Question

In Tollen’s test for aldehyde, the overall number of electron(s) transferred to the Tollen’s reagent formula $[\mathrm{Ag}{\left({\mathrm{NH}}_3\right)}_2{]}^{+}$ per aldehyde group to form silver mirror is ________. (Round off to the Nearest Integer).

Answer 1

1. One mole of aldehyde reacts with Tollen’s reagent to the form one mole of carboxylic acid, two moles of silver and two moles of ammonia.
2. Reaction: The first half of the reaction:$[\mathrm{Ag}{\left({\mathrm{NH}}_3\right)}_2{]}^{+}+{\mathrm{e}}^{-}⟶{\mathrm{Ag}}^0+2{\mathrm{NH}}_3$.
3. The second half of the reaction: $\mathrm{RCHO}+3{\mathrm{OH}}^{-}⟶{{\mathrm{RCO}}_2}^{-}+2{\mathrm{H}}_2\mathrm{O}+2{\mathrm{e}}^{-}$.
4. Overall reaction: $2[\mathrm{Ag}{\left({\mathrm{NH}}_3\right)}_2{]}^{+}+\mathrm{RCHO}+3{\mathrm{OH}}^{-}⟶2{\mathrm{Ag}}^0+{{\mathrm{RCO}}_2}^{-}+4{\mathrm{NH}}_3+2{\mathrm{H}}_2\mathrm{O}$.
5. In the above reaction, $2{\mathrm{Ag}}^{+}+2{\mathrm{e}}^{-}\to 2\mathrm{Ag}$.

Thus, the total number of electrons transferred is 2.