvk1ob2x5&index=14

Question 7.24:

Explain why fluorine forms only one oxoacid, HOF.

Answer

Fluorine forms only one oxoacid i.e., HOF because of its high electronegativity and small

size.

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Group IVA-14-P1-C,Si,Ge, Sn,Pb-Zintl Ions
http://www.youtube.com/watch?v=5TDWdf_leUs&list=PLeF13BXlaoDo3k57C7XI4jh2Wvk1ob2x5&index=15

Question 7.25:

Explain why inspite of nearly the same electronegativity, oxygen forms hydrogen

bonding while chlorine does not.

Answer

Both chlorine and oxygen have almost the same electronegativity values, but chlorine

rarely forms hydrogen bonding. This is because in comparison to chlorine, oxygen has a

smaller size and as a result, a higher electron density per unit volume.

🙂

Litharge is a natural mineral of Lead(II) oxide-ISEET,ISc,PU,AIEEE
http://www.youtube.com/watch?v=PIyCqutZVjA&list=PLeF13BXlaoDo3k57C7XI4jh2Wvk1ob2x5

🙂

Question 7.28

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Acid names of 4A and 5A Group oxides-Part-3-Various Phosphorus Acids-ISEET Bangalore
http://www.youtube.com/watch?v=GvzJVjS13N8&list=PLeF13BXlaoDo3k57C7XI4jh2Wvk1ob2x5&index=21

🙂
Group 4A-(14)-Carbon Family-Part-2-Ge, Uuq, Q and A, SKM Classes, ISEET, IIT-JEE-Zookeepersblog
http://www.youtube.com/watch?v=cPj1KOOlL5U&list=PLeF13BXlaoDo3k57C7XI4jh2Wvk1ob2x5&index=24

Some Questions :

1. PCl3 fumes in moist air. Why? 1

2. Oxides of P, As, Sb exist as dimers (P4O6, P4O10, As4O6, and As4O10). Why? 1

3. P4O10 is used as dehydrating agent. Why? 1

4. Oxygen and sulphur exhibit –2 oxidation state where as others (Se, Te) exhibit +2

oxidation states. 1

5. Chemical methods are not practicable for the preparation of Fluorine. 1

6. Why H2SO4 is not used for the preparation of HBr from NaBr 1

7. Iodine forms I3

– ion but F2 does not form F3

– ion. Why? 1

8. NH3 has a higher proton affinity than PH3. Explain 1

9. Bleaching of flowers by chlorine is permanent while that by sulphur dioxide is temporary. Why? 1

10. Why does chlorine water loses its yellow colour on standing? 1

2 – MARKS QUESTIONS

11. Oxides of Nitrogen have open chain structure while those of phosphorous have closed chain or cage structure. Why is it so? Illustrate with one structural example for each type of oxide or the oxides of phosphorous have cage structure but not open ones. 2

12. When a moist blue litmus paper is dipped in a solution of hypochlorous acid, it first turns red and then latter gets decolorized. Why? 2

13. Iodine is liberated when KI is added to a solution of Cu2+ ions but Cl2 is not liberated when KCl is added to a solution of Cu2+ ions. Why? Explain. 2

14. State the reasons

i. ClF3 exists but FCl3 does not

ii. BH4

– and NH4

+ are isoloble 2

15. Why is it important to add KF in HF and exclude moisture during electrolysis of HF for the preparation of Fluorine ? 2

16. Why SO2 is a better reducing agent in alkaline medium as compared to that in acidic medium ? Explain.

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Q. Discuss the general characteristics of Group 15 elements with reference to their electronic configuration, oxidation state, atomic size, ionisation enthalpy and electronegativities

Answer

General characteristics of group 15 elements are:

a) Electronic configuration
Elements of group 15 have 5 valence electrons. Their general electronic configuration is ns² np³.

b) Ionization energy
On moving down a group, first ionization energy decreases. This happens because of increasing atomic sizes.

c) Electronegativity
On moving down a group, electronegativity decreases

d) Oxidation states
Elements of this group have 5 valence electrons and they require three more electrons to complete their octets. But, gaining electrons is very difficult in nitrogen as the nucleus will have to attract three more electrons. The remaining elements of this group show oxidation state of −3. In addition to the −3 state, N and P also show −1 & −2 oxidation states.

All the elements present in this group show +3 and +5 oxidation states. However, the stability of +5 oxidation state decreases down a group, whereas the stability of +3 oxidation state increases. This happens because of the inert pair effect.

e) Atomic size:
On moving down a group, atomic size increases. This happens because of increase in the number of shells.

Q. Why does the reactivity of nitrogen differ from phosphorus?

Answer

Electronic configuration of nitrogen is half filled & we know that fully filled & partially filled orbitals are quiet stable. Being, smaller in size, nitrogen is chemically less reactive. Whereas when we move down the group, size of atom increases, thus, other elements of this group do not exhibit this property. As size increases, effective nuclear charge of atom decreases & it can lose & gain electrons easily & show reactivity towards other elements. Thus, phosphorus is more reactive than nitrogen.

Q. Discuss the trends in chemical reactivity of group 15 elements.

Answer

General trends in chemical properties of group – 15

a) Reactivity towards hydrogen:
Group 15 elements react with hydrogen & form hydrides having formula EH3, where E = N, P, As, Sb, or Bi. The stability of hydrides decreases on moving down from NH3 to BiH3.

b) Reactivity towards oxygen:
Group 15 elements form two types of oxides: E2O3 and E2O5, where E = N, P, As, Sb, or Bi. The oxides having higher oxidation state are more acidic than the other. However, the acidic character decreases on moving down a group.

c) Reactivity towards halogens:
The group 15 elements react with halogens to form two types of salts: EX3 and EX5. But, nitrogen does not form NX5 as d-orbitals are absent in it.

d) Reactivity towards metals:
On reaction with metals, group 15 elements form binary compounds in which metals exhibit −3 oxidation states.

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Chemical Reactivity in Group 17 elements-Part-2-ISEET, ISc, CBSE,CET,AIEEE
http://www.youtube.com/watch?v=LmCkVX276I0&list=PLeF13BXlaoDo3k57C7XI4jh2Wvk1ob2x5&index=26

🙂

sulphur Trioxide-SO3-ISEET-PU-ISc-CBSE-School-College-Inorganic Chemistry
http://www.youtube.com/watch?v=tSIqtmhm63E&list=PLeF13BXlaoDo3k57C7XI4jh2Wvk1ob2x5

🙂

Halogens Group 17 ( 7A )-Part-3-Dihalides, Interhalogens-ISEET, IIT-JEE, AIEEE, ISc, CBSE
http://www.youtube.com/watch?v=9F7_bn-3zrk&list=PLeF13BXlaoDo3k57C7XI4jh2Wvk1ob2x5&index=27

🙂

Group IVA-14-P1-C,Si,Ge, Sn,Pb-Zintl Ions
http://www.youtube.com/watch?v=5TDWdf_leUs&list=PLeF13BXlaoDo3k57C7XI4jh2Wvk1ob2x5&index=29

🙂

Anahydride of Nitrous acid
http://www.youtube.com/watch?v=UFWyVE9iK-o&list=PLeF13BXlaoDo3k57C7XI4jh2Wvk1ob2x5

🙂

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SKM Classes Bangalore for ISEET Group 2A Alkaline Earth Metals-Be, Mg, Ca, Sr, Ba, Ra-Part-2
http://www.youtube.com/watch?v=aI-oS0ct4Xk&list=PLeF13BXlaoDpHRz923RxO0-08I2JLLEBD&index=29

🙂

S-Block Elements 1A 2A Explained in detail with 8 types of periodic tables Inorganic Chemistry-P1
http://www.youtube.com/watch?v=e0HZVjew3Qc&list=PLeF13BXlaoDpHRz923RxO0-08I2JLLEBD&index=47

🙂

Alkaline Earths Group 2A Be, Mg, Ca, Sr, Ba, Ra-Part-3-Hard water, Abundance
http://www.youtube.com/watch?v=1HhvnWUEwg8&list=PLeF13BXlaoDpHRz923RxO0-08I2JLLEBD&index=44

Alkali Metals Group 1A-Part-3-Solvay process, Alkali, Reactions-ISEET, ISc, CBSE
http://www.youtube.com/watch?v=Ym_Ue8g_s10&list=PLeF13BXlaoDpHRz923RxO0-08I2JLLEBD&index=43

🙂

S-Block Elements 1A 2A Explained in detail with 8 types of periodic tables Inorganic Chemistry-P1
http://www.youtube.com/watch?v=e0HZVjew3Qc&list=PLeF13BXlaoDpHRz923RxO0-08I2JLLEBD&index=15

Question 7.39:

Why do noble gases have comparatively large atomic sizes?

Answer

Noble gases do not form molecules. In case of noble gases, the atomic radii corresponds

to van der Waal’s radii. On the other hand, the atomic radii of other elements correspond

to their covalent radii. By definition, van der Waal’s radii are larger than covalent radii. It

is for this reason that noble gases are very large in size as compared to other atoms

belonging to the same period.

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Alkali and alkaline earth metals-Part-6-Anomalous behavior of beryllium-ISEET, ISc, CBSE
http://www.youtube.com/watch?v=soqub8Nc3rY&list=PLeF13BXlaoDpHRz923RxO0-08I2JLLEBD&index=23

Question 7.40:

List the uses of Neon and argon gases.

Answer

Uses of neon gas:

(i)

It is mixed with helium to protect electrical equipments from high voltage.

(ii)

It is filled in discharge tubes with characteristic colours.

(iii)

It is used in beacon lights.

Uses of Argon gas:

(i)

Argon along with nitrogen is used in gas:filled electric lamps. This is because Ar is

more inert than N.

(ii)

It is usually used to provide an inert temperature in a high metallurgical process.

(iii)

It is also used in laboratories to handle air:sensitive substances.

🙂

Alkaline Earths Group 2A Be, Mg, Ca, Sr, Ba, Ra-Part-3-Hard water, Abundance
http://www.youtube.com/watch?v=1HhvnWUEwg8&list=PLeF13BXlaoDpHRz923RxO0-08I2JLLEBD&index=12

text Question 7.1:

Why are pentahalides more covalent than trihalides?

Answer

In pentahalides, the oxidation state is +5 and in trihalides, the oxidation state is +3.

Since the metal ion with a high charge has more polarizing power, pentahalides are

more covalent than trihalides.

Alkali Metals Group 1A-Part-3-Solvay process, Alkali, Reactions-ISEET, ISc, CBSE
http://www.youtube.com/watch?v=Ym_Ue8g_s10&list=PLeF13BXlaoDpHRz923RxO0-08I2JLLEBD&index=20

text Question 7.2 :

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Alkali and alkaline earth metals-Part-7-DIAGONAL SIMILARITY Beryllium, Aluminum
http://www.youtube.com/watch?v=2nEinJZI1wo&list=PLeF13BXlaoDpHRz923RxO0-08I2JLLEBD

Text Question 7.3:

Why is N2 less reactive at room temperature?

Answer

The two N atoms in N2 are bonded to each other by very strong triple covalent bonds.

The bond dissociation energy of this bond is very high. As a result, N2 is less reactive at room temperature.

Alkali and alkaline earth metals-Part-3-Castner kellner cell-ISEET, ISc, CBSE
http://www.youtube.com/watch?v=aWK8WEWEEtc&list=PLeF13BXlaoDpHRz923RxO0-08I2JLLEBD&index=32

Question 7.4:

Mention the conditions required to maximise the yield of ammonia.

Answer

Ammonia is prepared using the Haber’s process. The yield of ammonia can be maximized

under the following conditions:

7.4b txt p-Block Standard 12 CBSE Solution

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S-Block Elements 1A 2A Explained in detail with 8 types of periodic tables Inorganic Chemistry-P3
http://www.youtube.com/watch?v=9NDG4Zf_qeY&list=PLeF13BXlaoDpHRz923RxO0-08I2JLLEBD

🙂

7.5 txt p-Block Standard 12 CBSE Solution

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Alkali and alkaline earth metals-Part-4-Kellner-Solvay cell-ISEET, ISc, CBSE
http://www.youtube.com/watch?v=80cQVG7jXrg&list=PLeF13BXlaoDpHRz923RxO0-08I2JLLEBD&index=26

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Alkali and alkaline earth metals-Part-2-Gossage process for NaOH-ISEET, ISc, CBSE
http://www.youtube.com/watch?v=ulCQG0oRyv0&list=PLeF13BXlaoDpHRz923RxO0-08I2JLLEBD&index=11

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Alkali Metals Group 1A-Part-3-Solvay process, Alkali, Reactions-ISEET, ISc, CBSE
http://www.youtube.com/watch?v=Ym_Ue8g_s10&list=PLeF13BXlaoDpHRz923RxO0-08I2JLLEBD&index=41

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Alkali metals Notes Group 1A-NaOH absorbs H2O, CO2 so standard solution difficult
http://www.youtube.com/watch?v=0gn7b6IKwiY&list=PLeF13BXlaoDpHRz923RxO0-08I2JLLEBD&index=35

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S Block Elements Notes and important points-Part-2-ISEET, IIT-JEE, CET, ISc, CBSE, PU
http://www.youtube.com/watch?v=hPm_m21BR9U&list=PLeF13BXlaoDpHRz923RxO0-08I2JLLEBD&index=2

🙂

Alkaline Earths Group 2A Be, Mg, Ca, Sr, Ba, Ra-Part-3-Hard water, Abundance
http://www.youtube.com/watch?v=1HhvnWUEwg8&list=PLeF13BXlaoDpHRz923RxO0-08I2JLLEBD&index=44

🙂
Alkali Metals Group 1A-Part-3-Solvay process, Alkali, Reactions-ISEET, ISc, CBSE
http://www.youtube.com/watch?v=Ym_Ue8g_s10&list=PLeF13BXlaoDpHRz923RxO0-08I2JLLEBD&index=22

🙂

Caesium has 2 melting points, Rubidium Uses and properties 1A Group Alkaline Metals S Block
http://www.youtube.com/watch?v=aOXAYx529bg&list=PLeF13BXlaoDpHRz923RxO0-08I2JLLEBD&index=38

🙂
S-Block Elements 1A 2A Explained in detail with 8 types of periodic tables Inorganic Chemistry-P2
http://www.youtube.com/watch?v=oTDiH7OsLOY&list=PLeF13BXlaoDpHRz923RxO0-08I2JLLEBD&index=3

Question 7.14:

Write the order of thermal stability of the hydrides of Group 16 elements.

Answer

The thermal stability of hydrides decreases on moving down the group. This is due to a

decrease in the bond dissociation enthalpy (H−E) of hydrides on moving down the

group.

7.14b txt p-Block Standard 12 CBSE Solution

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Alkali metals Notes Group 1A-NaOH absorbs H2O, CO2 so standard solution difficult
http://www.youtube.com/watch?v=0gn7b6IKwiY&list=PLeF13BXlaoDpHRz923RxO0-08I2JLLEBD&index=37

🙂
S-Block Elements 1A 2A Explained in detail with 8 types of periodic tables Inorganic Chemistry-P2
http://www.youtube.com/watch?v=oTDiH7OsLOY&list=PLeF13BXlaoDpHRz923RxO0-08I2JLLEBD&index=5

Question 7.16:

Which of the following does not react with oxygen directly?

Zn, Ti, Pt, Fe

Answer

Pt is a noble metal and does not react very easily. All other elements, Zn, Ti, Fe, are

quite reactive. Hence, oxygen does not react with platinum (Pt) directly.

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Be(Beryllium), Nb(Niobium), Tantalum-Part-2
http://www.youtube.com/watch?v=xv1WLLmHFtg&list=PLeF13BXlaoDpHRz923RxO0-08I2JLLEBD&index=8

🙂

7.17a txt p-Block Standard 12 CBSE Solution

7.17b txt p-Block Standard 12 CBSE Solution

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Alkali and alkaline earth metals-Part-2-Gossage process for NaOH-ISEET, ISc, CBSE
http://www.youtube.com/watch?v=ulCQG0oRyv0&list=PLeF13BXlaoDpHRz923RxO0-08I2JLLEBD&index=9

🙂

7.18 txt p-Block Standard 12 CBSE Solution

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Alkaline Earths Group 2A Be, Mg, Ca, Sr, Ba, Ra-Part-3-Hard water, Abundance
http://www.youtube.com/watch?v=1HhvnWUEwg8&list=PLeF13BXlaoDpHRz923RxO0-08I2JLLEBD&index=12

🙂
Alkali and alkaline earth metals-Part-4-Kellner-Solvay cell-ISEET, ISc, CBSE
http://www.youtube.com/watch?v=80cQVG7jXrg&list=PLeF13BXlaoDpHRz923RxO0-08I2JLLEBD&index=28

Question 7.20 Text :

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Why does NH3 form hydrogen bond but PH3 does not?

Answer

Nitrogen is highly electronegative as compared to phosphorus. This causes a greater attraction of electrons towards nitrogen in NH3 than towards phosphorus in PH3. Hence, the extent of hydrogen bonding in PH3 is very less as compared to NH3.

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Question 7.26:

Considering the parameters such as bond dissociation enthalpy, electron gain enthalpy

and hydration enthalpy, compare the oxidising power of F2

and Cl2

Answer

Fluorine is a much stronger oxidizing agent than chlorine. The oxidizing power depends

on three factors.

Bond dissociation energy

Electron gain enthalpy

Hydration enthalpy

The electron gain enthalpy of chlorine is more negative than that of fluorine. However,

the bond dissociation energy of fluorine is much lesser than that of chlorine. Also,

because of its small size, the hydration energy of fluorine is much higher than that of

chlorine. Therefore, the latter two factors more than compensate for the less negative

electron gain enthalpy of fluorine. Thus, fluorine is a much stronger oxidizing agent than

chlorine.

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Question 7.27:

Give two examples to show the anomalous behaviour of fluorine.

Answer

Anomalous behaviour of fluorine

(i)

It forms only one oxoacid as compared to other halogens that form a number of

oxoacids.

(ii)

Ionisation enthalpy, electronegativity, and electrode potential of fluorine are much

higher than expected.

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Question 7.28:

Sea is the greatest source of some halogens. Comment.

Answer

7.29 txt p-Block Standard 12 CBSE Solution

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7.30 txt p-Block Standard 12 CBSE Solution

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7.31 txt p-Block Standard 12 CBSE Solution

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Question 7.32:

Why is helium used in diving apparatus?

Answer

Air contains a large amount of nitrogen and the solubility of gases in liquids increases

with increase in pressure. When sea divers dive deep into the sea, large amount of

nitrogen dissolves in their blood. When they come back to the surface, solubility of

nitrogen decreases and it separates from the blood and forms small air bubbles. This

leads to a dangerous medical condition called bends. Therefore, air in oxygen cylinders

used for diving is diluted with helium gas. This is done as He is sparingly less soluble in

blood.

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7.33 txt p-Block Standard 12 CBSE Solution

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Question 7.34:

Why has it been difficult to study the chemistry of radon?

Answer

It is difficult to study the chemistry of radon because it is a radioactive substance having

a half:life of only 3.82 days. Also, compounds of radon such as RnF2

have not been isolated. They have only been identified.

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Diversity in chemistry is the hallmark of p–block elements manifested in their ability to react with the elements of s–, d– and f–blocks as well as with their own.

In Class XI, you have learnt that the p-block elements are placed in groups 13 to 18 of the periodic table. Their valence shell electronic configuration is ns²np^1–6 (except He which has 1s configuration). The properties of p-block elements like that of others are greatly influenced by atomic sizes, ionisation enthalpy, electron gain enthalpy and electronegativity. The absence of d- orbitals in second period and presence of d or d and f orbitals in heavier elements (starting from third period onwards) have significant effects on the properties of elements. In addition, the presence of all the three types of elements; metals, metalloids and non-metals bring diversification in chemistry of these elements.

Having learnt the chemistry of elements of Groups 13 and 14 of the p-block of periodic table in Class XI, you will learn the chemistry of the elements of subsequent groups in this Unit.

7.1 Group 15 Elements

Group 15 includes nitrogen, phosphorus, arsenic, antimony and bismuth. As we go down the group, there is a shift from non-metallic to metallic through metalloidic character. Nitrogen and phosphorus are non-metals, arsenic and antimony metalloids and bismuth is a typical metal.

7.1.1 Occurrence

Molecular nitrogen comprises 78% by volume of the atmosphere. In the earth’s crust, it occurs as sodium nitrate, NaNO₃ (called Chile saltpetre) and potassium nitrate (Indian saltpetre). It is found in the form of proteins in plants and animals. Phosphorus occurs in minerals of the apatite family, Ca₉(PO₄)₆. CaX₂ (X = F, Cl or OH) (e.g., fluorapatite Ca₉(PO₄)₆.CaF₂) which are the main components of phosphate rocks. Phosphorus is an essential constituent of animal and plant matter. It is present in bones as well as in living cells. Phosphoproteins are present in milk and eggs. Arsenic, antimony and bismuth are found mainly as sulphide minerals.

The important atomic and physical properties of this group elements along with their electronic configurations are given in Table 7.1. Trends of some of the atomic, physical and chemical properties of the group are discussed below.

Table 7.1: Atomic and Physical Properties of Group 15 Elements
Property	N	P	As	Sb	Bi
Atomic number	7	15	33	51	83
Atomic mass/g mol^-1	14.01	30.97	74.92	121.75	208.98
Electronic configuration	[He]2S²2p³	[Ne]3S²2p³	[Ar]3d¹⁰4s²4p³	[Kr]4d¹⁰5s²5p³	[Xe]4f¹⁴5d¹⁰6s²6p³
Ionisation I enthalpy II (Δ_iH/(kj III mol^-1)	1402 2856 4577	1012 1903 2910	947 1798 2736	834 1595 1610	703 1610 2466
Electronegetivity	3.0	2.1	2.0	1.9	1.9
Covalent radius/pm^a	70	110	121	141	148
Ionic radius/pm	171^b	212^b	222^b	76^c	103^c
Melting point/K	63*	317^d	1089^e	904	544
Boiling point/K	77.2*	554^d	888^f	1860	1837
Density/[g cm^-3(298 K)]	0.879^g	1.823	5.778^h	6.697	9.808

Trends of some of the atomic, physical and chemical properties of the group are discussed below.

7.1.2 Electronic Configuration

The valence shell electronic configuration of these elements is ns²np³. The s orbital in these elements is completely filled and p orbitals are half-filled, making their electronic configuration extra stable.

7.1.3 Atomic and Ionic Radii

Covalent and ionic (in a particular state) radii increase in size down the group. There is a considerable increase in covalent radius from N to P. However, from As to Bi only a small increase in covalent radius is observed. This is due to the presence of completely filled d and/or f orbitals in heavier members.

7.1.4 Ionisation Enthalpy

Ionisation enthalpy decreases down the group due to gradual increase in atomic size. Because of the extra stable half-filled p orbitals electronic configuration and smaller size, the ionisation enthalpy of the group 15 elements is much greater than that of group 14 elements in the corresponding periods. The order of successive ionisation enthalpies, as expected is Δ_iH₁ Δ_iH₂ Δ_iH₃ (Table 7.1).

7.1.5 Electronegativity

The electronegativity value, in general, decreases down the group with increasing atomic size. However, amongst the heavier elements, the difference is not that much pronounced.

7.1.6 Physical Properties

All the elements of this group are polyatomic. Dinitrogen is a diatomic gas while all others are solids. Metallic character increases down the group. Nitrogen and phosphorus are non-metals, arsenic and antimony metalloids and bismuth is a metal. This is due to decrease in ionisation enthalpy and increase in atomic size. The boiling points, in general, increase from top to bottom in the group but the melting point increases upto arsenic and then decreases upto bismuth. Except nitrogen, all the elements show allotropy.

