XII CHEM Practice assignments dated 26.06.12

p-block elements
1.
In the following cases rearrange the compounds as directed:

(i) In an increasing order of basic strength:

C6H5NH2,C6H5 N (CH3)2, (C2H5)2 NH and CH3NH2

(ii) In a decreasing order of basic strength:

Aniline, p-nitroaniline and p-toluidine

(iii) In an increasing order of pKb values:

C2H5NH2, C6H5 NHCH3, (C2H5)2 NH and C6H5NH2

2.
 How would you account for the following?

(i) The value of electron gain enthalpy with negative sign for sulphur is higher than that for oxygen.

(ii) NF3 is an exothermic compound but NCl3 is endothermic compound.

(iii) ClF3 molecule has a T-shaped structure and not a trigonal planar one.

3.
 Explain the following observations giving appropriate reasons:

(i) The stability of + 5 oxidation state decreases down the group in group 15 of the periodic table.

(ii) Solid phosphorus pentachloride behaves as an ionic compound.

4.
Account for the following:

(i) NH3 is a stronger base than PH3.

(ii) Sulphur has a greater tendency for catenation than oxygen.

(iii) Bond dissociation energy of F2 is less than that of Cl2.

5.
Explain the following situations:
(i) In the structure of HNO3 molecule, the N − O bond (121 pm) is shorter than the N − OH bond (140 pm).

(ii) SF4 is easily hydrolysed whereas SF6 is not easily hydrolysed.

(iii) XeF2 has a straight linear structure and not a bent angular structure.