Question

Assign reasons for each of the following:
(a) Gallium (+1) undergoes disproportionation reactions.
(b) Unlike $In^{+}$, $Tl^{+}$ is more stable with respect to disproportionation.
(c) InCl undergoes disproportionation but TlCl does not.

Answer 1

i) The two oxidation states shown by gallium is +3 and +1 and this is mainly due to inert pair effect. Of the two oxidation state exhibited, +3 oxidation state is more stable and +1 oxidation state is least stable. Hence, disproportionation occurs by gallium in aqueous solution to form most stable +3 oxidation state.

The disproportionation reactions of gallium in aqueous medium is as follows,

i) Both ${ In }^{ + }$ and ${ Tl }^{ + }$ shows +1 and +3 oxidation states, but the inert pair effect is more dominant. So +3 oxidation state is more stable compared to +1 oxidation state for ${ In }^{ + }$ And in the case of ${ Tl }^{ + }$, the +1 oxidation state is more stable compared to +3 oxidation state. So, in aqueous solution, less stable +3 of ${ In }^{ + }$ under goes disproportionation to form more stable +1 state. Whereas, in ${ Tl }^{ + }$, +1 is most stable oxidation state, so it does not undergoes disproportionation reaction.

$3{ In }^{ + }(aq)\xrightarrow [ Disproportionation ] \quad 2In\quad (s)\quad +\quad { In }^{ 3+ }(aq) \\ 3{ Tl }^{ + }(aq)\quad \xrightarrow [ Not\quad Possible ] \quad 2TI(s)\quad +\quad { Tl }^{ 3+ }(aq) \\ 3TlCl(aq)\quad \xrightarrow [ Not\quad Possible ] \quad 2Tl(s)\quad +\quad { Tl }^{ 3+ }(aq)\quad +\quad 3{ Cl }^{ - }(aq)$

Similar, answer for third question also. Because ${ In }^{ + }$ undergoes disproportionation reaction to form +3 oxidation state to +1 oxidation state, whereas, the +1 oxidation of ${ Tl }^{ + }$ is stable as it does not undergo disproportionation reactions.