7.1.7 Chemical Properties

Oxidation states and trends in chemical reactivity

The common oxidation states of these elements are –3, +3 and +5. The tendency to exhibit –3 oxidation state decreases down the group due to increase in size and metallic character. In fact last member of the group, bismuth hardly forms any compound in –3 oxidation state. The stability of +5 oxidation state decreases down the group. The only well characterised Bi (V) compound is BiF₅. The stability of +5 oxidation state decreases and that of +3 state increases (due to inert pair effect) down the group. Nitrogen exhibits + 1, + 2, + 4 oxidation states also when it reacts with oxygen. Phosphorus also shows +1 and +4 oxidation states in some oxoacids.

In the case of nitrogen, all oxidation states from +1 to +4 tend to disproportionate in acid solution. For example,
3HNO₂ → HNO₃ + H₂O + 2NO

Similarly, in case of phosphorus nearly all intermediate oxidation states disproportionate into +5 and –3 both in alkali and acid. However +3 oxidation state in case of arsenic, antimony and bismuth becomes increasingly stable with respect to disproportionation.

Nitrogen is restricted to a maximum covalency of 4 since only four (one s and three p) orbitals are available for bonding. The heavier elements have vacant d orbitals in the outermost shell which can be used for bonding (covalency) and hence, expand their covalence as in PF⁻₆.

Anomalous properties of nitrogen

Nitrogen differs from the rest of the members of this group due to its small size, high electronegativity, high ionisation enthalpy and non-availability of d orbitals. Nitrogen has unique ability to form pπ -p π multiple bonds with itself and with other elements having small size and high electronegativity (e.g., C, O). Heavier elements of this group do not form p π -pπ bonds as their atomic orbitals are so large and diffuse that they cannot have effective overlapping. Thus, nitrogen exists as a diatomic molecule with a triple bond (one s and two p) between the two atoms. Consequently, its bond enthalpy (941.4 kJ mol^–1 ) is very high. On the contrary, phosphorus, arsenic and antimony form single bonds as P–P, As–As and Sb–Sb while bismuth forms metallic bonds in elemental state. However, the single N–N bond is weaker than the single P–P bond because of high interelectronic repulsion of the non-bonding electrons, owing to the small bond length. As a result the catenation tendency is weaker in nitrogen. Another factor which affects the chemistry of nitrogen is the absence of d orbitals in its valence shell. Besides restricting its covalency to four, nitrogen cannot form dπ –pπ bond as the heavier elements can e.g., R₃P = O or R₃P = CH₂ (R = alkyl group). Phosphorus and arsenic can form dπ –dπ bond also with transition metals when their compounds like P(C₂H₅)₃ and As(C₆H₅)₃ act as ligands.
(i) Reactivity towards hydrogen: All the elements of Group 15 form hydrides of the type EH3 where E = N, P, As, Sb or Bi. Some of the properties of these hydrides are shown in Table 7.2. The hydrides show regular gradation in their properties. The stability of hydrides decreases from NH₃ to BiH₃ which can be observed from their bond dissociation enthalpy. Consequently, the reducing character of the hydrides increases. Ammonia is only a mild reducing agent while BiH₃ is the strongest reducing agent amongst all the hydrides. Basicity also decreases in the order NH₃ > PH₃ > AsH₃ > SbH₃ > BiH₃.

Table 7.2: Properties of Hydrides of Group 15 Elements
Property	NH₃	PH₃	AsH₃	SbH₃	BiH₃
Melting point/K	195.2	139.5	156.7	185	–
Boiling point/K	238.5	185.5	210.6	254.6	290
(E-H) Distance/pm	101.7	141.9	151.9	170.7	–
HEH angle ()	107.8	93.6	91.8	91.3	–
Δ_fH^v/kj mol^-1	-46.1	13.4	66.4	145.1	278
Δ_dissH^v(E-H)/kj mol^-1	389	322	297	255	–

(ii) Reactivity towards oxygen: All these elements form two types of oxides: E₂O₃ and E₂O₅. The oxide in the higher oxidation state of the element is more acidic than that of lower oxidation state. Their acidic character decreases down the group. The oxides of the type E₂O₃ of nitrogen and phosphorus are purely acidic, that of arsenic and antimony amphoteric and those of bismuth predominantly basic.

(iii) Reactivity towards halogens: These elements react to form two series of halides: EX₃ and EX₅. Nitrogen does not form pentahalide due to non-availability of the d orbitals in its valence shell. Pentahalides are more covalent than trihalides. All the trihalides of these elements except those of nitrogen are stable. In case of nitrogen, only NF₃ is known to be stable. Trihalides except BiF₃ are predominantly covalent in nature.

(iv) Reactivity towards metals: All these elements react with metals to form their binary compounds exhibiting –3 oxidation state, such as, Ca₃N₂ (calcium nitride) Ca₃P₂ (calcium phosphide), Na₃As₂ (sodium arsenide), Zn₃Sb₂ (zinc antimonide) and Mg₃Bi₂ (magnesium bismuthide).

Example 7.1
Though nitrogen exhibits +5 oxidation state, it does not form pentahalide. Give reason.
Solution
Nitrogen with n = 2, has s and p orbitals only. It does not have d orbitals to expand its covalence beyond four. That is why it does not form pentahalide.

Example 7.2
PH₃ has lower boiling point than NH₃. Why?
Solution
Unlike NH₃, PH₃ molecules are not associated through hydrogen bonding in liquid state. That is why the boiling point of PH₃ is lower than NH₃.

Intext Questions
7.1 Why are pentahalides more covalent than trihalides ?
7.2 Why is BiH₃ the strongest reducing agent amongst all the hydrides of Group 15 elements?

7.2 Dinitrogen
Preparation
Dinitrogen is produced commercially by the liquefaction and fractional distillation of air. Liquid dinitrogen (b.p. 77.2 K) distils out first leaving behind liquid oxygen (b.p. 90 K).
In the laboratory, dinitrogen is prepared by treating an aqueous solution of ammonium chloride with sodium nitrite.
NH₄CI(aq) + NaNO₂(aq) → N₂(g) + 2H₂O(l) + NaCl (aq)
Small amounts of NO and HNO₃ are also formed in this reaction; these impurities can be removed by passing the gas through aqueous sulphuric acid containing potassium dichromate. It can also be obtained by the thermal decomposition of ammonium dichromate.

Very pure nitrogen can be obtained by the thermal decomposition of sodium or barium azide.
Ba(N₃)₂ → Ba + 3N₂

Properties
Dinitrogen is a colourless, odourless, tasteless and non-toxic gas. Nitrogen atom has two stable isotopes: ¹⁴N and ₁₅N. It has a very low solubility in water (23.2 cm per litre of water at 273 K and 1 bar pressure) and low freezing and boiling points (Table 7.1).

Dinitrogen is rather inert at room temperature because of the high bond enthalpy of N ≡N bond. Reactivity, however, increases rapidly with rise in temperature. At higher temperatures, it directly combines with some metals to form predominantly ionic nitrides and with non-metals, covalent nitrides. A few typical reactions are:

It combines with hydrogen at about 773 K in the presence of a catalyst (Haber’s Process) to form ammonia:

Dinitrogen combines with dioxygen only at very high temperature (at about 2000 K) to form nitric oxide, NO.

Uses: The main use of dinitrogen is in the manufacture of ammonia and other industrial chemicals containing nitrogen, (e.g., calcium cyanamide). It also finds use where an inert atmosphere is required (e.g., in iron and steel industry, inert diluent for reactive chemicals). Liquid dinitrogen is used as a refrigerant to preserve biological materials, food items and in cryosurgery.

Example 7.3 Write the reaction of thermal decomposition of sodium azide.
Solution
Thermal decomposition of sodium azide gives dinitrogen gas.
2NaN₃ → 2Na + 3N₂

Intext Question
7.3 Why is N₂ less reactive at room temperature?

7.3 Ammonia Preparation
Ammonia is present in small quantities in air and soil where it is formed by the decay of nitrogenous organic matter e.g., urea.
NH₂ CONH₂ + 2H₂O → ( NH₄ )₂CO₃
2NH₃ + H₂O + CO₂

On a small scale ammonia is obtained from ammonium salts which decompose when treated with caustic soda or lime.
2NH₄Cl + Ca(OH)₂ → 2NH₃ + 2H₂O + CaCl₂
(NH₄)₂ SO₄ + 2NaOH → 2NH₃ + 2H₂O + Na₂SO₄

On a large scale, ammonia is manufactured by Haber’s process.

N₂(g) + 3H₂(g) ‡ 2NH₃(g); Δ_fH° = – 46.1 kJ mol⁻¹

In accordance with Le Chatelier’s principle, high pressure would favour the formation of ammonia. The optimum conditions for the production of ammonia are a pressure of 200 × 10⁵ Pa (about 200 atm), a temperature of ~ 700 K and the use of a catalyst such as iron oxide with small amounts of K₂O and Al₂O₃ to increase the rate of attainment of equilibrium. The flow chart for the production of ammonia is shown in Fig. 7.1. Earlier, iron was used as a catalyst with molybdenum as a promoter.

Properties

Ammonia is a colourless gas with a pungent odour. Its freezing and boiling points are 198.4 and 239.7 K respectively. In the solid and liquid states, it is associated through hydrogen bonds as in the case of water and that accounts for its higher melting and boiling points than expected on the basis of its molecular mass. The ammonia molecule is trigonal pyramidal with the nitrogen atom at the apex. It has three bond pairs and one lone pair of electrons as shown in the structure.
Ammonia gas is highly soluble in water. Its aqueous solution is weakly basic due to the formation of OH⁻ ions.
NH₃(g) + H₂O(l) l NH₄⁺ (aq) + OH⁻ (aq)

It forms ammonium salts with acids, e.g., NH₄Cl, (NH₄)₂ SO₄, etc. As a weak base, it precipitates the hydroxides (hydrated oxides in case of some metals) of many metals from their salt solutions. For example,
ZnSO₄ ( aq ) + 2NH₄OH ( aq ) → Zn(OH)₂ ( s ) + ( NH₄)₂ SO₄ ( aq )
( white ppt )
FeCl₃(aq) + NH₄OH ( aq ) → Fe₂O₃ .xH₂O ( s ) + NH₄Cl ( aq )
( brown ppt )

The presence of a lone pair of electrons on the nitrogen atom of the ammonia molecule makes it a Lewis base. It donates the electron pair and forms linkage with metal ions and the formation of such complex compounds finds applications in detection of metal ions such as Cu²⁺ , Ag⁺ :
Cu²⁺(aq) + 4NH₃(aq) ‡ [Cu(NH₃)₄]²⁺ (aq)
(blue) (deep blue)
Ag⁺(aq) + Cl⁻ ( aq ) → AgCl ( s )
(colourless) (white ppt)

AgCl ( s ) + 2NH₃ ( aq ) → Ag ( NH₃ )₂Cl ( aq )
(white ppt) (colourless)

Uses: Ammonia is used to produce various nitrogenous fertilisers (ammonium nitrate, urea, ammonium phosphate and ammonium sulphate) and in the manufacture of some inorganic nitrogen compounds, the most important one being nitric acid. Liquid ammonia is also used as a refrigerant.

Example 7.4
Why does NH₃ act as a Lewis base ?
Solution
Nitrogen atom in NH₃ has one lone pair of electrons which is available for donation. Therefore, it acts as a Lewis base.

Intext Questions
7.4 Mention the conditions required to maximise the yield of ammonia.
7.5 How does ammonia react with a solution of Cu²⁺ ?

7.4 Oxides of Nitrogen

Nitrogen forms a number of oxides in different oxidation states. The names, formulas, preparation and physical appearance of these oxides are given in Table 7.3.

Lewis dot main resonance structures and bond parameters of oxides are given in Table 7.4.

Example 7.5
Why does NO₂ dimerise?
Solution
NO₂ contains odd number of valence electrons. It behaves as a typical odd molecule. On dimerisation, it is converted to stable N₂O₄ molecule with even number of electrons.

Intext Question
7.6 What is the covalence of nitrogen in N₂O₅ ?

7.5 Nitric Acid

Nitrogen forms oxoacids such as H₂N₂O₂ (hyponitrous acid), HNO₂ (nitrous acid) and HNO₃ (nitric acid). Amongst them HNO₃ is the most important.

Preparation

In the laboratory, nitric acid is prepared by heating KNO₃ or NaNO₃ and concentrated H₂SO₄ in a glass retort.
NaNO₃ + H₂SO₄ → NaHSO₄ + HNO₃
On a large scale it is prepared mainly by Ostwald’s process. This method is based upon catalytic oxidation of NH₃ by atmospheric oxygen.

Nitric oxide thus formed combines with oxygen giving NO₂.
2NO ( g ) + O₂ ( g )→2NO₂ ( g )

Nitrogen dioxide so formed, dissolves in water to give HNO₃.
3NO₂ ( g ) + H₂O ( l ) → 2HNO₃ ( aq ) + NO ( g )

NO thus formed is recycled and the aqueous HNO₃ can be concentrated by distillation upto ~ 68% by mass. Further concentration to 98% can be achieved by dehydration with concentrated H₂SO₄.

Properties

It is a colourless liquid (f.p. 231.4 K and b.p. 355.6 K). Laboratory grade nitric acid contains ~ 68% of the HNO₃ by mass and has a specific gravity of 1.504.
In the gaseous state, HNO₃ exists as a planar molecule with the structure as shown.
In aqueous solution, nitric acid behaves as a strong acid giving hydronium and nitrate ions.
HNO₃(aq) + H₂O(l) → H₃O⁺ (aq) + NO₃^– (aq)
Concentrated nitric acid is a strong oxidising agent and attacks most metals except noble metals such as gold and platinum. The products of oxidation depend upon the concentration of the acid, temperature and the nature of the material undergoing oxidation.

3Cu + 8 HNO₃(dilute) → 3Cu(NO₃)₂ + 2NO + 4H₂O
Cu + 4HNO₃(conc.) → Cu(NO₃)₂ + 2NO₂ + 2H₂O

Zinc reacts with dilute nitric acid to give N2O and with concentrated acid to give NO₂.

4Zn + 10HNO₃(dilute) → 4 Zn (NO₃)₂ + 5H₂O + N₂O
Zn + 4HNO₃(conc.) → Zn (NO₃)₂ + 2H₂O + 2NO₂
Some metals (e.g., Cr, Al) do not dissolve in concentrated nitric acid because of the formation of a passive film of oxide on the surface.
Concentrated nitric acid also oxidises non–metals and their compounds. Iodine is oxidised to iodic acid, carbon to carbon dioxide, sulphur to H₂SO₄, and phosphorus to phosphoric acid.

I₂ + 10HNO₃ → 2HIO₃ + 10NO₂ + 4H₂O
C + 4HNO₃ → CO₂ + 2H₂O + 4NO₂
S₈ + 48HNO₃ → 8H₂SO₄ + 48NO₂ + 16H₂O
P₄ + 20HNO₃ → 4H₃PO₄ + 20NO₂ + 4H₂O

Brown Ring Test: The familiar brown ring test for nitrates depends on the ability of Fe²⁺ to reduce nitrates to nitric oxide, which reacts with Fe²⁺ to form a brown coloured complex. The test is usually carried out by adding dilute ferrous sulphate solution to an aqueous solution containing nitrate ion, and then carefully adding concentrated sulphuric acid along the sides of the test tube. A brown ring at the interface between the solution and sulphuric acid layers indicates the presence of nitrate ion in solution.

NO₃^– + 3Fe²⁺ + 4H⁺ → NO + 3Fe³⁺ + 2H₂O
[Fe (H₂O)₆ ]²⁺ + NO → [Fe (H₂O)₅ (NO)]
²⁺+ H₂O
(brown)

Uses: The major use of nitric acid is in the manufacture of ammonium nitrate for fertilisers and other nitrates for use in explosives and pyrotechnics. It is also used for the preparation of nitroglycerin, trinitrotoluene and other organic nitro compounds. Other major uses are in the pickling of stainless steel, etching of metals and as an oxidiser in rocket fuels.

7.6 Phosphorus — Alltropic Forms

Phosphorus is found in many allotropic forms, the important ones being white, red and black. White phosphorus is a translucent white waxy solid. It is poisonous, insoluble in water but soluble in carbon disulphide and glows in dark (chemiluminescence). It dissolves in boiling NaOH solution in an inert atmosphere giving PH₃.
P₄ + 3NaOH + 3H₂O → PH₃ + 3NaH₂PO₂
( sodium hypophosphite )

White phosphorus is less stable and therefore, more reactive than the other solid phases under normal conditions because of angular strain in the P4 molecule where the angles are only 60°. It readily catches fire in air to give dense white fumes of P₄O₁₀.
P₄ + 5O₂ → P₄O₁₀

It consists of discrete tetrahedral P₄ molecule as shown in Fig. 7.2.

Red phosphorus is obtained by heating white phosphorus at 573K in an inert atmosphere for several days. When red phosphorus is heated under high pressure, a series of phases of black phosphorus is formed. Red phosphorus possesses iron grey lustre. It is odourless, non- poisonous and insoluble in water as well as in carbon disulphide. Chemically, red phosphorus is much less reactive than white phosphorus. It does not glow in the dark.

It is polymeric, consisting of chains of P₄ tetrahedra linked together in the manner as shown in Fig. 7.3.

Black phosphorus has two forms α-black phosphorus and β-black phosphorus. α-Black phosphorus is formed when red phosphorus is heated in a sealed tube at 803K. It can be sublimed Fig.7.3: Red phosphorus in air and has opaque monoclinic or rhombohedral crystals. It does not oxidise in air. β-Black phosphorus is prepared by heating white phosphorus at 473 K under high pressure. It does not burn in air upto 673 K.

7.7 Phosphine

Preparation
Phosphine is prepared by the reaction of calcium phosphide with water or dilute HCl.
Ca₃P₂ + 6H₂O → 3Ca(OH)₂ + 2PH₃
Ca₃P₂ + 6HCl → 3CaCl₂ + 2PH₃
In the laboratory, it is prepared by heating white phosphorus with concentrated NaOH solution in an inert atmosphere of CO₂.
P₄ + 3NaOH + 3H₂O → PH₃ + 3NaH₂ PO₂
(sodium hypophosphite)
When pure, it is non inflammable but becomes inflammable owing to the presence of P₂H₄ or P₄ vapours. To purify it from the impurities, it is absorbed in HI to form phosphonium iodide (PH₄I) which on treating with KOH gives off phosphine.
PH₄I + KOH → KI + H₂O + PH₃

Properties

It is a colourless gas with rotten fish smell and is highly poisonous. It explodes in contact with traces of oxidising agents like HNO₃, Cl₂ and Br₂ vapours.

It is slightly soluble in water. The solution of PH₃ in water decomposes in presence of light giving red phosphorus and H₂. When absorbed in copper sulphate or mercuric chloride solution, the corresponding phosphides are obtained.
3CuSO₄ + 2PH₃ → Cu₃ P₂ + 3H₂SO₄
3HgCl₂ + 2PH₃ → Hg₃P₂ + 6HCl

Phosphine is weakly basic and like ammonia, gives phosphonium compounds with acids e.g.,
PH₃ + HBr → PH₄ Br

Uses: The spontaneous combustion of phosphine is technically used in Holme’s signals. Containers containing calcium carbide and calcium phosphide are pierced and thrown in the sea when the gases evolved burn and serve as a signal. It is also used in smoke screens.

Example 7.6
In what way can it be proved that PH3 is basic in nature?
Solution
PH₃ reacts with acids like HI to form PH₄I which shows that it is basic in nature.
PH₃ + HI → PH₄I
Due to lone pair on phosphorus atom, PH₃ is acting as a Lewis base in the above reaction.

Intext Questions
7.7 Bond angle in PH₄⁺ is higher than that in PH₃. Why?
7.8 What happens when white phosphorus is heated with concentrated NaOH solution in an inert atmosphere of CO₂ ?

7.8 Phosphorus Halides

Phosphorus forms two types of halides, PX₃ (X = F, Cl, Br, I) and PX5 (X = F, Cl, Br).

7.8.1 Phosphorus Trichloride

Preparation

It is obtained by passing dry chlorine over heated white phosphorus.
P₄ + 6Cl₂ → 4PCl₃

It is also obtained by the action of thionyl chloride with white phosphorus.
P₄ + 8SOCl₂ → 4PCl₃ + 4SO₂ + 2S₂Cl₂

Properties

It is a colourless oily liquid and hydrolyses in the presence of moisture.
PCl₃ + 3H₂O →H₃PO₃ + 3HCl

It reacts with organic compounds containing –OH group such as CH₃COOH, C₂H₅OH.
3CH₃COOH + PCl₃ → 3CH₃COCl + H₃PO₃
3C₂H₅OH + PCl₃ → 3C₂H₅Cl + H₃PO₃

It has a pyramidal shape as shown, in which phosphorus is sp³ hybridised.

7.8.2 Phosphorus Pentachloride

Preparation

Phosphorus pentachloride is prepared by the reaction of white phosphorus with excess of dry chlorine.
P₄ + 10Cl₂ → 4PCl₅

It can also be prepared by the action of SO2Cl2 on phosphorus.
P₄ + 10SO₂Cl₂ → 4PCl₅ + 10SO₂

Properties

PCl₅ is a yellowish white powder and in moist air, it hydrolyses to POCl₃ and finally gets converted to phosphoric acid.
PCl₅ + H₂O → POCl₃ + 2HCl
POCl₃ + 3H₂O → H₃PO₄ + 3HCl

When heated, it sublimes but decomposes on stronger heating.

It reacts with organic compounds containing –OH group converting them to chloro derivatives.
C₂H₅OH + PCl₅ → C₂H₅Cl + POCl₃ + HCl
CH₃COOH + PCl₅ → CH₃COCl + POCl₃ +HCl

Finely divided metals on heating with PCl₅ give corresponding chlorides.
2Ag + PCl₅ → 2AgCl + PCl₃
Sn + 2PCl₅ → SnCl₄ + 2PCl₃

It is used in the synthesis of some organic compounds, e.g., C₂H₅Cl, CH₃COCl.

In gaseous and liquid phases, it has a trigonal bipyramidal structure as shown. The three equatorial P–Cl bonds are equivalent, while the two axial bonds are longer than equatorial bonds. This is due to the fact that the axial bond pairs suffer more repulsion as compared to equatorial bond pairs.

In the solid state it exists as an ionic solid, [PCl₄] [PCl₆] in which the cation, [PCl₄] is tetrahedral and the anion, [PCl₆] octahedral.

Example 7.7 Why does PCl₃ fume in moisture ?
Solution
PCl₃ hydrolyses in the presence of moisture giving fumes of HCl.
PCl₃ + 3H₂O →H₃PO₃ + 3HCl

Example 7.8 Are all the five bonds in PCl₅ molecule equivalent? Justify your answer.
Solution
PCl₅ has a trigonal bipyramidal structure and the three equatorial P-Cl bonds are equivalent, while the two axial bonds are different and longer than equatorial bonds.

Intext Questions
7.9 What happens when PCl₅ is heated?
7.10 Write a balanced equation for the hydrolytic reaction of PCl₅ in heavy water.

7.9 Oxoacids of Phosphorus

Phosphorus forms a number of oxoacids. The important oxoacids of phosphorus with their formulas, methods of preparation and the presence of some characteristic bonds in their structures are given in Table 7.5.

