Question

In view of $\Delta_rG^0$ for the following reactions :
$PbO_2 + Pb \to 2PbO, \Delta_rG^0 <\, 0 $
$SnO_2 + Sn \to 2SnO, \Delta_rG^0 > 0 $
Which oxidation state is more characteristic for lead and tin ?

• A. For lead +4, for tin +2
• B. For lead +2, for tin +2
• C. For lead +4, for tin +4
• D. For lead +2, for tin +4

Answer 1

Answer: (D)

(i) For the reaction:

$PbO _{2}+ Pb \longrightarrow 2 PbO , \Delta G^{\circ}<\,0$ i.e. $(-) ve$

means $PbO \left( Pb ^{2+}\right)$ is more stable hence it has more characteristic oxidation state.

(ii) For the reaction:

$SnO _{2}+ Sn \to 2 SnO , \Delta G^{\circ}>0$ i.e. $(+) ve$

means $SnO _{2}\left( Sn ^{4+}\right)$ is more stable than $Sn ^{2+}$ (SnO) hence is more characteristic oxidation state.

Therefore, characteristic oxidation states for lead and tin are respectively $+2$ and $+4$.