Ncert Exercises & Solutions

Three pairs of compounds are given below. Identify that compound in each of the pairs which has group 13 element in more stable oxidation state. Give reason for your choice. State the nature of bonding also.

1. TlCl₃, TlCl

2. AlCl₃, AlCl

3. InCl₃, InCl

(a) TlCl more stable than TlCl₃ due to inert pair effect. TlCl₃ is less stable and covalent in nature but TlCl is more stable and ionic in nature.

(b) Due to absence of d-orbitals, Al does not show inert pair effect. Hence, its most stable oxidation state is +3. Thus, AlCl₃ is much more stable than AlCl. Further, in the solid or the vapour state, AlCl₃ covalent in nature but in aqueous solutions, it ionises to form a Al³⁺ (aq) and Cl^- (aq) ions.

(c) Due to inert pair effect, indium exists in both +1 and +3 oxidation states out of which +3 oxidation state is more stable than +1 oxidation state. In other words, InCl₃ is more stable than InCl. Being unstable, InCl undergoes disproportionation reaction.

3 InCl (aq) \to 2 In (s) + {In}^{3 +} (aq) + 3 {Cl}^{-} (aq)

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