Table 7.5: Oxoacids of Phosphorus
Name	Formula	Oxidation state of phosphorus	Characteristics bonds and their number	Preparation
Hypophosphorus(phosphinic)	H₃PO₂	+1	One P – OH Two P – OH One P = O	white P₄ + alkali
Orthophosphorous(phosphonic)	H₃PO₃	+3	Two P – OH One P – OH One P = O	P₂O₃
Pyrophosphorous	H₄P₂O₅	+3	Two P – OH two P – OH Two P = O	PCl₃ + H₃PO₃
Hypophosphoric	H₄P₂O₆	+4	Four P – OH two P – OH One P = O	red P₄ + alkali
Orthophosphoric	H₃PO₄	+5	Three P – OH One P – OH	P₄O₁₀+H₂O
Pyrophosphoric	H₄P₂O₇	+5	Two P – OH Two P – OH One P-O-P	heat phosphoric acid
Metaphosphoric	(HPO₃)_n	+5	Three P – OH Three P – OH Three P-O-P	phosphorus acid + Br₂, heat in a sealed tube

The compositions of the oxoacids are interrelated in terms of loss or gain of H₂O molecule or O-atom. The structures of some important oxoacids are given below:

In oxoacids phosphorus is tetrahedrally surrounded by other atoms. All these acids contain at least one P=O bond and one P–OH bond. The oxoacids in which phosphorus has lower oxidation state (less than +5) contain, in addition to P=O and P–OH bonds, either P–P (e.g., in H₄P₂O₆) or P–H (e.g., in H₃PO₂) bonds but not both. These acids in +3 oxidation state of phosphorus tend to disproportionate to higher and lower oxidation states. For example, orthophophorous acid (or phosphorous acid) on heating disproportionates to give orthophosphoric acid (or phosphoric acid) and phosphine.
4H₃PO₃ → 3H₃PO₄ + PH₃

The acids which contain P–H bond have strong reducing properties. Thus, hypophosphorous acid is a good reducing agent as it contains two P–H bonds and reduces, for example, AgNO₃ to metallic silver.
4 AgNO₃ + 2H₂O + H₃PO₂ → 4Ag + 4HNO₃ + H₃PO₄

These P–H bonds are not ionisable to give H⁺ and do not play any role in basicity. Only those H atoms which are attached with oxygen in P–OH form are ionisable and cause the basicity. Thus, H₃PO₃ and H₃PO₄ are dibasic and tribasic, respectively as the structure of H₃PO₃ has two P–OH bonds and H₃PO₄ three.

Example 7.9
How do you account for the reducing behaviour of H₃PO₂ on the basis of its structure ?
Solution
In H₃PO₂, two H atoms are bonded directly to P atom which imparts reducing character to the acid.

Intext Questions
7.11 What is the basicity of H₃PO₄?
7.12 What happens when H₃PO₃ is heated?

7.10 Group 16 Elements

Oxygen, sulphur, selenium, tellurium and polonium constitute Group 16 of the periodic table. This is sometimes known as group of chalcogens. The name is derived from the Greek word for brass and points to the association of sulphur and its congeners with copper. Most copper minerals contain either oxygen or sulphur and frequently the other members of the group.

7.10.1 Occurrence

Oxygen is the most abundant of all the elements on earth. Oxygen forms about 46.6% by mass of earth’s crust. Dry air contains 20.946% oxygen by volume.
However, the abundance of sulphur in the earth’s crust is only 0.03-0.1%. Combined sulphur exists primarily as sulphates such as gypsum CaSO₄.2H₂O, epsom salt MgSO₄.7H₂O, baryte BaSO₄ and sulphides such as galena PbS, zinc blende ZnS, copper pyrites CuFeS₂. Traces of sulphur occur as hydrogen sulphide in volcanoes. Organic materials such as eggs, proteins, garlic, onion, mustard, hair and wool contain sulphur.
Selenium and tellurium are also found as metal selenides and tellurides in sulphide ores. Polonium occurs in nature as a decay product of thorium and uranium minerals.
The important atomic and physical properties of Group16 along with electronic configuration are given in Table 7.6. Some of the atomic, physical and chemical properties and their trends are discussed below.

7.10.2 Electronic Configuration

The elements of Group16 have six electrons in the outermost shell and have ns² np⁴ general electronic configuration.

7.10.3 Atomic and Ionic Radii

Due to increase in the number of shells, atomic and ionic radii increase from top to bottom in the group. The size of oxygen atom is, however, exceptionally small.

7.10.4 Ionisation Enthalpy

Ionisation enthalpy decreases down the group. It is due to increase in size. However, the elements of this group have lower ionisation enthalpy values compared to those of Group15 in the corresponding periods. This is due to the fact that Group 15 elements have extra stable half- filled p orbitals electronic configurations.

7.10.5 Electron Gain Enthalpy

Because of the compact nature of oxygen atom, it has less negative electron gain enthalpy than sulphur. However, from sulphur onwards the value again becomes less negative upto polonium.

7.10.6 Electronegativity

Next to fluorine, oxygen has the highest electronegativity value amongst the elements. Within the group, electronegativity decreases with an increase in atomic number. This implies that the metallic character increases from oxygen to polonium.

Example 7.10
Elements of Group 16 generally show lower value of first ionisation enthalpy compared to the corresponding periods of group 15. Why?
Solution
Due to extra stable half-filled p orbitals electronic configurations of Group 15 elements, larger amount of energy is required to remove electrons compared to Group 16 elements.

7.10.7 Physical Properties

Some of the physical properties of Group 16 elements are given in Table 7.6. Oxygen and sulphur are non-metals, selenium and tellurium metalloids, whereas polonium is a metal. Polonium is radioactive and is short lived (Half-life 13.8 days). All these elements exhibit allotropy. The melting and boiling points increase with an increase in atomic number down the group. The large difference between the melting and boiling points of oxygen and sulphur may be explained on the basis of their atomicity; oxygen exists as diatomic molecule (O₂) whereas sulphur exists as polyatomic molecule (S₈).

7.10.8 Chemical Properties

Oxidation states and trends in chemical reactivity The elements of Group 16 exhibit a number of oxidation states (Table 7.6). The stability of -2 oxidation state decreases down the group. Polonium hardly shows –2 oxidation state. Since electronegativity of oxygen is very high, it shows only negative oxidation state as –2 except in the case of OF₂ where its oxidation state is + 2. Other elements of the group exhibit + 2, + 4, + 6 oxidation states but + 4 and + 6 are more common. Sulphur, selenium and tellurium usually show + 4 oxidation state in their compounds with oxygen and + 6 with fluorine. The stability of + 6 oxidation state decreases down the group and stability of + 4 oxidation state increases (inert pair effect). Bonding in +4 and +6 oxidation states is primarily covalent.

Table 7.6: Some Physical Properties of Group 16 Elements
Peoperty	O	S	Se	Te	Po
Atomic number	8	16	34	52	84
Atomic mass/g mol^-1	16.00	32.06	78.96	127.60	210.00
Electronic configuration	[He]2s²2p⁴	[Ne]3s²3p⁴	[Ar]3d¹⁰4s²4p⁴	[Kr]4d¹⁰5s²5p⁴	[Ar]4f¹⁴5d¹⁰6s²6p⁴
Covalent radius/(pm)^a	66	104	117	137	146
Ionic radius, E^2-/pm	140	184	198	221	230^b
Electron gain enthalpy,/Δ_egH kJ mol^-1	-141	-200	-195	-190	-174
Ionisation enthalpy (Δ_iH_i)/kJ mol^-1	1314	1000	941	869	813
Electronegetivity	3.50	2.44	2.48	2.01	1.76
Density /g cm^-3(298 K)	1.32^c	2.06^d	4.19^e	6.25	–
Melting point/K	55	393^f	490	725	520
Boiling point/K	90	718	958	1260	1235
Oxidation states	-2,-1,1,2	-2,2,4,6	-2,2,4,6	-2,2,4,6	2,4

Anomalous behaviour of oxygen

The anomalous behaviour of oxygen, like other members of p-block present in second period is due to its small size and high electronegativity. One typical example of effects of small size and high electronegativity is the presence of strong hydrogen bonding in H₂O which is not found in H₂S.
The absence of d orbitals in oxygen limits its covalency to four and in practice, rarely exceeds two. On the other hand, in case of other elements of the group, the valence shells can be expanded and covalence exceeds four.

(i) Reactivity with hydrogen: All the elements of Group 16 form hydrides of the type H2E (E = O, S, Se, Te, Po). Some properties of hydrides are given in Table 7.7. Their acidic character increases from H₂O to H₂Te. The increase in acidic character can be explained in terms of decrease in bond (H–E) dissociation enthalpy down the group. Owing to the decrease in bond (H–E) dissociation enthalpy down the group, the thermal stability of hydrides also decreases from H₂O to H₂Po. All the hydrides except water possess reducing property and this character increases from H₂S to H₂Te.

b.p/K

Table 7.7: Properties of Hydrides of Group 16 Elements
Peoperty	H₂O	H₂S	H₂Se	H₂Te
m.p/K	273	188	208	222
373	213	232	269
H-E distance/pm	96	134	146	169
HEH angle()	104	92	91	90
Δ_fH/kJ mol^-1	-286	-20	73	100
Δ_dissH (H-E)/kJ mol^-1	463	347	276	238
Dissociation Constant^a	1.8×10^-16	1.3×10^-7	1.3×10^-4	2.3×10^-3

(ii) Reactivity with oxygen: All these elements form oxides of the EO₂ and EO₃ types where E = S, Se, Te or Po. Ozone (O₃) and sulphur dioxide (SO₂) are gases while selenium dioxide (SeO₂) is solid. Reducing property of dioxide decreases from SO₂ to TeO₂; SO₂ is reducing while TeO₂ is an oxidising agent. Besides EO₂ type, sulphur, selenium and tellurium also form EO₃ type oxides (SO₃, SeO₃, TeO₃). Both types of oxides are acidic in nature.

(iii) Reactivity towards the halogens: Elements of Group 16 form a large number of halides of the type, EX₆, EX₄ and EX₂ where E is an element of the group and X is a halogen. The stability of the halides decreases in the order F⁻ > Cl⁻ > Br⁻ > I⁻ . Amongst hexahalides, hexafluorides are the only stable halides. All hexafluorides are gaseous in nature. They have octahedral structure. Sulphur hexafluoride, SF₆ is exceptionally stable for steric reasons.

Amongst tetrafluorides, SF₄ is a gas, SeF₄ a liquid and TeF₄ a solid. These fluorides have sp³ d hybridisation and thus, have trigonal bipyramidal structures in which one of the equatorial positions is occupied by a lone pair of electrons. This geometry is also regarded as see-saw geometry.

All elements except selenium form dichlorides and dibromides. These dihalides are formed by sp³ hybridisation and thus, have tetrahedral structure. The well known monohalides are dimeric in nature. Examples are S₂F₂, S₂Cl₂, S₂Br₂, Se₂Cl₂ and Se₂Br₂. These dimeric halides undergo disproportionation as given below:
2Se₂Cl₂ → SeCl₄ + 3Se

Example 7.11
H₂S is less acidic than H₂Te. Why?
Solution
Due to the decrease in bond (E–H) dissociation enthalpy down the group, acidic character increases.

Intext Question
7.13 List the important sources of sulphur.
7.14 Write the order of thermal stability of the hydrides of Group 16 elements.
7.15 Why is H₂O a liquid and H₂S a gas ?

7.11 Dioxygen

Preparation

Dioxygen can be obtained in the laboratory by the following ways:
(i) By heating oxygen containing salts such as chlorates, nitrates and permanganates.

(ii) By the thermal decomposition of the oxides of metals low in the
electrochemical series and higher oxides of some metals.
2Ag₂O(s) → 4Ag(s) + O₂(g); 2Pb₃O4(s) → 6PbO(s) + O₂(g)
2HgO(s) → 2Hg(l) + O₂(g) ; 2PbO₂(s) → 2PbO(s) + O₂(g)

(iii) Hydrogen peroxide is readily decomposed into water and dioxygen by catalysts such as finely divided metals and manganese dioxide.
2H₂O₂(aq) → 2H₂O(l) + O₂(g)

On large scale it can be prepared from water or air. Electrolysis of water leads to the release of hydrogen at the cathode and oxygen at the anode. Industrially, dioxygen is obtained from air by first removing carbon dioxide and water vapour and then, the remaining gases are liquefied and fractionally distilled to give dinitrogen and dioxygen.

Properties

Dioxygen is a colourless and odourless gas. Its solubility in water is to the extent of 3.08 cm in 100 cm water at 293 K which is just sufficient for the vital support of marine and aquatic life. It liquefies at 90 K and freezes at 55 K. Oxygen atom has three stable isotopes: ¹⁶O,¹⁷O and ¹⁸O. Molecular oxygen, O₂ is unique in being paramagnetic inspite of having even number of electrons (see Class XI Chemistry Book, Unit 4).

Dioxygen directly reacts with nearly all metals and non-metals except some metals ( e.g., Au, Pt) and some noble gases. Its combination with other elements is often strongly exothermic which helps in sustaining the reaction. However, to initiate the reaction, some external heating is required as bond dissociation enthalpy of oxgyen-oxygen double bond is high (493.4 kJ mol^–1).

Some of the reactions of dioxygen with metals, non-metals and other compounds are given below:
2Ca + O₂ → 2CaO
4Al + 3O₂ → 2Al₂O₃
P₄ + 5O₂ → P₄O₁₀
C + O₂ → CO₂
2ZnS + 3O₂ → 2ZnO + 2SO₂
CH₄ + 2O₂ → CO₂ + 2H₂O

Some compounds are catalytically oxidised. For example,

Uses: In addition to its importance in normal respiration and combustion processes, oxygen is used in oxyacetylene welding, in the manufacture of many metals, particularly steel. Oxygen cylinders are widely used in hospitals, high altitude flying and in mountaineering. The combustion of fuels, e.g., hydrazines in liquid oxygen, provides tremendous thrust in rockets.

Intext Questions
7.16 Which of the following does not react with oxygen directly?
Zn, Ti, Pt, Fe
7.17 Complete the following reactions:
(i) C₂H₄ + O₂ →
(ii) 4Al + 3O₂ →

7.12 Simple Oxides

A binary compound of oxygen with another element is called oxide. As already stated, oxygen reacts with most of the elements of the periodic table to form oxides. In many cases one element forms two or more oxides. The oxides vary widely in their nature and properties.

Oxides can be simple (e.g., MgO, Al₂O₃ ) or mixed (Pb₃O₄, Fe₃O₄). Simple oxides can be classified on the basis of their acidic, basic or amphoteric character. An oxide that combines with water to give an acid is termed acidic oxide (e.g., SO₂, Cl₂O₇, CO₂, N₂O₅ ). For example, SO₂ combines with water to give H₂SO₃, an acid.
SO₂ + H₂O → H₂SO3

As a general rule, only non-metal oxides are acidic but oxides of some metals in high oxidation state also have acidic character (e.g., Mn₂O₇, CrO₃, V₂O₅). The oxides which give a base with water are known as basic oxides (e.g., Na₂O, CaO, BaO). For example, CaO combines with water to give Ca(OH)₂, a base.
CaO + H₂O → Ca(OH)₂

In general, metallic oxides are basic.

Some metallic oxides exhibit a dual behaviour. They show characteristics of both acidic as well as basic oxides. Such oxides are known as amphoteric oxides. They react with acids as well as alkalies. For example, Al₂O₃ reacts with acids as well as alkalies.
Al₂O₃ ( s ) + 6HCl ( aq ) + 9H₂O ( l ) → 2 [ Al(H₂O)₆ ]³⁺ ( aq ) + 6Cl⁻ ( aq )
Al₂O₃ ( s ) + 6NaOH ( aq ) + 3H₂O ( l ) → 2Na₃[Al(OH)₆](aq)

There are some oxides which are neither acidic nor basic. Such oxides are known as neutral oxides. Examples of neutral oxides are CO, NO and N₂O.

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7.13 Ozone

There are some oxides which are neither acidic nor basic. Such oxides are known as neutral oxides. Examples of neutral oxides are CO, NO and N₂O. Ozone is an allotropic form of oxygen. It is too reactive to remain for long in the atmosphere at sea level. At a height of about 20 kilometres, it is formed from atmospheric oxygen in the presence of sunlight. This ozone layer protects the earth’s surface from an excessive concentration of ultraviolet (UV) radiations.

Preparation

When a slow dry stream of oxygen is passed through a silent electrical discharge, conversion of oxygen to ozone (10%) occurs. The product is known as ozonised oxygen.
3O₂ → 2O₃ ΔH^V (298 K) = +142 kJ mol⁻¹

Since the formation of ozone from oxygen is an endothermic process, it is necessary to use a silent electrical discharge in its preparation to prevent its decomposition.

If concentrations of ozone greater than 10 per cent are required, a battery of ozonisers can be used, and pure ozone (b.p. 385 K) can be condensed in a vessel surrounded by liquid oxygen.

Properties

Pure ozone is a pale blue gas, dark blue liquid and violet-black solid. Ozone has a characteristic smell and in small concentrations it is harmless. However, if the concentration rises above about 100 parts per million, breathing becomes uncomfortable resulting in headache and nausea.

Ozone is thermodynamically unstable with respect to oxygen since its decomposition into oxygen results in the liberation of heat (ΔH is negative) and an increase in entropy (ΔS is positive). These two effects reinforce each other, resulting in large negative Gibbs energy change (ΔG) for its conversion into oxygen. It is not really surprising, therefore, high concentrations of ozone can be dangerously explosive.

Due to the ease with which it liberates atoms of nascent oxygen (O₃ → O₂ + O), it acts as a powerful oxidising agent. For example, it oxidises lead sulphide to lead sulphate and iodide ions to iodine.
PbS(s) + 4O₃(g) → PbSO₄(s) + 4O₂(g)
2I^–(aq) + H₂O(l) + O₃(g) → 2OH^–(aq) + I₂(s) + O₂(g)

When ozone reacts with an excess of potassium iodide solution buffered with a borate buffer (pH 9.2), iodine is liberated which can be titrated against a standard solution of sodium thiosulphate. This is a quantitative method for estimating O₃ gas.

Experiments have shown that nitrogen oxides (particularly nitric oxide) combine very rapidly with ozone and there is, thus, the possibility that nitrogen oxides emitted from the exhaust systems of supersonic jet aeroplanes might be slowly depleting the concentration of the ozone layer in the upper atmosphere.
NO ( g ) + O₃ ( g ) → NO₂ ( g ) + O₂ ( g )

Another threat to this ozone layer is probably posed by the use of freons which are used in aerosol sprays and as refrigerants.

The two oxygen-oxygen bond lengths in the ozone molecule are identical (128 pm) and the molecule is angular as expected with a bond angle of about 117° . It is a resonance hybrid of two main forms:

Uses: It is used as a germicide, disinfectant and for sterilising water. It is also used for bleaching oils, ivory, flour, starch, etc. It acts as an oxidising agent in the manufacture of potassium permanganate.

Intext Questions
7.18 Why does O₃ act as a powerful oxidising agent?
7.19 How is O₃ estimated quantitatively?

7.14 Sulphur – Alltropic Forms

Sulphur forms numerous allotropes of which the yellow rhombic (α-sulphur) and monoclinic (β -sulphur) forms are the most important. The stable form at room temperature is rhombic sulphur, which transforms to monoclinic sulphur when heated above 369 K.

Rhombic sulphur (α-sulphur)

This allotrope is yellow in colour, m.p. 385.8 K and specific gravity 2.06. Rhombic sulphur crystals are formed on evaporating the solution of roll sulphur in CS₂. It is insoluble in water but dissolves to some extent in benzene, alcohol and ether. It is readily soluble in CS₂.

Monoclinic sulphur (β-sulphur)

Its m.p. is 393 K and specific gravity 1.98. It is soluble in CS₂. This form of sulphur is prepared by melting rhombic sulphur in a dish and cooling, till crust is formed. Two holes are made in the crust and the remaining liquid poured out. On removing the crust, colourless needle shaped crystals of β-sulphur are formed. It is stable above 369 K and transforms into α-sulphur below it. Conversely, α-sulphur is stable below 369 K and transforms into β-sulphur above this. At 369 K both the forms are stable. This temperature is called transition temperature.

Both rhombic and monoclinic sulphur have S₈ molecules. These S8 molecules are packed to give different crystal structures. The S₈ ring in both the forms is puckered and has a crown shape. The molecular dimensions are given in Fig. 7.5(a).

Several other modifications of sulphur containing 6-20 sulphur atoms per ring have been synthesised in the last two decades. In cyclo-S₆, the ring adopts the chair form and the molecular dimensions are as shown in Fig. 7.5 (b). At elevated temperatures (~1000 K), S₂ is the dominant species and is paramagnetic like O₂.

Example 7.12
Which form of sulphur shows paramagnetic behaviour ?
Solution
In vapour state sulphur partly exists as S₂ molecule which has two unpaired electrons in the antibonding π* orbitals like O₂ and, hence, exhibits paramagnetism.

7.15 Sulphur Dioxide

Preparation

Sulphur dioxide is formed together with a little (6-8%) sulphur trioxide when sulphur is burnt in air or oxygen:
S(s) + O₂(g) → SO₂ (g)

In the laboratory it is readily generated by treating a sulphite with dilute sulphuric acid.
SO₃ (aq) + 2H (aq) → H₂O(l) + SO₂ (g)

Industrially, it is produced as a by-product of the roasting of sulphide ores.
4FeS₂ (s ) + 11O₂ ( g ) → 2Fe₂O3 ( s ) + 8SO₂ ( g )

The gas after drying is liquefied under pressure and stored in steel cylinders.

Properties

Sulphur dioxide is a colourless gas with pungent smell and is highly soluble in water. It liquefies at room temperature under a pressure of two atmospheres and boils at 263 K.

Sulphur dioxide, when passed through water, forms a solution of sulphurous acid.
SO₂(g) + H₂O(l) → H₂SO₃(aq)

It reacts readily with sodium hydroxide solution, forming sodium sulphite, which then reacts with more sulphur dioxide to form sodium hydrogen sulphite.

2NaOH + SO₂ → Na₂SO₃ + H₂O
Na₂SO₃ + H₂O + SO₂ → 2NaHSO₃

In its reaction with water and alkalies, the behaviour of sulphur dioxide is very similar to that of carbon dioxide.

Sulphur dioxide reacts with chlorine in the presence of charcoal (which acts as a catalyst) to give sulphuryl chloride, SO₂Cl₂. It is oxidised to sulphur trioxide by oxygen in the presence of vanadium(V) oxide catalyst.
SO₂(g) + Cl₂ (g) → SO₂Cl₂(l)

When moist, sulphur dioxide behaves as a reducing agent. For example, it converts iron(III) ions to iron(II) ions and decolourises acidified potassium permanganate(VII) solution; the latter reaction is a convenient test for the gas.
2Fe³⁺ + SO₂ + 2H₂O → 2Fe²⁺ + SO^{2 −}₄ + 4H⁺
5SO₂+ 2MnO₄ + 2H₂O → 5SO₄²⁻ + 4H⁺ + 2Mn²⁺
The molecule of SO₂ is angular. It is a resonance hybrid of the two canonical forms:

Uses: Sulphur dioxide is used (i) in refining petroleum and sugar (ii) in bleaching wool and silk and (iii) as an anti-chlor, disinfectant and preservative. Sulphuric acid, sodium hydrogen sulphite and calcium hydrogen sulphite (industrial chemicals) are manufactured from sulphur dioxide. Liquid SO₂ is used as a solvent to dissolve a number of organic and inorganic chemicals.

Intext Questions
7.20 What happens when sulphur dioxide is passed through an aqueous solution of Fe(III) salt?
7.21 Comment on the nature of two S–O bonds formed in SO₂ molecule. Are the two S–O bonds in this molecule equal ?
7.22 How is the presence of SO₂ detected ?

