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Question-1

Classify the following hydrides into covalent, ionic and interstitial hydrides.

Solution:
NH3, ZrH2, CaH2, NaH, B2H6

Covalent = NH3 B2H6

Ionic = NaH, CaH2

Interstitial = ZrH2.

Question-2

How is H2O2 manufactured?

Solution:
Industrially H2O2 is prepared by the auto oxidation of 2 hydroxy anthraquinols. It involves a cycle of reactions. The net reaction is to catalyst union of H2 and O2 to yield H2O2

It is concentrated by careful distillation under low pressure.

Question-3

What is the use of Zeolite / per mutit?

Solution:
Zeolite or permutit is a sodium aluminium silicate. Na Al SiO4.3H2O. When hard water, which contains Ca2+ / Mg2+ ions, is passed through Zeolite / permutit, Na+ ion in the silicate gets exchanged for Ca+ / Mg2+ in hard water. Thus hard water is softened.

Question-4

What is meant by 100-volume of Hydrogen peroxide?

Solution:
Each milliliter of 100-volume H2O2 will liberate 100 volumes of oxygen at STP. It may be 30% solution H2O2.

Question-5

Give examples for electron deficient, electron-precise and electron rich molecular hydrides.

Solution:
Electron deficient: B2H6 (has less number of electrons to write Lewis structure)
Electron – precise: CH4
Electron – rich: NH3 and H2O (N and O have lone pairs of electrons).

Question-6

Why HF, H2O and NH3 have higher boiling points, and aggregation?

Solution:
Fluorine, oxygen and nitrogen are electronegative elements: They have lone pairs of electron in HF, H2O and NH3, electron rich hydride.

Question-7


Solution:
2KMnO4 + 3H2SO4 + 5H2O2 → K2SO4 + 2MnSO4 + 8H2O + 5O2

KMnO4 is converted into MnSO4: Oxidation number of Mn is changed from +7 to +2 by H2O2. That is H2O2 acts as a reducing agent, giving electrons to manganese. H2O2 is changed to O2 by KMnO4. Oxidation number of oxygen in H2O2 is changed from –1 to 0 in oxygen molecule. Hence KMNO4 removes electron from oxygen of H2O2 . Hence H2O2 is oxidized by KMNO4 to H2O.

2PbS(s) + H2O2 
 PbSO4(s) + 4H2O (l)

S2- in PbS is oxidized to SO4; oxidation number of S in Pbs (-2) changed to (+6) in PbSO4. Electrons are removed from Pbs by H2O2 to convert PbS to PbSO4. Hence H2O2 is an oxidizing agent.

H2O2 is converted into H2O : Oxidation number (-1) in H2O2 is changed into (-2) in H2O. Hence H2O2 is reduced by PbS.

Question-8

How is H2O2 concentrated?

Solution:
Aqueous H2O2 solutions spontaneously decompose to give H2O and O2. Hence 1% H2O2, formed during preparation cannot be concentrated by distillation under atmospheric pressure. Hence H2O2 solution is concentrated to 30% by distillation under reduced pressure. This further concentrated to 85% by careful distillation under low pressure. The remaining water is frozen out to give pure H2O2.

Question-9

What is nascent hydrogen? How is its reactivity?

Solution:
The hydrogen at the time of its production (new born) is much more reactive and is called nascent hydrogen. It is in a atomic state at the moment of its formation.

E.g. H2 molecule does not reduce KMnO4. But, Zn and HCl reduces KMnO4. Decolourise KMnO4 .

Zn + H2SO4
ZnSO4 + 2(H); – 2KMnO4 + 3H2SO4 + 10H K2SO4 + 2MnSO4 + 8H2O

Question-10

What is the reaction involved using H2O2 for renovating old painting?

Solution:
Old paintings rendered black PbS by the atmospheric H2S. Black PbS in painting is oxidized by H2O2 to white PbSO4

H2O2
 H2O + (O)

PbS + 4(O)  PbSO4





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