7.16 Oxoacid of Sulphur

Sulphur forms a number of oxoacids such as H₂SO₃, H₂S₂O₃, H₂S₂O₄, H₂S₂O₅, H₂SxO₆ (x = 2 to 5), H₂SO₄, H₂S₂O₇, H₂SO₅, H₂S₂O₈ . Some of these acids are unstable and cannot be isolated. They are known in aqueous solution or in the form of their salts. Structures of some important oxoacids are shown in Fig. 7.6.

7.17 Sulphuric Acid
Manufacture
Sulphuric acid is one of the most important industrial chemicals worldwide.
Sulphuric acid is manufactured by the Contact Process which involves three steps:
(i) burning of sulphur or sulphide ores in air to generate SO₂.
(ii) conversion of SO₂ to SO₃ by the reaction with oxygen in the presence of a catalyst (V₂O₅), and
(iii) absorption of SO₃ in H₂SO₄ to give Oleum (H₂S₂O₇).
A flow diagram for the manufacture of sulphuric acid is shown in (Fig. 7.7). The SO₂ produced is purified by removing dust and other impurities such as arsenic compounds.
The key step in the manufacture of H₂SO₄ is the catalytic oxidation of SO₂ with O₂ to give SO₃ in the presence of V₂O₅ (catalyst).

The reaction is exothermic, reversible and the forward reaction leads to a decrease in volume. Therefore, low temperature and high pressure are the favourable conditions for maximum yield. But the temperature should not be very low otherwise rate of reaction will become slow.

In practice, the plant is operated at a pressure of 2 bar and a temperature of 720 K. The SO₃ gas from the catalytic converter is absorbed in concentrated H₂SO₄ to produce oleum. Dilution of oleum with water gives H₂SO₄ of the desired concentration. In the industry two steps are carried out simultaneously to make the process a continuous one and also to reduce the cost.
SO₃ + H₂SO₄ → H₂S₂O₇
(Oleum)
The sulphuric acid obtained by Contact process is 96-98% pure.

Properties
Sulphuric acid is a colourless, dense, oily liquid with a specific gravity of 1.84 at 298 K. The acid freezes at 283 K and boils at 611 K. It dissolves in water with the evolution of a large quantity of heat. Hence, care must be taken while preparin g sulphuric acid solution from concentrated sulphuric acid. The concentrated acid must be added slowly into water with constant stirring.

The chemical reactions of sulphuric acid are as a result of the following characteristics: (a) low volatility (b) strong acidic character (c) strong affinity for water and (d) ability to act as an oxidising agent. In aqueous solution, sulphuric acid ionises in two steps.

H₂SO₄(aq) + H₂O(l) → H₃O⁺ (aq) + HSO₄⁻ (aq); K_a₁ = very large ( K_a₁ >10)
HSO₄ (aq) + H₂O(l) → H₃O⁺ (aq) + SO₄²⁻ (aq) ; K_a₂ > = 1.2 × 10⁻²

The larger value of K_a₁ ( K_a₁ >10) means that H₂SO₄ is largely dissociated into H⁺ and HSO₄ . Greater the value of dissociation constant (K_a), the stronger is the acid.

The acid forms two series of salts: normal sulphates (such as sodium sulphate and copper sulphate) and acid sulphates (e.g., sodium hydrogen sulphate).

Sulphuric acid, because of its low volatility can be used to manufacture more volatile acids from their corresponding salts.

2 MX + H₂SO₄ → 2HX + M₂SO₄ (X = F, Cl, NO₃)
(M = Metal)

Concentrated sulphuric acid is a strong dehydrating agent. Many wet gases can be dried by passing them through sulphuric acid, provided the gases do not react with the acid. Sulphuric acid removes water from organic compounds; it is evident by its charring action on carbohydrates.

Hot concentrated sulphuric acid is a moderately strong oxidising agent. In this respect, it is intermediate between phosphoric and nitric acids. Both metals and non-metals are oxidised by concentrated sulphuric acid, which is reduced to SO₂.
Cu + 2 H₂SO₄(conc.) → CuSO₄ + SO₂ + 2H₂O
3S + 2H₂SO₄(conc.) → 3SO₂ + 2H₂O
C + 2H₂SO₄(conc.) → CO₂ + 2 SO₂ + 2 H₂O

Uses: Sulphuric acid is a very important industrial chemical. A nation’s industrial strength can be judged by the quantity of sulphuric acid it produces and consumes. It is needed for the manufacture of hundreds of other compounds and also in many industrial processes. The bulk of sulphuric acid produced is used in the manufacture of fertilisers (e.g., ammonium sulphate, superphosphate). Other uses are in: (a) petroleum refining (b) manufacture of pigments, paints and dyestuff intermediates (c) detergent industry (d) metallurgical applications (e.g., cleansing metals before enameling, electroplating and galvanising (e) storage batteries (f) in the manufacture of nitrocellulose products and (g) as a laboratory reagent.

Example 7.13
What happens when
(i) Concentrated H₂SO₄ is added to calcium fluoride
(ii) SO₃ is passed through water?
Solution
(i) It forms hydrogen fluoride
CaF₂ + H₂SO₄ → CaSO₄ + 2HF
(ii) It dissolves SO₃ to give H₂SO₄ . SO₃ + H₂O → H₂SO₄

Intext Questions
7.23 Mention three areas in which H₂SO₄ plays an important role.
7.24 Write the conditions to maximise the yield of H₂SO₄ by Contact process.
7.25 Why is K_a₂ << K_a₁ for H₂SO₄ in water ?

7.18 Group 17 Elements

Fluorine, chlorine, bromine, iodine and astatine are members of Group 17. These are collectively known as the halogens (Greek halo means salt and genes means born i.e., salt producers). The halogens are highly reactive non-metallic elements. Like Groups 1 and 2, the elements of Group 17 show great similarity amongst themselves. That much similarity is not found in the elements of other groups of the periodic table. Also, there is a regular gradation in their physical and chemical properties. Astatine is a radioactive element.

7.18.1 Occurrence

Fluorine and chlorine are fairly abundant while bromine and iodine less so. Fluorine is present mainly as insoluble fluorides (fluorspar CaF₂, cryolite Na₃AlF₆ and fluoroapatite 3Ca₃(PO₄)₂.CaF₂) and small quantities are present in soil, river water plants and bones and teeth of animals. Sea water contains chlorides, bromides and iodides of sodium, potassium, magnesium and calcium, but is mainly sodium chloride solution (2.5% by mass). The deposits of dried up seas contain these compounds, e.g., sodium chloride and carnallite, KCl.MgCl₂.6H₂O. Certain forms of marine life contain iodine in their systems; various seaweeds, for example, contain upto 0.5% of iodine and Chile saltpetre contains upto 0.2% of sodium iodate.

The important atomic and physical properties of Group 17 elements along with their electronic configurations are given in Table 7.8.

Table 7.8: Atomic and physical Properties of Halogens
Peoperty	F	Cl	Br	I	At^a
^aRadioactive;^bPauling scale;^cFor the liquid at temperatures (K) given in the parentheses;^d solid; ^e The half-cell reaction is X₂(g) + 2e^– → 2X (aq).
Atomic number	9	17	35	53	85
Atomic mass/g mol^-1	19.00	35.42	79.90	126.90	210
Electronic configuration	[He]2s²2p⁵	[Ne]3s²3p⁵	[Ar]3d¹⁰4s²4p⁵	[Kr]4d¹⁰5s²5p⁵	[Ar]4f¹⁴5d¹⁰6s²6p⁵
Covalent radius/(pm)^a	64	99	114	133	–
Ionic radius, X^–/pm	133	184	196	220	–
Ionisation enthalpy (Δ_iH_i)/kJ mol^-1	1680	1256	1142	1008	–
Electron gain enthalpy/kJ mol^-1	-333	-349	-325	-296	–
Electronegetivity	4	3.2	3.0	2.7	2.2
Δ_HydH(X^–)/kJ mol^-1	515	381	347	305	–
	F₂	Cl₂	Br₂	I₂	–
Melting point/K	54.4	172.0	265.8	386.6	–
Boiling point/K	84.9	239.0	332.5	458.2	–
Density/g cm^-3	1.5 (85)^c	1.66(203)^c	3.19(273)^c	4.49(293)d	–
Distance X- X/pm^-3	143	199	228	266	–
Bond dissociation enthalpy/(kJ mol^-1	158.8	242.2	192.8	151.1	–
E^V/V^e	2.87	1.36	1.09	0.54	–

The trends of some of the atomic, physical and chemical properties are discussed below.

7.18.2 Electronic Configuration

All these elements have seven electrons in their outermost shell (ns² np⁵ ) which is one electron short of the next noble gas.

7.18.3 Atomic and Ionic Radii

The halogens have the smallest atomic radii in their respective periods due to maximum effective nuclear charge. The atomic radius of fluorine like the other elements of second period is extremely small. Atomic and ionic radii increase from fluorine to iodine due to increasing number of quantum shells.

7.18.4 Ionisation Enthalpy

They have little tendency to lose electron. Thus they have very high ionisation enthalpy. Due to increase in atomic size, ionisation enthalpy decreases down the group.

7.18.5 Electron Gain Enthalpy

Halogens have maximum negative electron gain enthalpy in the corresponding periods. This is due to the fact that the atoms of these elements have only one electron less than stable noble gas configurations. Electron gain enthalpy of the elements of the group becomes less negative down the group. However, the negative electron gain enthalpy of fluorine is less than that of chlorine. It is due to small size of fluorine atom. As a result, there are strong interelectronic repulsions in the relatively small 2p orbitals of fluorine and thus, the incoming electron does not experience much attraction.

7.18.6 Electronegativity

They have very high electronegativity. The electronegativity decreases down the group. Fluorine is the most electronegative element in the periodic table.

Example 7.14
Halogens have maximum negative electron gain enthalpy in the respective periods of the periodic table. Why?
Solution
Halogens have the smallest size in their respective periods and therefore high effective nuclear charge. As a consequence, they readily accept one electron to acquire noble gas electronic configuration.

7.18.7 Physical Properties

Halogens display smooth variations in their physical properties. Fluorine and chlorine are gases, bromine is a liquid and iodine is a solid. Their melting and boiling points steadily increase with atomic number. All halogens are coloured. This is due to absorption of radiations in visible region which results in the excitation of outer electrons to higher energy level. By absorbing different quanta of radiation, they display different colours. For example, F₂, has yellow, Cl₂ , greenish yellow, Br₂, red and I₂, violet colour. Fluorine and chlorine react with water. Bromine and iodine are only sparingly soluble in water but are soluble in various organic solvents such as chloroform, carbon tetrachloride, carbon disulphide and hydrocarbons to give coloured solutions.
One curious anomaly we notice from Table 7.8 is the smaller enthalpy of dissociation of F₂ compared to that of Cl₂ whereas X-X bond dissociation enthalpies from chlorine onwards show the expected trend: Cl – Cl > Br – Br > I – I. A reason for this anomaly is the relatively large electron-electron repulsion among the lone pairs in F₂ molecule where they are much closer to each other than in case of Cl₂.

Example 7.15
Although electron gain enthalpy of fluorine is less negative as compared to chlorine, fluorine is a stronger oxidising agent than chlorine. Why?
Solution
It is due to
(i) low enthalpy of dissociation of F-F bond (Table 7.8).
(ii) high hydration enthalpy of F⁻ (Table 7.8).

7.18.8 Chemical Properties

Oxidation states and trends in chemical reactivity

All the halogens exhibit –1 oxidation state. However, chlorine, bromine and iodine exhibit + 1, + 3, + 5 and + 7 oxidation states also as explained below:

The higher oxidation states of chlorine, bromine and iodine are realised mainly when the halogens are in combination with the small and highly electronegative fluorine and oxygen atoms. e.g., in interhalogens, oxides and oxoacids. The oxidation states of +4 and +6 occur in the oxides and oxoacids of chlorine and bromine. The fluorine atom has no d orbitals in its valence shell and therefore cannot expand its octet. Being the most electronegative, it exhibits only –1 oxidation state.

All the halogens are highly reactive. They react with metals and non-metals to form halides. The reactivity of the halogens decreases down the group.

The ready acceptance of an electron is the reason for the strong oxidising nature of halogens. F₂ is the strongest oxidising halogen and it oxidises other halide ions in solution or even in the solid phase. In general, a halogen oxidises halide ions of higher atomic number.
F₂ + 2X^– → 2F^– + X₂ (X = Cl, Br or I)
Cl₂ + 2X^– → 2Cl^– + X₂ (X = Br or I)
Br₂ + 2I^– → 2Br^– + I₂
The decreasing oxidising ability of the halogens in aqueous solution down the group is evident from their standard electrode potentials (Table 7.8) which are dependent on the parameters indicated below:

The relative oxidising power of halogens can further be illustrated by their reactions with water. Fluorine oxidises water to oxygen whereas chlorine and bromine react with water to form corresponding hydrohalic and hypohalous acids. The reaction of iodine with water is non- spontaneous. In fact, I⁻ can be oxidised by oxygen in acidic medium; just the reverse of the reaction observed with fluorine
2F₂ (g) + 2H₂O (l) → 4H⁺ (aq) + 4F⁻ (aq) + O₂ (g)
X₂ (g) + H₂O (l) → HX (aq) + HOX (aq)
( where X = Cl or Br )
4I⁻ (aq) + 4H⁺ (aq) + O₂ (g) → 2I₂ (s) + 2H₂O (l)

Anomalous behaviour of fluorine

Like other elements of p-block present in second period of the periodic table, fluorine is anomalous in many properties. For example, ionisation enthalpy, electronegativity, and electrode potentials are all higher for fluorine than expected from the trends set by other halogens. Also, ionic and covalent radii, m.p. and b.p., enthalpy of bond dissociation and electron gain enthalpy are quite lower than expected. The anomalous behaviour of fluorine is due to its small size, highest electronegativity, low F-F bond dissociation enthalpy, and non availability of d orbitals in valence shell.
Most of the reactions of fluorine are exothermic (due to the small and strong bond formed by it with other elements). It forms only one oxoacid while other halogens form a number of oxoacids. Hydrogen fluoride is a liquid (b.p. 293 K) due to strong hydrogen bonding. Other hydrogen halides are gases.

(i) Reactivity towards hydrogen: They all react with hydrogen to give hydrogen halides but affinity for hydrogen decreases from fluorine to iodine. Hydrogen halides dissolve in water to form hydrohalic acids. Some of the properties of hydrogen halides are given in Table 7.9. The acidic strength of these acids varies in the order: HF < HCl < HBr < HI. The stability of these halides decreases down the group due to decrease in bond (H–X) dissociation enthalpy in the order: H–F > H–Cl > H–Br > H–I.

Table 7.9: Properties of Hydrogen Halides
Peoperty	HF	HCl	HBr	HI
Melting point/K	190	159	185	222
Boiling point/K	293	189	206	238
Bond length (H-X)/pm	91.7	127.4	141.4	160.9
Δ_dissH^v/kJ mol^-1	574	432	363	295
pK_a	3.2	-7.0	-9.5	-10.1

(ii) Reactivity towards oxygen: Halogens form many oxides with oxygen but most of them are unstable. Fluorine forms two oxides OF₂ and O₂F₂. However, only OF₂ is thermally stable at 298 K. These oxides are essentially oxygen fluorides because of the higher electronegativity of fluorine than oxygen. Both are strong fluorinating agents. O₂F₂ oxidises plutonium to PuF₆ and the reaction is used in removing plutonium as PuF₆ from spent nuclear fuel.

Chlorine, bromine and iodine form oxides in which the oxidation states of these halogens range from +1 to +7. A combination of kinetic and thermodynamic factors lead to the generally decreasing order of stability of oxides formed by halogens, I > Cl > Br. The higher oxides of halogens tend to be more stable than the lower ones.

Chlorine oxides, Cl₂O, ClO₂, Cl₂O₆ and Cl₂O₇ are highly reactive oxidising agents and tend to explode. ClO₂ is used as a bleaching agent for paper pulp and textiles and in water treatment.

The bromine oxides, Br₂O, BrO₂ , BrO₃ are the least stable halogen oxides (middle row anomally) and exist only at low temperatures. They are very powerful oxidising agents.

The iodine oxides, I₂O₄ , I₂O₅, I₂O₇ are insoluble solids and decompose on heating. I₂O₅ is a very good oxidising agent and is used in the estimation of carbon monoxide.

(iii) Reactivity towards metals: Halogens react with metals to form metal halides. For example, bromine reacts with magnesium to give magnesium bromide.
Mg ( s ) + Br₂ ( l ) → MgBr₂ ( s )

The ionic character of the halides decreases in the order MF > MCl > MBr > MI where M is a monovalent metal. If a metal exhibits more than one oxidation state, the halides in higher oxidation state will be more covalent than the one in lower oxidation state. For example, SnCl₄, PbCl₄, SbCl₅ and UF₆ are more covalent than SnCl₂, PbCl₂, SbCl₃ and UF₄ respectively.

(iv) Reactivity of halogens towards other halogens: Halogens combine amongst themselves to form a number of compounds known as interhalogens of the types XX ′ , XX₃′, XX₅′ and XX₇′ where X is a larger size halogen and X’ is smaller size halogen.

Example 7.16
Fluorine exhibits only –1 oxidation state whereas other halogens exhibit + 1, + 3, + 5 and + 7 oxidation states also. Explain.
Solution
Fluorine is the most electronegative element and cannot exhibit any positive oxidation state. Other halogens have d orbitals and therefore, can expand their octets and show + 1, + 3, + 5 and + 7 oxidation states also.

Intext Questions
7.26 Considering the parameters such as bond dissociation enthalpy, electron gain enthalpy and hydration enthalpy, compare the oxidising power of F₂ and Cl₂.
7.27 Give two examples to show the anomalous behaviour of fluorine.
7.28 Sea is the greatest source of some halogens. Comment.

7.19 Chlorine

Chlorine was discovered in 1774 by Scheele by the action of HCl on MnO₂. In 1810 Davy established its elementary nature and suggested the name chlorine on account of its colour (Greek, chloros = greenish yellow).

Preparation

It can be prepared by any one of the following methods:
(i) By heating manganese dioxide with concentrated hydrochloric acid.
MnO₂ + 4HCl → MnCl₂ + Cl₂ + 2H₂O
However, a mixture of common salt and concentrated H₂SO₄ is used in place of HCl.
4NaCl + MnO₂ + 4H₂SO₄ → MnCl₂ + 4NaHSO₄ + 2H₂O + Cl₂
(ii) By the action of HCl on potassium permanganate.
2KMnO₄ + 16HCl → 2KCl + 2MnCl₂ + 8H₂O + 5Cl₂

Manufacture of chlorine
(i) Deacon’s process: By oxidation of hydrogen chloride gas by atmospheric oxygen in the presence of CuCl₂ (catalyst) at 723 K.

(ii) Electrolytic process: Chlorine is obtained by the electrolysis of brine (concentrated NaCl solution). Chlorine is liberated at anode. It is also obtained as a by–product in many chemical industries.

Properties

It is a greenish yellow gas with pungent and suffocating odour. It is about 2-5 times heavier than air. It can be liquefied easily into greenish yellow liquid which boils at 239 K. It is soluble in water.
Chlorine reacts with a number of metals and non-metals to form chlorides.
2Al + 3Cl₂ → 2AlCl₃ ; P₄ + 6Cl₂ → 4PCl₃
2Na + Cl₂ → 2NaCl; S₈ + 4Cl₂ → 4S₂Cl₂
2Fe + 3Cl₂ → 2FeCl₃ ;
It has great affinity for hydrogen. It reacts with compounds containing hydrogen to form HCl.
H₂ + Cl₂ → 2HCl
H₂S + Cl₂ → 2HCl + S
C₁₀H₁₆ + 8Cl₂ → 16HCl + 10C
With excess ammonia, chlorine gives nitrogen and ammonium chloride whereas with excess chlorine, nitrogen trichloride (explosive) is formed.

8NH₃ + 3Cl₂ → 6NH₄Cl + N₂;
NH₃ + 3Cl₂ → NCl₃ + 3HCl
(excess) (excess)
With cold and dilute alkalies chlorine produces a mixture of chloride and hypochlorite but with hot and concentrated alkalies it gives chloride and chlorate.
2NaOH + Cl₂ → NaCl + NaOCl + H₂O
(cold and dilute)
6 NaOH + 3Cl₂ → 5NaCl + NaClO₃ + 3H₂O
(hot and conc.)
With dry slaked lime it gives bleaching powder.
2Ca(OH)₂ + 2Cl₂ → Ca(OCl)₂ + CaCl₂ + 2H₂O

The composition of bleaching powder is Ca(OCl)₂.CaCl₂.Ca(OH)₂.2H₂O.
Chlorine reacts with hydrocarbons and gives substitution products with saturated hydrocarbons and addition products with unsaturated hydrocarbons. For example,

Chlorine water on standing loses its yellow colour due to the formation of HCl and HOCl. Hypochlorous acid (HOCl) so formed, gives nascent oxygen which is responsible for oxidising and bleaching properties of chlorine.
(i) It oxidises ferrous to ferric, sulphite to sulphate, sulphur dioxide to sulphuric acid and iodine to iodic acid.
2FeSO₄ + H₂SO₄ + Cl₂ → Fe₂(SO₄)₃ + 2HCl
Na₂SO₃ + Cl₂ + H₂O → Na₂SO₄ + 2HCl
SO₂ + 2H₂O + Cl₂ → H₂SO₄ + 2HCl
I₂ + 6H₂O + 5Cl₂ → 2HIO₃ + 10HCl

(ii) It is a powerful bleaching agent; bleaching action is due to oxidation.
Cl₂ + H₂O → 2HCl + O
Coloured substance + O → Colourless substance
It bleaches vegetable or organic matter in the presence of moisture. Bleaching effect of chlorine is permanent.

Uses: It is used (i) for bleaching woodpulp (required for the manufacture of paper and rayon), bleaching cotton and textiles, (ii) in the extraction of gold and platinum (iii) in the manufacture of dyes, drugs and organic compounds such as CCl₄, CHCl₃, DDT, refrigerants, etc. (iv) in sterilising drinking water and (v) preparation of poisonous gases such as phosgene (COCl₂), tear gas (CCl₃NO₂), mustard gas (ClCH₂CH₂SCH₂CH₂Cl).

Example 7.17 Write the balanced chemical equation for the reaction of Cl₂ with hot and concentrated NaOH. Is this reaction a disproportionation reaction? Justify.
Solution
3Cl₂ + 6NaOH → 5NaCl + NaClO₃ + 3H₂O
Yes, chlorine from zero oxidation state is changed to –1 and +5 oxidation states.

Intext Questions
7.29 Give the reason for bleaching action of Cl₂.
7.30 Name two poisonous gases which can be prepared from chlorine gas.

7.20 Hydrogen Chloride

Glauber prepared this acid in 1648 by heating common salt with concentrated sulphuric acid. Davy in 1810 showed that it is a compound of hydrogen and chlorine.

Preparation
In laboratory, it is prepared by heating sodium chloride with concentrated sulphuric acid.

HCl gas can be dried by passing through concentrated sulphuric acid.

Properties

It is a colourless and pungent smelling gas. It is easily liquefied to a colourless liquid (b.p.189 K) and freezes to a white crystalline solid (f.p. 159 K). It is extremely soluble in water and ionises as below:
HCl(g) + H₂O (l) → H₃O + (aq) + Cl⁻ (aq) K_a = 10⁷

Its aqueous solution is called hydrochloric acid. High value of dissociation constant (K_a) indicates that it is a strong acid in water. It reacts with NH₃ and gives white fumes of NH₄Cl.
NH₃ + HCl → NH₄Cl

When three parts of concentrated HCl and one part of concentrated HNO₃ are mixed, aqua regia is formed which is used for dissolving noble metals, e.g., gold, platinum.
Au + 4H⁺ + NO₃⁻ + 4Cl⁻ → AuCl⁻₄ + NO + 2H₂O
3Pt + 16H⁺ + 4NO₃ + 18Cl⁻ → 3PtCl₆⁻ + 4NO + 8H₂O

Hydrochloric acid decomposes salts of weaker acids, e.g., carbonates, hydrogencarbonates, sulphites, etc.
Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂
NaHCO₃ + HCl → NaCl + H₂O + CO₂
Na₂SO₃ + 2HCl → 2NaCl + H₂O + SO₂

Uses: It is used (i) in the manufacture of chlorine, NH₄Cl and glucose (from corn starch), (ii) for extracting glue from bones and purifying bone black, (iii) in medicine and as a laboratory reagent.

Example 7.18
When HCl reacts with finely powdered iron, it forms ferrous chloride and not ferric chloride. Why?
Solution
Its reaction with iron produces H₂.
Fe + 2HCl → FeCl₂ + H₂
Liberation of hydrogen prevents the formation of ferric chloride.

7.21 Oxoacids of Halogens
Due to high electronegativity and small size, fluorine forms only one oxoacid, HOF known as fluoric (I) acid or hypofluorous acid. The other halogens form several oxoacids. Most of them cannot be isolated in pure state. They are stable only in aqueous solutions or in the form of their salts. The oxoacids of halogens are given in Table 7.10 and their structures are given in Fig. 7.8.

Table 7.10: Oxoacids of Halogens
Halic(I) acid (Hypohalous acid)	HOF(Hypofluorous acid)	HOCl(Hypochlorous acid)	HOBr(Hypobromous acid)	HOI(Hypoiodous acid)
Halic (III) acid(Halous acid)	–	HOCIO(chlorous acid)	–	–
Halic (V) acid(Halic acid)	–	HOCIO₂(chloric acid)	HOBrO₂(bromic acid)	HOIO₂(ionic acid)
Halic(VII) acid(Perhalic acid)	–	HOCIO₃(perchloric acid)	HOBrO₃(perbromic acid)	HOIO₃(periodic acid)

7.22 Interhalogen Compounds

When two different halogens react with each other, interhalogen compounds are formed. They can be assigned general compositions as XX’ , XX’₃ , XX’₅ and XX’₇ where X is halogen of larger size and X’ of smaller size and X’ is more electropositive than X . As the ratio between radii of X and X’ increases, the number of atoms per molecule also increases. Thus, iodine (VII) fluoride should have maximum number of atoms as the ratio of radii between I and F should be maximum. That is why its formula is IF₇ (having maximum number of atoms).

Preparation

The interhalogen compounds can be prepared by the direct combination or by the action of halogen on lower interhalogen compounds. The product formed depends upon some specific conditions, For e.g.,

Properties

Some properties of interhalogen compounds are given in Table 7.11.

Table 7.10: Oxoacids of Halogens
Type	Formula	Physical state and color	Structure
^aVery unstable; ^bThe pure solid is known at room temperature; ^cDimerises as Clâ€“bridged dimer (I₂Cl₆)
XX’₁	ClF BrF IF^a BrCl^b ICl IBr	colorless gas pale brown gas detected spectroscopically gas ruby red solid(α-form) brown red solid (β – form) Black solid	– – – – – –
XX’₃	ClF₃ BrF₃ IF₃ ICl^c₃	colorless gasyellow green liquidyellow powder orange solid	Bent T-shaped Bent T-shaped Bent T-shaped(?) Bent T-shaped(?)
XX’₅	IF₅ BrF₅ ClF₅	colorless gas but solid below 77 K colorless liquidsquare pyramidal square pyramidal square pyramidal
XX’₇	IF₇	colorless gas	pentagonal bipyramidal

These are all covalent molecules and are diamagnetic in nature. They are volatile solids or liquids at 298 K except ClF which is a gas. Their physical properties are intermediate between those of constituent halogens except that their m.p. and b.p. are a little higher than expected.

Their chemical reactions can be compared with the individual halogens. In general, interhalogen compounds are more reactive than halogens (except fluorine). This is because X–X′ bond in interhalogens is weaker than X–X bond in halogens except F–F bond. All these undergo hydrolysis giving halide ion derived from the smaller halogen and a hypohalite ( when XX′), halite ( when XX′₃), halate (when XX′₅) and perhalate (when XX′₇) anion derived from the larger halogen.
XX’ + H₂O → HX’ + HOX

Their molecular structures are very interesting which can be explained on the basis of VSEPR theory (Example 7.19). The XX₃ compounds have the bent ‘T’ shape, XX₅ compounds square pyramidal and IF₇ has pentagonal bipyramidal structures (Table 7.11).

Example 7.19 Deduce the molecular shape of BrF₃ on the basis of VSEPR theory.
Solution
The central atom Br has seven electrons in the valence shell. Three of these will form electron- pair bonds with three fluorine atoms leaving behind four electrons. Thus, there are three bond pairs and two lone pairs. According to VSEPR theory, these will occupy the corners of a trigonal bipyramid. The two lone pairs will occupy the equatorial positions to minimise lone pair-lone pair and the bond pair- lone pair repulsions which are greater than the bond pair-bond pair repulsions. In addition, the axial fluorine atoms will be bent towards the equatorial fluorine in order to minimise the lone-pair-lone pair repulsions. The shape would be that of a slightly bent ‘T’.

Uses: These compounds can be used as non aqueous solvents. Interhalogen compounds are very useful fluorinating agents. ClF₃ and BrF₃ are used for the production of UF₆ in the enrichment of ²³⁵U.
U(s) + 3ClF₃(l) → UF₆(g) + 3ClF(g)

Intext Question
7.31 Why is ICl more reactive than I₂?

7.23 Group 18 Elements
Group 18 consists of six elements: helium, neon, argon, krypton, xenon and radon. All these are gases and chemically unreactive. They form very few compounds. Because of this they are termed noble gases.

7.23.1 Occurrence

All the noble gases except radon occur in the atmosphere. Their atmospheric abundance in dry air is ~ 1% by volume of which argon is the major constituent. Helium and sometimes neon are found in minerals of radioactive origin e.g., pitchblende, monazite, cleveite. The main commercial source of helium is natural gas. Xenon and radon are the rarest elements of the group. Radon is obtained as a decay product of ²²⁶Ra.
²²⁶₈₈Ra →²²²₈₆Rn +⁴₂He

Example 7.20 Why are the elements of Group 18 known as noble gases ?
Solution
The elements present in Group 18 have their valence shell orbitals completely filled and, therefore, react with a few elements only under certain conditions. Therefore, they are now known as noble gases.

The important atomic and physical properties of the Group 18 elements along with their electronic configurations are given in Table 7.12. The trends in some of the atomic, physical and chemical properties of the group are discussed here.

7.23.2 Electronic Configuration

All noble gases have general electronic configuration ns²np⁶ except helium which has 1s² (Table 7.12). Many of the properties of noble gases including their inactive nature are ascribed to their closed shell structures.

Atomic mass/g mol-1

Table 7.12: Atomic and Physical Properties of Group 18 Elements
Property	He	Ne	Ar	Kr	Xe	Rn*
Atomic number	2	10	18	36	54	86
4.00	20.18	39.95	83.80	131.30	222.00
Electronic configuration	1s²	[He]2s²2p⁶	[Ne]3s²3p⁶	[Ar]3d¹⁰4s²4p⁶	[Kr]4d¹⁰5s²5p⁶	[Xe]4f¹⁴5d¹⁰6s²6p⁶
Atomic radius/(pm)	120	160	190	200	220	–
Ionisation enthalpy, /kJ mol^-1	2372	2080	1520	1351	1170	–
Electron gain enthalpy, kJ mol^-1	48	116	96	96	77	68
Density (at STP)/gcm^-3	1.8×10^-4	9.0×10^-4	1.8×10^-3	3.7×10^-3	5.9×10^-3	8.7×10^-3
Melting point/K	–	24.6	83.8	115.9	161.3	202
Boiling point/K	4.2	27.1	87.2	119.7	165.0	211
Atmospheric content(% by volume)	5.24×10^-4	–	1.82×10^-3	0.934	1.14×10^-4	8.7×10^-6

7.23.3 Ionisation Enthalpy

Due to stable electronic configuration these gases exhibit very high ionisation enthalpy. However, it decreases down the group with increase in atomic size.

7.23.4 Atomic Radii

Atomic radii increase down the group with increase in atomic number.

7.23.5 Electron Gain Enthalpy

Since noble gases have stable electronic configurations, they have no tendency to accept the electron and therefore, have large positive values of electron gain enthalpy.

Physical Properties

All the noble gases are monoatomic. They are colourless, odourless and tasteless. They are sparingly soluble in water. They have very low melting and boiling points because the only type of interatomic interaction in these elements is weak dispersion forces. Helium has the lowest boiling point (4.2 K) of any known substance. It has an unusual property of diffusing through most commonly used laboratory materials such as rubber, glass or plastics.

Example 7.21
Noble gases have very low boiling points. Why?
Solution
Noble gases being monoatomic have no interatomic forces except weak dispersion forces and therefore, they are liquefied at very low temperatures. Hence, they have low boiling points.

Chemical Properties
In general, noble gases are least reactive. Their inertness to chemical reactivity is attributed to the following reasons:
(i) The noble gases except helium (1s² ) have completely filled ns²np⁶ electronic configuration in their valence shell.
(ii) They have high ionisation enthalpy and more positive electron gain enthalpy.
The reactivity of noble gases has been investigated occasionally, ever since their discovery, but all attempts to force them to react to form the compounds, were unsuccessful for quite a few years. In March 1962, Neil Bartlett, then at the University of British Columbia, observed the reaction of a noble gas. First, he prepared a red compound which is formulated as O₂PtF₆⁻ . He, then realised that the first ionisation enthalpy of molecular oxygen (1175 kJmol⁻¹ ) was almost identical with that of xenon (1170 kJ mol⁻¹ ). He made efforts to prepare same type of compound with Xe and was successful in preparing another red colour compound Xe⁺PtF₆⁻ by mixing PtF₆ and xenon. After this discovery, a number of xenon compounds mainly with most electronegative elements
like fluorine and oxygen, have been synthesised.

The compounds of krypton are fewer. Only the difluoride (KrF₂) has been studied in detail. Compounds of radon have not been isolated but only identified (e.g., RnF₂) by radiotracer technique. No true compounds of Ar, Ne or He are yet known.
(a) Xenon-fluorine compounds
Xenon forms three binary fluorides, XeF₂, XeF₄ and XeF₆ by the direct reaction of elements under appropriate experimental conditions.

XeF₆ can also be prepared by the interaction of XeF₄ and O₂F₂ at 143K.
XeF₄ + O₂ F₂ → XeF₆ + O₂
XeF₂, XeF₄ and XeF₆ are colourless crystalline solids and sublime readily at 298 K. They are powerful fluorinating agents. They are readily hydrolysed even by traces of water. For example, XeF₂ is hydrolysed to give Xe, HF and O₂.
2XeF₂ (s) + 2H₂O(l) → 2Xe (g) + 4 HF(aq) + O₂(g)

The structures of the three xenon fluorides can be deduced from VSEPR and these are shown in Fig. 7.9. XeF₂ and XeF₄ have linear and square planar structures respectively. XeF₆ has seven electron pairs (6 bonding pairs and one lone pair) and would, thus, have a distorted octahedral structure as found experimentally in the gas phase.

Xenon fluorides react with fluoride ion acceptors to form cationic species and fluoride ion donors to form fluoroanions.
XeF₂ + PF₅ → [XeF]⁺ [PF₆]⁻ ; XeF₄ + SbF₅ → [XeF₃]⁺ [SbF₆]⁻
XeF₆ + MF → M⁺ [XeF₇]^– (M = Na, K, Rb or Cs)

(b) Xenon-oxygen compounds
Hydrolysis of XeF₄ and XeF₆ with water gives Xe0₃.
6XeF₄ + 12 H₂O → 4Xe + 2Xe0₃ + 24 HF + 3 O₂
XeF₆ + 3 H₂O → XeO₃ + 6 HF

Partial hydrolysis of XeF₆ gives oxyfluorides, XeOF₄ and XeO₂F₂.
XeF₆ + H₂O → XeOF₄ + 2 HF
XeF₆ + 2 H₂O → XeO₂F₂ + 4HF

XeO₃ is a colourless explosive solid and has a pyramidal molecular structure (Fig. 7.9). XeOF₄ is a colourless volatile liquid and has a square pyramidal molecular structure (Fig.7.9).

Example 7.22
Does the hydrolysis of XeF₆ lead to a redox reaction?
Solution
No, the products of hydrolysis are XeOF₄ and XeO₂F₂ where the oxidation states of all the elements remain the same as it was in the reacting state.

Uses: Helium is a non-inflammable and light gas. Hence, it is used in filling balloons for meteorological observations. It is also used in gas-cooled nuclear reactors. Liquid helium (b.p. 4.2 K) finds use as cryogenic agent for carrying out various experiments at low temperatures. It is used to produce and sustain powerful superconducting magnets which form an essential part of modern NMR spectrometers and Magnetic Resonance Imaging (MRI) systems for clinical diagnosis. It is used as a diluent for oxygen in modern diving apparatus because of its very low solubility in blood.
Neon is used in discharge tubes and fluorescent bulbs for advertisement display purposes. Neon bulbs are used in botanical gardens and in green houses.
Argon is used mainly to provide an inert atmosphere in high temperature metallurgical processes (arc welding of metals or alloys) and for filling electric bulbs. It is also used in the laboratory for handling substances that are air-sensitive. There are no significant uses of Xenon and Krypton. They are used in light bulbs designed for special purposes.

Intext Question
7.32 Why is helium used in diving apparatus?
7.33 Balance the following equation: XeF₆ + H₂O → XeO₂F₂ + HF
7.34 Why has it been difficult to study the chemistry of radon?

Summary

Groups 13 to 18 of the periodic table consist of p-block elements with their valence shell electronic configuration ns²np^1–6. Groups 13 and 14 were dealt with in Class XI. In this Unit remaining groups of the p-block have been discussed.

Group 15 consists of five elements namely, N, P, As, Sb and Bi which have general electronic configuration ns²np³. Nitrogen differs from other elements of this group due to small size, formation of pπ–pπ multiple bonds with itself and with highly electronegative atom like O or C and non-availability of d orbitals to expand its valence shell. Elements of group 15 show gradation in properties. They react with oxygen, hydrogen and halogens. They exhibit two important oxidation states, + 3 and + 5 but +3 oxidation is favoured by heavier elements due to ‘inert pair effect’.

Dinitrogen can be prepared in laboratory as well as on industrial scale. It forms oxides in various oxidation states as N₂O, NO, N₂O₃, NO₂, N₂O₄ and N₂O₅. These oxides have resonating structures and have multiple bonds. Ammonia can be prepared on large scale by Haber’s process. HNO₃ is an important industrial chemical. It is a strong monobasic acid and is a powerful oxidising agent. Metals and non-metals react with HNO₃ under different conditions to give NO or NO₂.

Phosphorus exists as P₄ in elemental form. It exists in several allotropic forms. It forms hydride, PH₃ which is a highly poisonous gas. It forms two types of halides as PX₃ and PX₅. PCl₃ is prepared by the reaction of white phosphorus with dry chlorine while PCl₅ is prepared by the reaction of phosphorus with SO₂Cl₂. Phosphorus forms a number of oxoacids. Depending upon the number of P–OH groups, their basicity varies. The oxoacids which have P–H bonds are good reducing agents.

The Group 16 elements have general electronic configuration ns²np⁴. They show maximum oxidation state, +6. Gradation in physical and chemical properties is observed in the group 16 elements. In laboratory, dioxygen is prepared by heating KClO₃ in presence of MnO₂. It forms a number of oxides with metals. Allotropic form of oxygen is O₃ which is a highly oxidising agent. Sulphur forms a number of allotropes. Of these, α– and β– forms of sulphur are the most important. Sulphur combines with oxygen to give oxides such as SO₂ and SO₃. SO₂ is prepared by the direct union of sulphur with oxygen. SO₂ is used in the manufacture of H₂SO₄. Sulphur forms a number of oxoacids. Amongst them, the most important is H₂SO₄. It is prepared by contact process. It is a dehydrating and oxidising agent. It is used in the manufacture of several compounds.

Group 17 of the periodic table consists of the following elements F, Cl, Br, I and At.These elements are extremely reactive and as such they are found in the combined state only. The common oxidation state of these elements is –1. However, highest oxidation state can be +7. They show regular gradation in physical and chemical properties. They form oxides, hydrogen halides, interhalogen compounds and oxoacids. Chlorine is conveniently obtained by the reaction of HCl with KMnO₄. HCl is prepared by heating NaCl with concentrate H₂SO₄. Halogens combine with one another to form interhalogen compounds of the type XX¹_n (n = 1, 3, 5, 7) where X¹ is lighter than X. A number of oxoacids of halogens are known. In the structures of these oxoacids, halogen is the central atom which is bonded in each case with one OH bond as X–OH. In some cases X = 0 bonds are also found.

Group 18 of the periodic table consists of noble gases. They have ns² np⁶ valence shell electronic configuration except He which has 1s². All the gases except Rn occur in atmosphere. Rn is obtained as the decay product of ²²⁶Ra.

Due to complete octet of outermost shell, they have less tendency to form compounds. The best characterised compounds are those of xenon with fluorine and oxygen only under certain conditions. These gases have several uses. Argon is used to provide inert atmosphere, helium is used in filling balloons for meteorological observations, neon is used in discharge tubes and fluorescent bulbs.

Exercises
7.1 Discuss the general characteristics of Group 15 elements with reference to their electronic configuration, oxidation state, atomic size, ionisation enthalpy and electronegativity.
7.2 Why does the reactivity of nitrogen differ from phosphorus?
7.3 Discuss the trends in chemical reactivity of group 15 elements.
7.4 Why does NH₃ form hydrogen bond but PH₃ does not?
7.5 How is nitrogen prepared in the laboratory? Write the chemical equations of the reactions involved.
7.6 How is ammonia manufactured industrially?
7.7 Illustrate how copper metal can give different products on reaction with HNO₃.
7.8 Give the resonating structures of NO₂ and N₂O₅.
7.9 The HNH angle value is higher than HPH, HAsH and HSbH angles. Why? [Hint: Can be explained on the basis of sp³ hybridisation in NH³ and only s–p bonding between hydrogen and other elements of the group].
7.10 Why does R₃P = O exist but R₃N = O does not (R = alkyl group)?
7.11 Explain why NH₃ is basic while BiH₃ is only feebly basic.
7.12 Nitrogen exists as diatomic molecule and phosphorus as P₄. Why?
7.13 Write main differences between the properties of white phosphorus and red phosphorus.
7.14 Why does nitrogen show catenation properties less than phosphorus?
7.15 Give the disproportionation reaction of H₃PO₃.
7.16 Can PCl₅ act as an oxidising as well as a reducing agent? Justify.
7.17 Justify the placement of O, S, Se, Te and Po in the same group of the periodic table in terms of electronic configuration, oxidation state and hydride formation.
7.18 Why is dioxygen a gas but sulphur a solid?
7.19 Knowing the electron gain enthalpy values for O → O⁻ and O → O²⁻ as –141
and 702 kJ mol⁻¹ respectively, how can you account for the formation of a large number of oxides having O species and not O ?
(Hint: Consider lattice energy factor in the formation of compounds).
7.20 Which aerosols deplete ozone?
7.21 Describe the manufacture of H₂SO₄ by contact process?
7.22 How is SO₂ an air pollutant?
7.23 Why are halogens strong oxidising agents?
7.24 Explain why fluorine forms only one oxoacid, HOF.
7.25 Explain why inspite of nearly the same electronegativity, nitrogen forms hydrogen bonding while chlorine does not.
7.26 Write two uses of ClO₂.
7.27 Why are halogens coloured?
7.28 Write the reactions of F₂ and Cl₂ with water.
7.29 How can you prepare Cl₂ from HCl and HCl from Cl₂? Write reactions only.
7.30 What inspired N. Bartlett for carrying out reaction between Xe and PtF₆?
7.31 What are the oxidation states of phosphorus in the following:
(i)H₃PO₃
(ii) PCl₃
(iii) Ca₃P₂
(iv) Na₃PO₄
(v) POF₃?
7.32 Write balanced equations for the following:
(i) NaCl is heated with sulphuric acid in the presence of MnO₂.
(ii) Chlorine gas is passed into a solution of NaI in water.
7.33 How are xenon fluorides XeF₂, XeF₄ and XeF₆ obtained?
7.34 With what neutral molecule is ClO isoelectronic? Is that molecule a Lewis base?
7.35 How are XeO₃ and XeOF₄ prepared?
7.36 Arrange the following in the order of property indicated for each set:
(i) F₂, Cl₂, Br₂, I₂ – increasing bond dissociation enthalpy.
(ii) HF, HCl, HBr, HI – increasing acid strength.
(iii) NH₃, PH₃, AsH₃, SbH₃, BiH₃ – increasing base strength.
7.37 Which one of the following does not exist?
(i) XeOF₄
(ii) NeF₂
(iii) XeF₂
(iv) XeF₆
7.38 Give the formula and describe the structure of a noble gas species which is isostructural with:
(i) ICl₄^–
(ii) IBr₂^–
(iii) BrO₃^–
7.39 Why do noble gases have comparatively large atomic sizes?
7.40 List the uses of neon and argon gases.
Answers to Some Intext Questions
7.1 Higher the positive oxidation state of central atom, more will be its polarising power which, in turn, increases the covalent character of bond formed between the central atom and the other atom.
7.2 Because BiH₃ is the least stable among the hydrides of Group 15.
7.3 Because of strong pπ–pπ overlap resulting into the triple bond, N≡N.
7.6 From the structure of N₂O₅ it is evident that covalence of nitrogen is four.
7.7 Both are sp³ hybridised. In PH₄⁺ all the four orbitals are bonded whereas in PH₃ there is a lone pair of electrons on P, which is responsible for lone pair-bond pair repulsion in PH₃ reducing the bond angle to less than 109° 28′.
7.10 PCl₅ + D₂O → POCl₃ + 2DCl
7.11 Three P–OH groups are present in the molecule of H₃PO₄. Therefore, its basicity is three.
7.15 Because of small size and high electronegativity of oxygen, molecules of water are highly associated through hydrogen bonding resulting in its liquid state.
7.21 Both the S–O bonds are covalent and have equal strength due to resonating structures.
7.25 H₂SO₄ is a very strong acid in water largely because of its first ionisation to H₃O⁺ and HSO₄^–. The ionisation of HSO₄^– to H₃O⁺ and SO₄^2– is very very small. That is why K _a2 << K _a1 .
7.31 In general, interhalogen compounds are more reactive than halogens due to weaker X–X¹ bonding than X–X bond. Thus, ICl is more reactive than I₂.
7.34 Radon is radioactive with very short half-life which makes the study of chemistry of radon difficult.

I. Multiple Choice Questions (Type-I)

1. On addition of conc. H₂SO4 to a chloride salt, colourless fumes are evolved but in case of iodide salt, violet fumes come out. This is because

(i) H₂SO4 reduces HI to I₂
(ii) HI is of violet colour
(iii) HI gets oxidised to I₂
(iv) HI changes to HIO₃

2. In qualitative analysis when H₂S is passed through an aqueous solution of salt acidified with dil. HCl, a black precipitate is obtained. On boiling the precipitate with dil. HNO₃, it forms a solution of blue colour. Addition of excess of aqueous solution of ammonia to this solution gives _________.

(i) deep blue precipitate of Cu(OH)₂
(ii) deep blue solution of [Cu(NH₃)₄]²⁺
(iii) deep blue solution of Cu(NO₃)₂
(iv) deep blue solution of Cu(OH)₂.Cu(NO₃)₂

3. In a cyclotrimetaphosphoric acid molecule, how many single and double bonds are present?

(i) 3 double bonds; 9 single bonds
(ii) 6 double bonds; 6 single bonds
(iii) 3 double bonds; 12 single bonds
(iv) Zero double bonds; 12 single bonds

4. Which of the following elements can be involved in pπ–dπ bonding?

(i) Carbon
(ii) Nitrogen
(iii) Phosphorus
(iv) Boron

5. Which of the following pairs of ions are isoelectronic and isostructural?

(i) CO₃^2–, NO₃^–
(ii) ClO₃^– , CO₃^2–
(iii) SO₃^2–, NO₃^–
(iv) ClO₃^– , SO₃^2–

6. Affinity for hydrogen decreases in the group from fluorine to iodine. Which of the halogen acids should have highest bond dissociation enthalpy?

(i) HF
(ii) HCl
(iii) HBr
(iv) HI

7. Bond dissociation enthalpy of E—H (E = element) bonds is given below. Which of the compounds will act as strongest reducing agent?

Compound	NH₃	PH₃	AsH₃	SbH₃
Δ_diss(E—H)/kJ mol^–1	389	322	297	255

(i) NH₃
(ii) PH₃
(iii) AsH₃
(iv) SbH₃

8. On heating with concentrated NaOH solution in an inert atmosphere of CO₂, white phosphorus gives a gas. Which of the following statement is incorrect about the gas?

(i) It is highly poisonous and has smell like rotten fish.
(ii) It’s solution in water decomposes in the presence of light.
(iii) It is more basic than NH₃.
(iv) It is less basic than NH₃.

9. Which of the following acids forms three series of salts?

(i) H₃PO₂
(ii) H₃BO₃
(iii) H₃PO₄
(iv) H₃PO₃

10. Strong reducing behaviour of H₃PO₂ is due to

(i) Low oxidation state of phosphorus
(ii) Presence of two –OH groups and one P–H bond
(iii) Presence of one –OH group and two P–H bonds
(iv) High electron gain enthalpy of phosphorus

11. On heating lead nitrate forms oxides of nitrogen and lead. The oxides formed are ______.

(i) N₂O, PbO
(ii) NO₂, PbO
(iii) NO, PbO
(iv) NO, PbO₂

12. Which of the following elements does not show allotropy?

(i) Nitrogen
(ii) Bismuth
(iii) Antimony
(iv) Arsenic

13. Maximum covalency of nitrogen is ______________.

(i) 3
(ii) 5
(iii) 4
(iv) 6

14. Which of the following statements is wrong?

(i) Single N–N bond is stronger than the single P–P bond.
(ii) PH₃ can act as a ligand in the formation of coordination compound with transition elements.
(iii) NO₂ is paramagnetic in nature.
(iv) Covalency of nitrogen in N₂O₅ is four.

15. A brown ring is formed in the ring test for NO₃^– ion. It is due to the formation of

(i) [Fe(H₂O)₅(NO)]²⁺
(ii) FeSO₄.NO₂
(iii) [Fe(H₂O)₄(NO)₂]²⁺
(iv) FeSO₄.HNO₃

16. Elements of group-15 form compounds in +5 oxidation state. However, bismuth forms only one well characterised compound in +5 oxidation state. The compound is

(i) Bi₂O₅
(ii) BiF₅
(iii) BiCl₅
(iv) Bi₂S₅

17. On heating ammonium dichromate and barium azide separately we get

(i) N₂ in both cases
(ii) N₂2 with ammonium dichromate and NO with barium azide
(iii) N₂O with ammonium dichromate and N₂ with barium azide
(iv) N₂O with ammonium dichromate and NO₂ with barium azide
18. In the preparation of HNO3, we get NO gas by catalytic oxidation of ammonia.

The moles of NO produced by the oxidation of two moles of NH₃ will be ______.

(i) 2
(ii) 3
(iii) 4
(iv) 6

19. The oxidation state of central atom in the anion of compound NaH₂PO₂ will be ______.

(i) +3
(ii) +5
(iii) +1
(iv) –3

20. Which of the following is not tetrahedral in shape?

(i) NH₄⁺
(ii) SiCl₄
(iii) SF₄
(iv) SO₄^2–

21. Which of the following are peroxoacids of sulphur?

(i) H₂SO₅ and H₂S₂O₈
(ii) H₂SO₅ and H₂S₂O₇
(iii) H₂S₂O₇ and H₂S₂O₈
(iv) H₂S₂O₆ and H₂S₂O₇

22. Hot conc. H₂SO₄ acts as moderately strong oxidising agent. It oxidises both metals and nonmetals. Which of the following element is oxidised by conc. H₂SO₄ into two gaseous products?

(i) Cu
(ii) S
(iii) C
(iv) Zn

23. A black compound of manganese reacts with a halogen acid to give greenish yellow gas. When excess of this gas reacts with NH₃ an unstable trihalide is formed. In this process the oxidation state of nitrogen changes from _________.

(i) – 3 to +3
(ii) – 3 to 0
(iii) – 3 to +5
(iv) 0 to – 3

24. In the preparation of compounds of Xe, Bartlett had taken O₂⁺ Pt F₆^– as a base compound. This is because

(i) both O₂ and Xe have same size.
(ii) both O₂ and Xe have same electron gain enthalpy.
(iii) both O₂ and Xe have almost same ionisation enthalpy.
(iv) both Xe and O₂ are gases.

25. In solid state PCl₅ is a _________.

(i) covalent solid
(ii) octahedral structure
(iii) ionic solid with [PCl₆]⁺ octahedral and [PCl₄]^– tetrahedra
(iv) ionic solid with [PCl₄]⁺ tetrahedral and [PCl₆]^– octahedra

26. Reduction potentials of some ions are given below. Arrange them in decreasing order of oxidising power.

Ion	ClO₄^–	IO₄^–	BrO₄^–
Reduction potential E^Θ/V	E^Θ=1.19V	E^Θ=1.65V	E^Θ=1.74V

(i) ClO₄^– > IO₄^– > BrO₄^–
(ii) IO₄^– > BrO₄^– > ClO₄^–
(iii) BrO₄^– > IO₄^– > ClO₄^––
(iv) BrO₄^– > ClO₄^– > IO₄^–

27. Which of the following is isoelectronic pair?

(i) ICl₂, ClO₂
(ii) BrO₂^– , BrF₂⁺
(iii) ClO₂, BrF
(iv) CN^–, O₃

II. Multiple Choice Questions (Type-II)

Note : In the following questions two or more options may be correct.

28. If chlorine gas is passed through hot NaOH solution, two changes are observed in the oxidation number of chlorine during the reaction. These are ________ and _________.

(i) 0 to +5
(ii) 0 to +3
(iii) 0 to –1
(iv) 0 to +1

29. Which of the following options are not in accordance with the property mentioned against them?

(i) F₂ > Cl₂ > Br₂ > I₂ Oxidising power.
(ii) MI > MBr > MCl > MF Ionic character of metal halide.
(iii) F₂ > Cl₂ > Br₂ > I₂ Bond dissociation enthalpy.
(iv) HI < HBr < HCl < HF Hydrogen-halogen bond strength.

30. Which of the following is correct for P₄ molecule of white phosphorus?

(i) It has 6 lone pairs of electrons.
(ii) It has six P–P single bonds.
(iii) It has three P–P single bonds.
(iv) It has four lone pairs of electrons.

31. Which of the following statements are correct?

(i) Among halogens, radius ratio between iodine and fluorine is maximum.
(ii) Leaving F—F bond, all halogens have weaker X—X bond than X—X’ bond in interhalogens.
(iii) Among interhalogen compounds maximum number of atoms are present in iodine fluoride.
(iv) Interhalogen compounds are more reactive than halogen compounds.

32. Which of the following statements are correct for SO₂ gas?

(i) It acts as bleaching agent in moist conditions.
(ii) It’s molecule has linear geometry.
(iii) It’s dilute solution is used as disinfectant.
(iv) It can be prepared by the reaction of dilute H₂SO₄ with metal sulphide.

33. Which of the following statements are correct?

(i) All the three N—O bond lengths in HNO₃ are equal.
(ii) All P—Cl bond lengths in PCl₅ molecule in gaseous state are equal.
(iii) P₄ molecule in white phohsphorus have angular strain therefore white phosphorus is very reactive.
(iv) PCl is ionic in solid state in which cation is tetrahedral and anion is octahedral.

34. Which of the following orders are correct as per the properties mentioned against each?

(i) As₂O₃ < SiO₂ < P₂O₃ < SO₂ Acid strength.
(ii) AsH₃ < PH₃ < NH₃ Enthalpy of vapourisation.
(iii) S < O < Cl < F More negative electron gain enthalpy.
(iv) H₂O > H₂S > H₂Se > H₂Te Thermal stability.

35. Which of the following statements are correct?

(i) S–S bond is present in H₂S₂O₆.
(ii) In peroxosulphuric acid (H₂SO₅) sulphur is in +6 oxidation state.
(iii) Iron powder along with Al₂O₃ and K₂O is used as a catalyst in the preparation of NH₃ by Haber’s process.
(iv) Change in enthalpy is positive for the preparation of SO₃ by catalytic oxidation of SO₂.

36. In which of the following reactions conc. H₂SO₄ is used as an oxidising reagent?

(i) CaF₂ + H₂SO₄ → CaSO₄ + 2HF
(ii) 2HI + H₂SO₄ → I₂ + SO₂ + 2H₂O
(iii) Cu + 2H₂SO₄ → CuSO₄ + SO₂ + 2H₂O
(iv) NaCl + H₂SO₄ → NaHSO₄ + HCl

37. Which of the following statements are true?

(i) Only type of interactions between particles of noble gases are due to weak dispersion forces.
(ii) Ionisation enthalpy of molecular oxygen is very close to that of xenon.
(iii) Hydrolysis of XeF₆ is a redox reaction.
(iv) Xenon fluorides are not reactive.

III. Short Answer Type

38. In the preparation of H₂SO₄ by Contact Process, why is SO₃ not absorbed directly in water to form H₂SO₄?
39. Write a balanced chemical equation for the reaction showing catalytic oxidation of NH₃ by atmospheric oxygen.
40. Write the structure of pyrophosphoric acid.
41. PH₃ forms bubbles when passed slowly in water but NH₃ dissolves. Explain why?
42. In PCl₅, phosphorus is in sp³d hybridised state but all its five bonds are not equivalent. Justify your answer with reason.
43. Why is nitric oxide paramagnetic in gaseous state but the solid obtained on cooling it is diamagnetic?
44. Give reason to explain why ClF₃ exists but FCl₃ does not exist.
45. Out of H₂O and H₂S, which one has higher bond angle and why?
46. SF6 is known but SCl₆ is not. Why?
47. On reaction with Cl₂, phosphorus forms two types of halides ‘A’ and ‘B’. Halide A is yellowish-white powder but halide ‘B’ is colourless oily liquid. Identify A and B and write the formulas of their hydrolysis products.
48. In the ring test of NO₃^– ion, Fe²⁺ ion reduces nitrate ion to nitric oxide, which
combines with Fe²⁺ (aq) ion to form brown complex. Write the reactions involved in the formation of brown ring.
49. Explain why the stability of oxoacids of chlorine increases in the order given below:
HClO < HClO₂ < HClO₃ < HClO₄
50. Explain why ozone is thermodynamically less stable than oxygen.
51. P4O6 reacts with water according to equation P₄O₆ + 6H₂O → 4H₃PO₃. Calculate the volume of 0.1 M NaOH solution required to neutralise the acid formed by dissolving 1.1 g of P₄O₆ in H₂O.
52. White phosphorus reacts with chlorine and the product hydrolyses in the presence of water. Calculate the mass of HCl obtained by the hydrolysis of the product formed by the reaction of 62 g of white phosphorus with chlorine in
the presence of water.
53. Name three oxoacids of nitrogen. Write the disproportionation reaction of that oxoacid of nitrogen in which nitrogen is in +3 oxidation state.
54. Nitric acid forms an oxide of nitrogen on reaction with P₄O₁₀. Write the reaction involved. Also write the resonating structures of the oxide of nitrogen formed.
55. Phosphorus has three allotropic forms — (i) white phosphorus (ii) redb phosphorus and (iii) black phosphorus. Write the difference between white and red phosphorus on the basis of their structure and reactivity.
56. Give an example to show the effect of concentration of nitric acid on the formation of oxidation product.
57. PCl₅ reacts with finely divided silver on heating and a white silver salt is obtained, which dissolves on adding excess aqueous NH₃ solution. Write the reactions involved to explain what happens.
58. Phosphorus forms a number of oxoacids. Out of these oxoacids phosphinic acid has strong reducing property. Write its structure and also write a reaction showing its reducing behaviour.

IV. Matching Type

Note : Match the items of Column I and Column II in the following questions.

59. Match the compounds given in Column I with the hybridisation and shape given in Column II and mark the correct option.

	Column I		Column II
(A)	Xe F₆	(1)	sp³d³ – distorted octahedral
(B)	Xe O₃	(2)	sp³d² – square planar
(C)	Xe OF₄	(3)	sp³ – pyramidal
(D)	Xe F₄	(4)	sp³ d² – square pyramidal

Code :

(i) A(1) B(3) C(4) D(2)
(ii) A(1) B(2) C(4) D(3)
(iii) A(4) B(3) C(1) D(2)
(iv) A(4) B(1) C(2) D(3)

60. Match the formulas of oxides given in Column I with the type of oxide given in Column II and mark the correct option.

	Column I		Column II
(A)	Pb₃O₄	(1)	Neutral oxide
(B)	N₂O	(2)	Acidic oxide
(C)	Mn₂O₇	(3)	Basic oxide
(D)	Bi₂O₃	(4)	Mixed oxide

Code :

(i) A(1) B(2) C(3) D(4)
(ii) A(4) B(1) C(2) D(3)
(iii) A(3) B(2) C(4) D(1)
(iv) A(4) B(3) C(1) D(2)

61. Match the items of Columns I and II and mark the correct option.

	Column I		Column II
(A)	H₂SO₄	(1)	Highest electron gain enthalpy
(B)	CCl₃NO₂	(2)	Chalcogen
(C)	Cl₂	(3)	Tear gas
(D)	Sulphur	(4)	Storage batteries

Code :

(i) A(4) B(3) C(1) D(2)
(ii) A(3) B(4) C(1) D(2)
(iii) A(4) B(1) C(2) D(3)
(iv) A(2) B(1) C(3) D(4)

62. Match the species given in Column I with the shape given in Column II and mark the correct option.

	Column I		Column II
(A)	SF₄	(1)	Tetrahedral
(B)	BrF₃(2)	Pyramidal
(C)	BrO₃^–	(3)	Sea-saw shaped
(D)	NH₄⁺	(4)	Bent T-shaped

Code :

(i) A (3) B (2) C (1) D (4)
(ii) A (3) B (4) C (2) D (1)
(iii) A (1) B (2) C (3) D (4)
(iv) A (1) B (4) C (3) D (2)

63. Match the items of Columns I and II and mark the correct option.

	Column I		Column II
(A)	Its partial hydrolysis does not change oxidation state of central atom	(1)	He
(B)	It is used in modern diving apparatus	(2)	XeF₆
(C)	It is used to provide inert atmosphere for filling electrical bulbs	(3)	XeF₄
(D)	Its central atom is in sp³d² hybridisation	(4)	Ar

Code :

(i) A (1) B (4) C (2) D (3)
(ii) A (1) B (2) C (3) D (4)
(iii) A (2) B (1) C (4) D (3)
(iv) A (1) B (3) C (2) D (4)

V. Assertion and Reason Type

Note : In the following questions a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.

(i) Both assertion and reason are correct statements, and reason is the correct explanation of the assertion.
(ii) Both assertion and reason are correct statements, but reason is not the correct explanation of the assertion.
(iii) Assertion is correct, but reason is wrong statement.
(iv) Assertion is wrong but reason is correct statement.
(v) Both assertion and reason are wrong statements.

64. Assertion : N₂ is less reactive than P₄.
Reason : Nitrogen has more electron gain enthalpy than phosphorus.

65. Assertion : HNO₃ makes iron passive.
Reason : HNO₃ forms a protective layer of ferric nitrate on the surface of iron.

66. Assertion : HI cannot be prepared by the reaction of KI with concentrated H₂SO₄
Reason : HI has lowest H–X bond strength among halogen acids.

67. Assertion : Both rhombic and monoclinic sulphur exist as S₈ but oxygen exists as O₂.
Reason : Oxygen forms pπ – pπ multiple bond due to small size and small bond length but pπ – pπ bonding is not possible in sulphur.

68. Assertion : NaCl reacts with concentrated H₂SO₄ to give colourless fumes with pungent smell. But on adding MnO₂ the fumes become greenish yellow.
Reason : MnO₂ oxidises HCl to chlorine gas which is greenish yellow.

69. Assertion : SF₆ cannot be hydrolysed but SF₄ can be.
Reason : Six F atoms in SF₆ prevent the attack of H₂O on sulphur atom of SF₆.

VI. Long Answer Type

70. An amorphous solid “A” burns in air to form a gas “B” which turns lime water milky. The gas is also produced as a by-product during roasting of sulphide ore. This gas decolourises acidified aqueous KMnO₄ solution and reduces Fe³⁺ to Fe²⁺. Identify the solid “A” and the gas “B” and write the reactions involved.

71. On heating lead (II) nitrate gives a brown gas “A”. The gas “A” on cooling changes to colourless solid “B”. Solid “B” on heating with NO changes to a blue solid ‘C’. Identify ‘A’, ‘B’ and ‘C’ and also write reactions involved and
draw the structures of ‘B’ and ‘C’.

72. On heating compound (A) gives a gas (B) which is a constituent of air. This gas when treated with 3 mol of hydrogen (H₂) in the presence of a catalyst gives another gas (C) which is basic in nature. Gas C on further oxidation in moist condition gives a compound (D) which is a part of acid rain. Identify compounds (A) to (D) and also give necessary equations of all the steps involved.

ANSWERS

I. Multiple Choice Questions (Type-I)

1. (iii) 2. (ii) 3. (i) 4. (iii) 5. (i) 6. (i) 7. (iv) 8. (iii) 9. (iii) 10. (iii) 11. (ii) 12. (i) 13. (iii) 14. (i) 15. (i) 16. (ii) 17. (i) 18. (i) 19. (iii) 20. (iii) 21. (i) 22. (iii) 23. (i) 24. (iii) 25. (iv) 26. (iii) 27. (ii)

II. Multiple Choice Questions (Type-II)

28. (i), (iii) 29. (ii), (iii) 30. (ii), (iv) 31. (i), (iii), (iv) 32. (i), (iii) 33. (iii), (iv) 34. (i), (iv) 35. (i), (ii) 36. (ii), (iii) 37. (i), (ii)

III. Short Answer Type

38. Acid fog is formed, which is difficult to condense.

39.

40.
Pyrophosphoric acid

41. NH₃ forms hydrogen bonds with water therefore it is soluble in it but PH₃ cannot form hydrogen bond with water so it escapes as gas.
42. [Hint : It has trigonal bipyramidal geometry]
43. In gaseous state NO₂ exists as monomer which has one unpaired electron but in solid state it dimerises to N₂O₄ so no unpaired electron is left hence solid form is diamagnetic.
44. Because fluorine is more electronegative as compared to chlorine.
45. Bond angle of H₂O is larger, because oxygen is more electronegative than sulphur therefore bond pair electron of O–H bond will be closer to oxygen and there will be more bond-pair bond-pair repulsion between bond pairs
of two O–H bonds.
46. Due to small size of fluorine six F^– ion can be accomodated around sulphur whereas chloride ion is comparatively larger in size, therefore, there will be interionic repulsion.

47. A is PCl₅ (It is yellowish white powder)
P₄ + 10Cl₂ → 4PCl₅
B is PCl₃ (It is a colourless oily liquid)
P₄ + 6Cl₂ → 4PCl₃

Hydrolysis products are formed as follows :

PCl₃ + 3H₂O → H₃PO₃ + 3HCl
PCl₅ + 4H₂O → H₃PO₄ + 5HCl

48. NO₃^– + 3Fe²⁺ + 4H⁺ → NO + 3Fe³⁺ + 2H₂O
[Fe(H₂O)₆]²⁺ + NO → [Fe(H₂O)₅(NO)]²⁺ + H2O
(brown complex)

49. Oxygen is more electronegative than chlorine, therefore dispersal of negative charge present on chlorine increases from ClO^– to ClO₄^– ion because number of oxygen atoms attached to chlorine is increasing. Therefore, stability of ions will increase in the order given below :

ClO^– < ClO₂^– < ClO₃^– < ClO₄^–

Thus due to increase in stability of conjugate base, acidic strength of corresponding acid increases in the following order HClO < HClO₂ < HClO₃ < HClO₄

50. See the NCERT textbook for Class XII, page 186.
51. P₄O₆ + 6H₂O → 4H₃PO₃
H₃PO₃ + 2NaOH → Na₂HPO₃ + 2H₂O] x 4 (Neutralisation reaction)
P₄O₆ + 8NaOH → 4Na₂HPO₄ + 2H₂O
1 mol 8 mol
Product formed by 1 mol of P₄O₆ is neutralised by 8 mols of NaOH
∴ Product formed by 1.1/220 mol of P₄O₆ will be neutralised by 1.1×8/220 mol of NaOH
Molarity of NaOH solution is 0.1M
⇒ 0.1 mol NaOH is present in 1 L solution
∴1.1×8/220 mol NaOH is present in (1.1 x 8/220 x 0.1)L = 88/220 L = 4/10 L = 0.4 L = 400 mL of NaOH solution.

52. P₄ + 6Cl₂ → 4PCl₃
PCl₃ + 3H₂O → H₃PO₃ + 3HCl] x 4
P₄ + 6Cl₂ + 12H₂O → 4H₃PO₃ + 12HCl
1 mol of white phosphorus produces 12 mol of HCl
62g of white phosphorus has been taken which is equivalent to 62/124 = 1/2 mol.
Therefore 6 mol HCl will be formed.
Mass of 6 mol HCl = 6 x 36.5 = 219.0 g HCl

53. Three oxoacids of nitrogen are
(i) HNO₂, Nitrous acid
(ii) HNO₃ , Nitric acid
(iii) Hyponitrous acid, H₂N₂O₂

54. 4HNO₃ + P4O₁₀ → 4HPO₃ + 2N₂O₅

55. (a) • Structures (See NCERT textbook for Class XII)
• White phosphorus is discrete tetrahedral molecule. Thus it has tetrahedral structure with six P–P bonds.
• Red phosphorus has polymeric structure in which P₄ tetrahedra are linked together through P—P bonds to form chain.
(b) Reactivity
White phosphorus is much more reactive than red phosphorus. This is because in white phosphorus there is angular strain in P₄ molecules because the bond angles are only of 60°.

56. Dilute and concentrated nitric acid give different oxidation products on reaction with copper metal.
3Cu + 8HNO₃ (dil.) → 3Cu(NO₃)₂ + 2NO + 4H₂O
Cu + 4HNO₃ (Conc.) → 3Cu(NO₃)₂ + 2NO + 2H₂O

57. PCl₅ + 2Ag → 2AgCl + PCl₃
AgCl + 2NH₃(aq) → [Ag(NH₃)₂]+Cl^–
(soluble complex)

58. Structure of phosphinic acid (Hypophosphorous acid) is as follows :

Reducing behaviour of phosphinic acid is observable in the reaction with silver nitrate given below :
4AgNO₃ + 2H₂O + H₃PO₂ → 4Ag + 4HNO₃ + H₃PO₄

IV. Matching Type

59. (i) 60. (ii) 61. (i) 62. (ii) 63. (iii)

V. Assertion and Reason Type

64. (iii) 65. (iii) 66. (ii) 67. (i) 68. (i) 69. (i)

VI. Long Answer Type

70. ‘A’ is S₈ ‘B’ is SO₂ gas

2MnO₄^– + 5SO₂ + 2H₂O → 5SO₄^2– + 4H⁺ + 2Mn²⁺
(violet) (colourless)
2Fe³⁺ + SO₂ + 2H₂O → 2Fe²⁺ + SO₄^2– + 4H⁺

71.

72. A = NH₄NO₂ B = N₂ C = NH₃ D = HNO₃
(i) NH₄NO₂ → N₂ + 2H₂O
(ii) N₂ + 3H₂ → 2NH₃
(iii) 4NH₃ + 5O₂ → 4NO + 6H₂O
4NO + O₂ → 2NO₂
3NO₂ + H₂O → 2HNO₃ + NO

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Simplified Knowledge Management Classes

Must see https://zookeepersblog.wordpress.com/some-points-which-i-wish-all-my-new-prospective-students-know/
🙂
Do you want to make money working at home ?
see http://skmclasses.weebly.com/jobs.html
–
search for videos in http://www.skmclasses.kinja.com

you will get most videos. I say most because I do not upload all videos that I make. I have many more videos which are not in the net.

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The following Videos are available for you ( As of Now ). These explain tricky Physics and Mathematics Numericals.

Eventually I will try to give Videos for full course here for you.

These covers PU ( Pre University courses, school / college ) courses, IIT JEE, AIEEE ( All India Engineering Entrance Examination ) , CET ( Combined Engineering Test ), AIPMT ( All India Pre Medical Test ), ISc ( Intermediate Science / Indian School Certificate Exam ), CBSE ( Central Board Secondary Exam ), Roorkey Joint Entrance Test Questions ( Discontinued since 2002 ), APhO ( Asian Physics Olympiad ), IPhO ( International Physics Olympiad ), IMO ( International Mathematics Olympiad ) , NSEP ( National Standard Exam in Physics ), RMO ( Regional Math Olympiad , India ), INMO ( Indian National Maths Olympiad ), Irodov Solutions, Prof. H C Verma ( Concepts of Physics ) Solutions etc.

( You can see the history of Indian Participation in various Olympiads at ->
https://zookeepersblog.wordpress.com/indian-participation-in-ipho-icho-ibo-and-astronomy-olympiad/ )

[ In each of these videos there is at-least 1 or more errors. Please tell me about those ]

search for videos in http://www.skmclasses.kinja.com
You should get to see all the Uploaded videos. Though we have many more study videos.

Thanks and Regards
Zookeeper ;-D Subhashish Chattopadhyay

[ I suggest you see the videos starting with 1- first then starting with 2- ….. in that sequence. ]

[ Tell your friends about this link if you liked the videos ]

In case of doubts or suggestions, Please send me email at mokshya@gmail.com

search for videos in http://www.skmclasses.kinja.com

Answers to -> Frequently Asked Questions ( FAQ ) [ commonly asked intelligent Questions 🙂 ]

1 ) How do I prepare for IIT ?

Ans : – See the videos made by me ( search for videos in http://www.skmclasses.kinja.com
Though we have many more which have not been uploaded ). While watching the videos, take notes and try to solve the problems yourself by pausing the video. Tell me if any calculation is wrong. See the videos with 1- first then 2- and so on. Write to IAPT Kothrud, Pune office to buy ( 150 Rs approx ) the book with previous papers of NSEP ( National Standard Exam in Physics – The 1st level ), INPhO ( Indian National Physics Olympiad – 2nd level ). Prepare with these and see how much you are scoring. You can guess your ALL INDIA rank easily from NSEP, and INPhO rank. Since 1998 the IIT JEE toppers have been mostly representing India in IPhO.

2 ) Which codec and Player do I use to see the videos ?

Ans : – You can use GOM Player, or VLC Player. You have to have good speakers with filters or good earphones with filters. We have checked mostly it is OK with these. ( If you are depending only on your embedded speakers of computer /screen / keyboard then there may be extra distortions. As these speakers are often not of good Quality. Also install latest KL Codecs ) In any case reduce the volume see the board, imagine sitting in the last bench and solving the problems of your own. See if your solution differs anywhere with the scribbles on the board.

3 ) Why are you giving these ( high Quality ) lecture for free ?

Ans : Well there are lot of good things free in this world. Linux, My-SQL, Open-Office ….. Go to sourceforge and get thousands of high quality software free along with source code. Yes all officially free …. Why do you think Richard Stallman, Zimmerman, ….. etc are considered Guru philosophers ? In Punjab and Gurudwaras worldwide there are so many Langars where you get better food than Restaurants. ….. why ? Why do you have Dharmasalas and subsidized rest rooms near hospitals / Famous Temples / various places ? in Iftar party anyone can eat for free …. why ?

I am teaching since 1989 I have observed most students can do much better if they have the self motivation to solve and practice. Cheap books are available in second hand bookstalls, where you get thousands of Numericals to solve ….. but most students will like to blow their time going and coming for tuition, travel time …. TV for hours and hours watching cricket / Tennis games, playing computer games …. My free lectures are not going to make much difference in spending of unnecessary money for coaching ….. I know very well , how much people enjoy …. ! spending unnecessarily !!

–

Do you know that there are NO poor / needy students in Bangalore.
–

Sometime back I had tried to teach for IIT JEE FREE. Discussed with a few NGOs and social service guys. Arranged rooms but got only 1 student. We had informed many people in many ways to inform students …. We did not get students who are ready to learn for free. So I am sure these lectures are NOT FREE. If anyone learns from these, s/he changes and that’s the gain / benefit. This change ( due to learning ) is very costly …. Most do not want to learn ………..

search for videos in http://www.skmclasses.kinja.com
You will get most videos. I say most because I do not upload all videos that I make. I have many more videos which are not in the net.

🙂

4 ) How can I get all your lectures ?

Ans : – Apart from my lectures there are approx 700 GB of PCM ( Phy, Chem, Math ) lectures. It takes approx 3 years of continuous download from scattered sources. I have ( 20,000 )Thousands of these. You can take ALL of them from me in an external 1 TB hard disk, instead of spending so much money and time again for downloading. These cover ( by Various Professors ) everything of Chemistry, Physics, Maths… Lot of this is from outside India … as foreigners have much wider heart than Indians ( as most of GNU / open source software have been developed by Non-Indians ). I observed the gaps in these videos, and thus I am solving IIT, APhO, Roorkey, IPhO Numericals. Videos made by me along with these videos gives a complete preparation.

Send me a mail at mokshya@gmail.com to contact me.

search for videos in http://www.skmclasses.kinja.com
You will get most videos. I say most because I do not upload all videos that I make. I have many more videos which are not in the net.

🙂

5 ) How do you get benefited out of this ?

Ans :- If anyone learns we all will have better people in this world. I will have better “ YOU “.
🙂

6 ) Why do you call yourself a Zookeeper ?

Ans :- This is very nicely explained at https://zookeepersblog.wordpress.com/z00keeper-why-do-i-call-myself-a-zoookeeper/

🙂

7 ) Where do you stay ?

Ans :- Presently I am in Bangalore.

🙂

8 ) If I need videos in a few topics can you make them for me ?

Ans :- We actively answers doubts at doubtpoint.
see http://skmclasses.weebly.com/doubtpoint.html
In case you appreciate our time and efforts involved in answering complicated Questions, then get Quality answers at doubtpoint.

🙂

9 ) Why did you write an article saying there are No Poor students ?

Ans :- There are lots of NGOs and others working for rural / poor children education at lower classes. While very less effort is on for std 9 till 12. Also see the answer in question number ( 3 ) above. In more than 2 decades of teaching I never met a Poor child who was seriously interested in ( higher ) studies. As I have a mind / thinking of a ” Physicist “, I go by ” Experimental Observation “.

It is not about what is being said about poor in media / TV etc, or ” what it should be ” ( ? ) …. It is about what I see happening. Also to add ( confuse ? you more )…. You must be knowing that in several states over many years now girl students have better ( by marks as well as by pass percentage ) result in std 10 / Board Exams….. well but NEVER a girl student came FIRST in IIT JEE … why ? [ The best rank by a Girl student is mostly in 2 digits, very rarely in single digit ] ????? So ????

🙂

10 ) How much do I have to study to make it to IIT ?

Ans :- My experience of Teaching for IIT JEE since 1989, tells me, Total 200 hours per subject ( PCM ) is sufficient. If you see my Maths and Physics videos, each subject is more than 200 hours. So if someone sees all the videos diligently, takes notes and remembers, …… Done.

🙂

11 ) What is EAMCET ?

Ans :- Engineering Agriculture and Medicine Common Entrance Test is conducted by JNT University Hyderabad on behalf of APSCHE. This examination is the gateway for entry into various professional courses offered in Government/Private Colleges in Andhra Pradesh.

12 ) In your videos are you covering other Exams apart from IIT ?

Ans : – Yes. See many videos made by solving problems of MPPET, Rajasthan / J&K CET, UPSEAT ( UPES Engineering Aptitude Test ), MHCET, BCECE ( Bihar Combined Entrance Competitive Examination Board ), WB JEE etc

🙂

13 ) What is SCRA ?

Ans : – Special Class Railway Apprentice (SCRA) exam is conducted by Union Public Service Commission (UPSC) board, for about 10 seats.That translates into an astonishing ratio of 1 selection per 10,000 applicants. The SCRA scheme was started in 1927 by the British, to select a handful of most intelligent Indians to assist them in their Railway Operations, after training at their Railway’s largest workshop, i.e. Jamalpur Workshop, and for one year in United Kingdom. The selected candidates were required to appear in the Mechanical Engineering Degree Examination held by Engineering Council (London).

Thanks for your time. To become my friend in google+ ( search me as mokshya@gmail.com and send friend request )

Read http://edge.org/responses/what-scientific-concept-would-improve-everybodys-cognitive-toolkit
🙂
The following video is a must see for full CO2 cycle, plates of Earth, Geological activities, stability of weather

🙂
Article in Nature says CO2 increase is good for the trees
http://thegwpf.org/science-news/6086-co2-is-greening-the-planet-savannahs-soon-to-be-covered-by-forests.html
🙂
http://climaterealists.com/index.php?id=9752

BBC documentary Crescent and Cross shows the 1000 years of fight between Christians and Muslims. Millions have been killed in the name of Religion. To decided whose GOD is better, and which GOD to follow. The fight continues.
–

Summary of Women

🙂
The Virus of Faith

🙂
The God delusion

🙂
cassiopeia facts about evolution

–

Intermediate Fossil records shown and explained nicely Fossils, Genes, and Embryos http://www.youtube.com/watch?v=fdpMrE7BdHQ

The Rise Of Narcissism In Women

🙂
13 type of women whom you should never court
http://timesofindia.indiatimes.com/life-style/relationships/man-woman/13-Women-you-should-never-court/articleshow/14637014.cms

🙂
Media teaching Misandry in India

http://www.youtube.com/watch?v=-M2txSbOPIo

Summary of problems with women
http://problemwithwomentoday.blogspot.in/2009/12/problem-with-women-today-what-in-hell.html

🙂
Eyeopener men ? women only exists
http://www.youtube.com/watch?v=6ZAuqkqxk9A

🙂
Each of you is an Activist in some way or other. You are trying to propagate those thoughts, ideas that you feel concerned / excited about.
–

Did you analyze your effectiveness ?

Culturomics can help you

😀
see how biased women are. Experimental proof. Women are happy when they see another woman is beating a man ( see how women misbehave with men )

🙂
http://www.youtube.com/watch?v=LlFAd4YdQks

–

see detailed statistics at

An eye opener in Misandry

My sincere advice would be to be EXTREMELY careful ( and preferably away ) of girls. As girls age; statistically certain behavior in them has been observed. Most Male can NOT manage those behaviors… Domestic violence, divorce etc are rising very fast. Almost in all cases boys / males are HUGE loosers. Be extremely choosy ( and think from several angles ) before even talking to a girl.
🙂
https://zookeepersblog.wordpress.com/save-the-male/

🙂

How women manipulate men
http://www.angryharry.com/esWomenManipulateMen.htm

Gender Biased Laws in India
https://zookeepersblog.wordpress.com/biased-laws/

🙂

Violence against Men

🙂

Only men are victimised

Men are BETTER than women
http://www.menarebetterthanwomen.com/
🙂

see

🙂

Male Psychology

Women are more violent than men
http://www.independent.co.uk/news/uk/home-news/women-are-more-violent-says-study-622388.html

🙂

In the year 2010, 168 men ended their lives everyday ( on average ). More husbands committed suicide than wives.
🙂

http://www.rediff.com/news/report/ncrb-stats-show-more-married-men-committing-suicide/20111028.htm

It is EXTREMELY unfortunate that media projects men as fools, women as superiors, Husbands as servants, and replaceable morons. In ad after ad worldwide from so many companies, similar msg to disintegrate the world is being bombarded. It is highly unacceptable misandry

🙂

It is NOT at all funny that media shows violence against MEN. Some advertisers are trying to create a new ” Socially acceptable culture ” of slapping Men ( by modern city women ). We ( all men ) take objection to these advertisements.
We oppose this Misandry bad culture. Please share to increase awareness against Men bashing

🙂

Think what are you doing … why are you doing ?

Every Man must know this …

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Manginas, White Knights, & Other Chivalrous Dogs

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bonded elements fixed ratio, usually chemical formula concentration amount solute mol IITJEE SKMClasses.weebly.com 1 dm 3 1000 cm solution coordinate bond shared pair electrons provided one bonding atoms called dative covalent bond covalent bond bond formed shared pair electrons cracking breaking long chained saturated hydrocarbonsIITJEE SKMClasses.weebly.com mixture shorter chained alkanesalkenes curly arrow symbol IITJEE SKMClasses.weebly.com reaction mechanisms IITJEE SKMClasses.weebly.com show movement electron Coaching ICWA Coaching CFA Coaching CFP Coaching CMAT Coaching School Tuitions CBSE School Tuitions Home Tuitions 9th STD Tuitions PUC Coaching 10th Std Tuitions College Tuitions Maths Tuitions Engineering Tuitions Accounts & Finance Tuitions MBA & BBA Coaching Microbiology & Biotech Tuitions Study Abroad GRE & SAT Coaching GMAT Coaching IELTS/TOEFL Coaching PTE Coaching proteins protonation pyridines pyrroles quinones quinolines radical reaction radicals rearrangement receptors reduction regioselectivity retro reaction rhodium ring closure ring contraction ring expansion ring opening ruthenium samarium scandium Schiff bases selenium self-assembly silicon sodium solid-phase synthesis solvent effects spectroscopy sphingolipids spiro compounds stereoselective synthesis stereoselectivity steric hindrance steroids Stille reaction substituent effects sulfates sulfonamides sulfones sulfoxides sulfur supported catalysis supramolecular tandem reaction tautomerism terpenoids thioacetals thiols tin titanium total synthesis transesterification transition metals transition states tungsten Umpolung vinylidene complexes vitamins Wacker reaction Wittig reaction ylides zeolites zinc BRST Quantization Effective field theories Field Theories Higher Dimensions Field Theories Lower Dimensions Large Extra Dimensions Lattice Quantum Field Theory Nonperturbative Effects Renormalization Group Renormalization Regularization skmclasses.weebly.com Renormalons Sigma Models Solitons Monopoles skmclasses.weebly.com Instantons Supersymmetric gauge theory Topological Field Theories 1/N Expansion Anyons Chern-Simons Theories Confinement Duality Gauge Field Theories Lattice Gauge Field Theories Scattering Amplitudes Spontaneous Symmetry Breaking Strong Coupling Expansion Topological States Matter Wilson ‘t Hooft skmclasses.weebly.comPolyakov loops Anomalies Field skmclasses.weebly.comString Theories BRST Symmetry Conformal skmclasses.weebly.com W Symmetry Discrete skmclasses.weebly.comFinite Symmetries Gauge Symmetry Global Symmetries Higher Spin Symmetry Space-Time Symmetries AdS-CFT Correspondence Black Holes String Theory Bosonic Strings Brane Dynamics Gauge Theories Conformal Field Models String Theory D-branes dS vacua string theory F-Theory Flux compactifications Gauge-gravity correspondence Holography skmclasses.weebly.comcondensed matter physics (AdS CMT) Holography skmclasses.weebly.comquark-gluon plasmas Intersecting branes models Long strings 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skmclasses.weebly.com String Models CP violation Electromagnetic Processes skmclasses.weebly.com Properties GUT Heavy Quark Higgs Kaon LEP HERA skmclasses.weebly.com SLC Neutrino Physics Quark Masses skmclasses.weebly.comSM Parameters Rare Decays Standard Model Supersymmetric Standard Model Technicolor skmclasses.weebly.com Composite Models Chiral Lagrangians Deep Inelastic Scattering Higher Twist Effects Lattice QCD Parton Model Phase Diagram QCD Phenomenological Models QCD Quark-Gluon Plasma Resummation Sum Rules Aim Global Education Koramangala Computer Networking Training Cloud Computing Training JBOSS Training Juniper Certification Training L2 & L3 Protocol Training MCTS Training Engineering design Training CAD & CAM Training MATLAB Training PLC Training SCADA Training VLSI Design Multimedia & Design Training 2D Animation Training 3D Animation Training 4D Animation Training CorelDRAW Training VFX Training Web Technologies Training ASP.Net Training JQuery pair breaking formation 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delocalised electrons, bonded together strong metallic bonds greenhouse effect process IITJEE SKMClasses.weebly.com absorption subsequent emission infrared radiation atmospheric gases warms lower atmosphere planet’s surface group vertical column Periodic Table Elements group IITJEE SKMClasses.weebly.com similar chemical properties skmclasses.weebly.com atoms skmclasses.weebly.comnumber outer shell electrons Hess law reaction IITJEE SKMClasses.weebly.com one route skmclasses.weebly.com initial final conditions IITJEE SKMClasses.weebly.com skmclasses.weebly.com total enthalpy change skmclasses.weebly.com skmclasses.weebly.com route heterogeneous catalysis reaction IITJEE SKMClasses.weebly.com catalyst IITJEE skmclasses.weebly.com different physical state reactants; frequently, reactants IITJEE SKMClasses.weebly.com gases whilst catalyst solid heterolytic fission breaking covalent bond IITJEE SKMClasses.weebly.com both bonded electrons going IITJEE SKMClasses.weebly.com one atoms, forming cation (+ ion) skmclasses.weebly.com IITJEE SKMClasses.weebly.com anion ion homogeneous catalysis reaction catalyst skmclasses.weebly.com reactants physical state, IITJEE SKMClasses.weebly.com frequently aqueous gaseous state homologous series series organic compounds IITJEE SKMClasses.weebly.com skmclasses.weebly.com functional group, IITJEE SKMClasses.weebly.com successive member differing homolytic fission breaking covalent bond IITJEE SKMClasses.weebly.com one bonded electrons going IITJEE SKMClasses.weebly.com atom, forming two radicals hydrated Crystalline skmclasses.weebly.com containing water molecules hydrocarbon compound hydrogen skmclasses.weebly.com carbon hydrogen bond strong dipole attraction IITJEE SKMClasses.weebly.com electron deficient hydrogen atom (O H on different molecule hydrolysis reaction IITJEE SKMClasses.weebly.com water aqueous hydroxide ions IITJEE SKMClasses.weebly.com breaks chemical compound skmclasses two compounds initiation first step radical 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SKMClasses.weebly.com molar volume IITJEE SKMClasses.weebly.com mole gas. units molar volume IITJEE SKMClasses.weebly.com dm room temperature skmclasses.weebly.com pressure molar volume approximately 24.0 substance containing IITJEE skmclasses.weebly.com many particles thereIITJEE SKMClasses.weebly.com carbon atoms exactly 12 g carbon isotope molecular formula number atoms IITJEE SKMClasses.weebly.com element molecule molecular ion M positive ion formed mass spectrometry IITJEE SKMClasses.weebly.com molecule loses electron molecule small group atoms held together covalent bonds monomer small molecule IITJEE SKMClasses.weebly.com combines IITJEE SKMClasses.weebly.com monomers polymer nomenclature system naming compounds nucleophile atom group atoms attracted electron deficient centre atom donates pair electrons covalent bond nucleophilic substitution type substitution reaction IITJEE SKMClasses.weebly.com nucleophile attracted electron deficient centre atom, IITJEE SKMClasses.weebly.com donates pair electrons IITJEE SKMClasses.weebly.com new covalent bond oxidation Loss electrons IITJEE SKMClasses.weebly.com increase oxidation number oxidation number measure number electrons IITJEE SKMClasses.weebly.com IITJEE SKMClasses.weebly.com atom uses bond IITJEE SKMClasses.weebly.com atoms another element. Oxidation numbers IITJEE SKMClasses.weebly.com derive d rules oxidising agent reagent IITJEE SKMClasses.weebly.com oxidises (takes electrons from) another species percentage yield period horizontal row elements Periodic Table Elements show trends properties across period periodicity regular periodic variation properties elements IITJEE SKMClasses.weebly.com atomic number position Periodic Table permanent dipole small charge difference across bond resulting IITJEE SKMClasses.weebly.com difference electronegativities bonded atoms permanent dipole dipole force attractive force IITJEE SKMClasses.weebly.com permanent dipoles neighbouring polar molecules pi bond (p bond reactive part double bond formed above skmclasses.weebly.com below plane bonded atoms sideways overlap p orbitalspolar covalent bond bond IITJEE SKMClasses.weebly.com permanent dipole polar molecule molecule IITJEE SKMClasses.weebly.com IITJEE SKMClasses.weebly.com overall dipole skmclasses account dipoles across bonds polymer long molecular chain built monomer units precipitation reaction formation solid solution during chemical reaction Precipitates IITJEE SKMClasses.weebly.com formed IITJEE SKMClasses.weebly.com two aqueous solutions IITJEE SKMClasses.weebly.com mixed together principal quantum number n number representing relative overall energy orbital IITJEE SKMClasses.weebly.com increases distance nucleus sets orbitals IITJEE SKMClasses.weebly.com value IITJEE skmclasses.weebly.com electron shells energy levels propagation two repeated radical substitution IITJEE SKMClasses.weebly.com build up products chain reaction radical species unpaired electron rate reaction change concentration reactant product redox reaction reaction IITJEE SKMClasses.weebly.com reduction skmclasses.weebly.com oxidation take IITJEE SKMClasses.weebly.com reducing agent reagent IITJEE SKMClasses.weebly.com reduces (adds electron to) species reduction Gain electrons decrease oxidation number yield actual amount mol product theoretical amount mol product Chemistry reflux continual boiling skmclasses.weebly.com condensing reaction mixture ensure IITJEE SKMClasses.weebly.com reaction IITJEE SKMClasses.weebly.com without contents flask boiling dry relative atomic mass weighted mean mass atom element compared one twelfth mass IITJEE SKMClasses.weebly.com atom carbon relative formula mass weighted mean mass formula unit compared IITJEE SKMClasses.weebly.com one twelfth mass atom carbon relative isotopic mass mass atom isotope compared IITJEE SKMClasses.weebly.com one twelfth mass atom carbon relative molecular mass weighted mean mass molecule compared twelfth mass atom carbon 12 repeat unit specific arrangement atom s IITJEE SKMClasses.weebly.com occurs structure over over again. Repeat units IITJEE SKMClasses.weebly.com included brackets outside IITJEE SKMClasses.weebly.com symbol n Salt chemical compound formed IITJEE SKMClasses.weebly.com IITJEE SKMClasses.weebly.com acid IITJEE SKMClasses.weebly.com H+ ion acid IITJEE skmclasses.weebly.com been replaced metal ion another positive ion such IITJEE skmclasses.weebly.com ammonium ion, NH saturated hydrocarbon IITJEE SKMClasses.weebly.com single bonds only shell group atomic orbitals IITJEE SKMClasses.weebly.com skmclasses.weebly.com principal quantum number known main energy level simple molecular lattice three dimensional structure molecules, bonded together weak intermolecular forces skeletal formula simplified organic formula, IITJEE SKMClasses.weebly.com hydrogen atoms removed alkyl chains, leaving carbon skeleton skmclasses.weebly.com associated functional groups species particle IITJEE SKMClasses.weebly.com part chemical reaction specific heat capacity, c energy IITJEE SKMClasses.weebly.com raise temperature 1 g substance 1 C spectator ions Ions present part chemical reaction standard conditions pressure 100 kPa 1 atmosphere stated temperature usually 298 K (25 °C), skmclasses.weebly.com concentration 1 mol dm reactions aqueous solutions standard enthalpies enthalpystandard solution solution known concentration Standard solutions normally IITJEE SKMClasses.weebly.com titrations IITJEE SKMClasses.weebly.com determine unknown information another substance Chemistry standard state physical state substance under standard conditions 100 kPa 1 atmosphere) skmclasses.weebly.com 298 K 25 C stereoisomers Compounds skmclasses.weebly.com structural formula IITJEE SKMClasses.weebly.com different arrangement atoms space stoichiometry molar relationship IITJEE SKMClasses.weebly.com relative quantities substances part reaction stratosphere second layer Earth’s atmosphere, containing ‘ozone layer’, about 10 km IITJEE SKMClasses.weebly.com 50 km above Earth’s surface structural formula formula showing minimal detail skmclasses.weebly.com arrangement atoms molecule structural isomers Molecules IITJEE SKMClasses.weebly.com skmclasses.weebly.com molecular formula different structural arrangements atoms subshell group skmclasses.weebly.com type atomic orbitals s, p, d f within shell substitution reaction reaction IITJEE SKMClasses.weebly.com atom group atoms replaced different atom group atoms termination step end radical substitution IITJEE SKMClasses.weebly.com two radicals combine IITJEE SKMClasses.weebly.com molecule thermal decomposition breaking chemical substance IITJEE SKMClasses.weebly.com heat skmclasses least two chemical substances troposphere lowest layer Earth’s atmosphere extending Earth’s surface about 7 km (above poles) about 20 km above tropics unsaturated hydrocarbon hydrocarbon containing carbon carbon multiple bonds van der Waals’ forces Very weak attractive forces IITJEE SKMClasses.weebly.com induced dipoles neighbouring molecules volatility ease IITJEE 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Later Sri Kumaran Children’s Home Survey No 44 – 50, Mallasandra Village Uttarahalli Hobli, Off Kanakapura Main Road, Bangalore skmclasseslocality namedIITJEE SKMClasses.weebly.com current DD kendra is situated known IITJEE skmclasses.weebly.com JC Nagar or Jayachamarajendra Nagar Delhi Public School, North Campus Survey No. 35/A, Sathanur Village Jala Hobli, Bangalore Jayanagar IITJEE SKMClasses.weebly.com literally Victory City Jayanagar IITJEE skmclasses.weebly.com traditionally regarded IITJEE skmclasses.weebly.com southern end Bangalore South End Circle “, wherein six roadsIITJEE SKMClasses.weebly.com different areas meet skmclasses.weebly.com historic Ashoka Pillar mark southern end city bear this fact. newer extensions IITJEE SKMClasses.weebly.com taken away this distinctionIITJEE SKMClasses.weebly.com Jayanagar still remains one IITJEE SKMClasses.weebly.com southern parts city Malleshwaram Basavanagudi Malleshwaram north Bangalore, Basavanagudi south IITJEE SKMClasses.weebly.com areas oldest Bangalore skmclasses.weebly.com residents IITJEE SKMClasses.weebly.com original inhabitants City. Malleswaram PSBB Learning Leadership Academy
# 52, Sahasra Deepika Road, Laxmipura Village, Off Bannerghatta Main Road Bangalore located actually north-west Bangalore derives IITJEE SKMClasses.weebly.com name IITJEE SKMClasses.weebly.com famous Kaadu Malleshwara temple 8th Cross in Malleshwaram, skmclasses.weebly.comGandhibazar/ DVG Road in Basavanagudi IITJEE SKMClasses.weebly.com popular areas in Bangalore skmclasses.weebly.comshopping during festival times. Malleswaram been homeIITJEE SKMClasses.weebly.com several important personalities skmclasses.weebly.cominstitutions. Bangalore’s own Nobel laureate, C.V. Raman, late Veena Doreswamy Iyengar skmclasses.weebly.com M.Chinnaswamy cricket stadium is named, academician M.P.L. Sastry, poet G.P. Rajaratnam skmclasses.weebly.com Dewan Seshadri Iyer institutions IITJEE SKMClasses.weebly.com Canara Union club Konkani-speaking people in 1930 IITJEE SKMClasses.weebly.comIITJEE SKMClasses.weebly.com this day hosts a variety cultural activities Malleswaram Association, hub area’s sporting activity since 1929 skmclasses.weebly.com Chowdaiah Memorial hosting great names music skmclasses.weebly.comtheatre. AccordingIITJEE SKMClasses.weebly.com recent figures available IITJEE SKMClasses.weebly.com Bangalore Development Authority BDA Malleswaram’s net population density is 521 personsIITJEE SKMClasses.weebly.com hectare, Bangalore City Corporation standard is 352IITJEE SKMClasses.weebly.com hectare Sadhashivnagar Sadashivanagar arguably IITJEE SKMClasses.weebly.com elite skmclasses.weebly.comexpensive neighborhood in Bangalore India fashionable among politicians, movie starsIITJEE SKMClasses.weebly.com millionaires afford homes “Beverly Hills Bangalore,” having IITJEE SKMClasses.weebly.com address in Sadashivanagar connotes high level prestige success fame Vijayanagar derivesIITJEE SKMClasses.weebly.com nameIITJEE SKMClasses.weebly.com Vijayanagara empire IITJEE SKMClasses.weebly.com flourished in south India during 15th skmclasses.weebly.com16th centuries.Vijayanag ar East is popularly known IITJEE base skmclasses.weebly.com RPC Layout (Railway Parallel Colony Layout), since this layout is along railway track. IITJEE skmclasses.weebly.com recently renamed Hampi Nagar Hampi capital Vijayanagar Empire Vijayanagar houses a large Public Library, IITJEE SKMClasses.weebly.com is one largest in Karnataka Halasuru Halasuru formerly known IITJEE skmclasses.weebly.com Ulsoor oldest neighbourhoods Indian city Bangalore predominant Tamil speaking population renowned skmclasses.weebly.com numerous temples skmclasses.weebly.comrather narrow streets skmclassesprominant areas CityIITJEE SKMClasses.weebly.com Sanjay Nagar skmclasses.weebly.com RT Nagar, Hebbal, Vyalikaval, Yeshwanthpur, Sriramapura, Rajajinagar, Rajarajeshwarinagar, Chickpet, Chamarajpet, V V Puram, Mavalli, Hanumanthanagar, Padmanabhanagar Hosakerehalli Sarakki, BTM Layout, Domlur, Gandhinagar, Vasanthanagar, Vivek Nagar, Cox Town, Frazer Town Benson Town Bangalore Roads Many roads Bangalore had European names South Parade Road, Albert Victor Road, Hardinge Road, Grant Road several roads Bangalore derived Delhi Public School Sarjapur, Bangalore East Survey No.43/1B & 45, Sulikunte Village, Dommasandra Post, Bangalore IITJEE SKMClasses.weebly.com military nomenclature Mahatma Gandhi Road MG Raod called IITJEE skmclasses.weebly.com South Parade Roadskmclasses.weebly.com nomenclature Independence Edify School Electronic City
105, 34th Main, 23rd Cross, Sector-A, Surya Nagar Phase-2, Anekal-Chandapura Main Road, Electronic City Chamarajpet First Main Road named Albert Victor Road 1889 future King Edward VII Englskmclasses.weebly.com renamed Alur Venkatarao Road,IITJEE SKMClasses.weebly.com well-known Kannada writer skmclasses.weebly.comprotagonist unification National Public School, Koramangala National Games Village Koramangala, Bangalore Kannada-speaking areas andlater shortened IITJEE skmclasses.weebly.com A.V. Road. Avenue road earlier known Doddapete Infantry Road became Bhagavan Mahaveer Road 2004 Chamarajendra Park Jyothi Kendriya Vidyalaya Yelachenahalli, Kanakapura Road Bangalore IITJEE skmclasses.weebly.com Cubbon Park IITJEE SKMClasses.weebly.com Sir Mark Cubbon British Commissioner Mysore mid-19th century. Fraser Town, IITJEE SKMClasses.weebly.com named Sir Stuart Fraser scholar tutor Maharaja Krishnaraja Wadiyar IV Pulakeshinagar. Hardinge Road old name Pampa Mahakavi Road. sometime, Cunningham Road crowded bazaar being called Sampangi Ramaswamy Temple Road Race Course Road became Devraj Urs Road National Public School, Rajajinagar 1036-A, Purandarapura, V Block, Rajajinagar, Bangalore skmclasses.weebly.comGrant Road became Vittal Mallya Road IITJEE SKMClasses.weebly.com two Vittal Mallya Roads skmclasses bund Sampangi Tank Kanteerava Stadium Gear Innovative International School GEAR Road, Doddakannelli, Off Sarjapur Road & Outer Ring Road, Bangalore IITJEE SKMClasses.weebly.com built MacIver Town Shantala Nagar Assayee Road Meanee Road those names commemoration wars fought Madras New Horizon Gurukul Ring Road Marathalli, Behind New Horizon College of Engineering, Bangalore , Bangalore IITJEE skmclasses.weebly.com Sappers, BGS National Public School Ramalingeshwara Cave Temple Hulimavu, Bangalore IITJEE SKMClasses.weebly.com Presidency School (Bangalore – East) CA Site 7P1A, 2nd A Main, 3rd A cross, East of NGEF Layout, Kasturinagar, Bangalore British Army against Marathas first decade 19th century Basavanagudi, meaning temple Basava skmclasses.weebly.com big bull situated area reason behind naming area Basavanagudi extension skmclassesformed around 1900. Gandhi Bazar, earlier known merely Angadi Beedhi School Of India Anekal Road, Bannerghatta, Bangalore skmclasses formed Kumarapark came skmclasses existence 1947, year Indian Independence, whereas Jayanagar skmclasses.weebly.comRajajinagarIITJEE SKMClasses.weebly.com thought year later 1948 skmclasses.weebly.com orchards Bangalore Palace skmclasses developed housing colony skmclasses.weebly.comnamed Sadashivanagar 1960,IITJEE SKMClasses.weebly.com Orchids The International School Jalahalli, Nagarbavi, Mysore Road, Sarjapur Road, BTM, Bangalore well-known freedom fighter Dakshina Kannada Karnad Sadashiva Rao BVK Iyengar Road Byappana Halli Byatarayanapura Byrasandra C.V Raman Nagar Cambridge Layout Cambridge Road Cantonment Carmelaram Castle Street Central Street Chamarajapet Shanthi Theatre South End Circle INOX Shree Garuda Swagath Mall, 4th Floor, Tilak Nagar Main Road INOX Bangalore Central-2, 5th Floor, 45th Cross Maheshwari Theater Bannerghatta Main Road Gopalan Cinemas Gopalan Innovation Mall, JP Nagar 3rd Phase Chandapura Chandra Layout Global Academy For Learning Sri Chowdeshwari Farm, Near Global Village IT Park, National Public School, HSR Layout P2/32, Sector 4, HSR Layout Bangalore Pattanagere Main Road, Rajarajeshwarinagar, Bangalore Chickpet Chikkabanavara Chikkadugodi Chikkallasandra Chikkamavalli Cholara Palya Chowdeshwari Temple Street Chunchagatta Church Street Clevelskmclasses.weebly.com Town CMH Road Coles Park Commercial Street Commissariat Road Cooke Town Corporation Circle Cottonpet Cox Town Crescent Road Cubbon Park Cubbon Road Cubbonpet Cunningham Road Dairy Circle Dasara Halli Dasarahalli Devaiah Park Devana Halli Devanahalli Devara Chikkana Halli Devara Jeevana Halli Devasandra Dharmaram College Dickenson Road Dispensary Road Dodda Banaswadi Dodda Bommasandra Dodda Kallasandra Dodda Kanna Hally Dodda Mavalli Doddaballapur Road Doddaballapura Doddana Kundi Dollars Colony Domlur Domlur 2nd Stage Domlur Ring Road Dooravani Nagar Dr. Ambedkar Veedhi Dr. DVG Road Delhi Public School, South 11 K.M., kanakapura Road Konanakunte Post, Bangalore Dr. Raj Kumar Road Dr. TCM Royan Road Ejipura Electronic City Field Marshal Cariappa Road Frazer Town Ganapathi Nagar Gandhi Bazaar Gandhi Nagar Ganga Nagar Gangadhar Chetty Road Ganigarpet Garvebhavi Palya Gavipuram Extension Gayathri Nagar Geddala Halli Geddalahalli Giri Nagar Giri Nagar 1st Phase Giri Nagar 2nd Phase GM Palya Gokula Golf Course Road Gorgunte Palya Govindaraj Nagar Green Park Extension, Guddada Halli Gundopanth Street National Public School, Indiranagar 12 A Main HAL II Stage, Bangalore H.Siddaiah Road Haines Road HAL HAL 2nd Stage HAL 3rd Stage HAL Airport Road Hampi Nagar Hanumantha Nagar Hayes Road HBR Layout Hebbal Kempapura Hebbal Ring Road Hegde Nagar Heggana Halli Hennur Hesaraghatta HKP Road HMT Layout Hongasandra Hoody Horamavu Hosakere Halli photochemistry photooxidation piperidines polyanions polycations polycycles polymers Porphyrins prostaglandins protecting groups Entrance Coaching IIT Entrance Coaching CLAT Entrance Coaching AICEE Coaching TANCET Entrance Coaching PMT Entrance Coaching Language Classes Spoken English Classes Spoken Hindi Classes Foreign Languages Coaching Spoken Kannada Classes Spoken Gujarati Classes Competitive Exams Coaching KMAT Coaching Online CAT Coaching GATE Coaching IBPS Coaching RRB Coaching Civil Services Coaching UGC Net Coaching SSB & NDA Coaching UPSC Coaching IAS Coaching TNPSC Coaching Accounts & Finance CA Training PHP & MySQL Training Spring Training Web Designing Training Administration Training VMWare Training ITIL Training SharePoint Training SAN Training Linux Administration Training Database Training Data Warehousing Training Database Testing Training HADOOP Training Oracle DBA Training SQL Server Training Programming Languages Java & J2EE Training C C++ Training Perl Programming Training Python Programming Training Shell Scripting Training Mobile Development Training Android Development Training iPhone Development Training Mobile Application Testing Training Mobile Gaming Training Mobile Application Development Training Oakridge International School Oakridge International School, Sarjapur Road, , Bangalore School of India, Bannerghatta, Bangalore Delhi Public School DPS North Campus, Yelahanka, Bangalore Jain International Residential School (JIRS), Jakkasandra Post, Bangalore Delhi Public School (DPS East), Sarjapur, Bangalore TREAMIS World School, Electronics City, Bangalore South Delhi Public School (South), Kanakapura Road, Bangalore The Deen’s Academy, Whitefield, Bangalore National Public School (NPS), Koramangala, Bangalore Royale Concorde International School, Kalyan Nagar, Bangalore Freedom International School, HSR Layout, Bangalore Air Force School Army Public School Bangalore Military School BGS International School Cambridge Public School Delhi Public School Deva Matha Central School Jain International Residential School Kendriya Vidyalaya A M C School A.S.C Public School Amara Jyothi Public School Anand Shiksha Kendra ICSE Syllabus ACTS Secondary School B Mona High School Baldwin Boys High School Baldwin Girls High School Bishop Cotton Boys School Bishop Cotton Girls School Brigade School Candor International School Cambridge Public School Cathedral High School Chinmaya Vidyalay Christ Academy Ekya School Gnan Srishti School of Excellence Gopalan National School India International School IIS Lawrence School-ICSE New Horizon Public School Notre Dame Academy Paradise Residential School Patel Public School Podar International School Prakriya Green Wisdom School Primus School Ryan International School Sishu Griha St. Francis De Sales (SFS) High School Sherwood High Sri Kumaran Childrens Home St Francis School St Johns High School St Thomas Public School St. Patricks Academy St. Peters School Vibgyor High CBSE Syllabus AECS Magnolia Maaruti Public School Amaatra Academy Amrita Vidyalayam BGS-NPS School Brigade School BRS Global Centre for Excellence Capitol Public School CMR National Public School Delhi Public School East, South, North Edify School EuroSchool Freedom International School Geethanjali Montessori Geethanjali Vidhyalaya Gitanjali International School GISB Greengrove International School Gomathy Global School Harvest International School JSS Public School Kendriya Vidyalaya KV Manipal Tattva School Mirambika School for New Age NITTE International School National Centre for Excellence NCFE National Public School New Horizon Gurukul NHG Oakridge International School Presidency School PSBB LLA Padma Seshadri Bal Bhavan Radcliffe School Ravindra Bharathi Global School Sadhguru Sainath International School SSI Sri Kumaran Childrens Home Sunrise International Residential School Sujaya School The Samhita Academy Vagdevi Vilas School Venkat International Public School VIPS Vyasa International School Zee School IGCSE Syllabus Asia Pacific World School Krupanidhi Cambridge International School Candor International 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Primary Years Programme Colegio Anglo Mexicano MEXICO Milgate Primary School, AUSTRALIA Diploma Programme Australian International School Indonesia Pejaten Campus INDONESIA Instituto Educativa Fiscomisional Celina Vivar Espinosa, ECUADOR Unidad Educativa Juan de Salinas, ECUADOR Primary Years Programme Academia Moderna Charter, UNITED STATES Beacon School BRAZIL Dr. Orlando Edreira Academy, School 26, UNITED STATES Westhill Institute Carpatos Elementary Campus, MEXICO Westhill Institute, S.C. 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Colin English Elementary UNITED STATES Jose de Escandon Elementary, UNITED STATES Lincoln Elementary School, UNITED STATES Qingdao Amerasia International School CHINA Roland Park K-8 Magnet School for International Studies, UNITED STATES Theodore Roosevelt Elementary School, UNITED STATES Woodrow Wilson Elementary UNITED STATES Middle Years Programme Cache La Poudre Middle School, UNITED STATES Carl Hankey K-8 School, UNITED STATES Cedar Shoals High School UNITED STATES Concord High School, UNITED STATES Harry Stone Montessori Academy, UNITED STATES International School of Monterey, UNITED STATES Johnnie R. Carr Middle School, UNITED STATES Prairie Seeds Academy, UNITED STATES Roland Park K-8 Magnet School, UNITED STATES Sterling Middle School UNITED STATES The Aga Khan Academy, Hyderabad, INDIA Diploma Programme Ausangate Bilingual School PERU Author’s School Istochnik RUSSIAN FEDERATION Colegio Fiscal Técnico El Chaco ECUADOR Colegio Juan Bautista Montini ECUADOR Colegio Nacional Ciudad de Cuenca ECUADOR Colegio Nacional Experimental Salcedo, ECUADOR Colegio Nacional Machachi, ECUADOR Colegio Nacional Mixto El Playon, ECUADOR Colegio Técnico Cascales, ECUADOR Dar al Marefa Private School, UNITED ARAB EMIRATES Escola Internacional del Camp SPAIN Gymnasium Jovan Jovanovic Zmaj SERBIA ISTEK Private Acibadem Schools TURKEY Instituto Superior Tecnológico Carlos Cisneros ECUADOR Instituto Superior Tecnológico Daniel Alvarez Burneo ECUADOR Instituto Técnico Superior Isabel de Godin ECUADOR King Abdulaziz Saudi School Rome ITALY Riga State Gymnasium Nr. 2 LATVIA Saudi School Vienna AUSTRIA State IS Seeheim Jugenheim/Schuldorf Bergstrasse GERMANY Unidad Educativa Bolívar, ECUADOR Unidad Educativa Abelardo Moncayo, ECUADOR Unidad Educativa Fiscomisional Verbo Divino, ECUADOR Unidad Educativa Mayor ECUADOR Unidad Educativa Nueva Semilla, ECUADOR Unidad Educativa Temporal Juan Bautista Vásquez, ECUADOR Primary Years Programme Ajman Academy UNITED ARAB EMIRATES British International School Kiev UKRAINE Cache La Poudre Elementary School, UNITED STATES Dr. Thomas S. O Connell Elementary School UNITED STATES Gems World Academy Abu Dhabi UNITED ARAB EMIRATES Hebron-Harman Elementary School, UNITED STATES International School of Solothurn, SWITZERLAND Lisa-Junior Primary School AUSTRIA Madison Richard Simis Elementary School, UNITED STATES Miina Härma Gümnaasium, ESTONIA Riffenburgh Elementary School UNITED STATES Roscoe Wilson Elementary School, UNITED STATES Singapore International School INDIA William H. 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Atms. Educ. Institution Kogalym Secondary School ?8, RUSSIAN FEDERATION Phorms Bilingual Gymnasium, GERMANY Royal High School, UNITED STATES SIS Swiss International School Stuttgart-Fellbach, GERMANY Seedling Public School INDIA The British School of Beijing CHINA Unidad Educativa Fiscal Experimental del Milenio, ECUADOR Unidad Educativa Juan de Velasco ECUADOR Unidad Educativa Tumbaco, ECUADOR École secondaire Gaétan Gervais, CANADA École secondaire Hanmer CANADA Stonehill International School American School of Bombay Mumbai Day school offering PYP MYP DP Dhirubhai Ambani International School Mumbai Day school offering DP Ecole Mondiale World School, Mumbai Day school offering DP Jamnabai Narsee School Mumbai Day school offering DP Ahmedabad International School Ahmedabad Day School offering PYP Mahatma Gandhi International School Ahmedabad Day school offering MYP Mahindra United World College of India Pune Boarding school offering DP Mercedes-Benz International School Pune American Embassy School Delhi Day school offering DP The British School, Delhi Day school offering DP Pathways World School, Gurgaon Boarding school offering PYP DP SelaQui World School, Dehra Dun Boarding school offering DP Canadian International School, Bangalore Mixed Boarding Day school offering DP International School of Bangalore, Bangalore Mixed Boarding Day school offering DP Oakridge International School Hyderabad Day school offering PYP Chinmaya International Residential School Coimbatore Boarding school offering DP Good Shepherd International School Ooty Boarding school offering DP Kodaikanal International School, Kodaikanal Boarding school offering DP Home Tuition Group teachers available small groupsstudents IB International Baccalaureate Programme, IGCSE, ISc, ICSE, CBSE Schools offering IB ( International Baccalaureate ) Programme Bangalore International School Geddalahalli Hennur Bagalur Road Kothanur Post Bengaluru India 560 077 Stonehill International School, 1st Floor, Embassy Point #150, Infantry Road Bengaluru 560 001 Stonehill International School 259/333/334/335 Tarahunise Post Jala Hobli, Bengaluru North 562157 Candor International School Begur Koppa Road, Hullahalli Off Bannerghatta Road, Near Electronic City Bangalore 560105 Greenwood High International School Bengaluru, No.8-14, Chickkawadayarapura, Near Heggondahalli Gunjur Post, Varthur Sarjapur Road, Bangalore 560087 Sarla Birla Academy, Bannerghatta, Bangalore, Canadian International School, Yelahanka, Bangalore Indus International School Billapura Cross Sarjapur Bangalore

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