In Tollen's test for aldehyde, the overall number of electron(s) transferred to the Tollen's reagent formula $\left[\mathrm{Ag}\left(\mathrm{NH}_{3}\right)_{2}\right]^{+}$ per aldehyde group to form silver mirror is ______. (Round off to the nearest integer).

JEE Main · 2021 · 18 Mar 2021 · Shift 2 · Aldehydes Ketones and Carboxylic Acids

In Tollen's test for aldehyde, the overall number of electron(s) transferred to the Tollen's reagent formula

[Ag (NH_{3})_{2}]^{+}

per aldehyde group to form silver mirror is ______.
(Round off to the nearest integer).

Answer: 2

Silver in Tollen's reagent is in the

+ 1

state and is deposited as the metal, so each

[Ag (N H_{3})_{2}]^{+}

ion accepts one electron. The aldehyde group is oxidised to a carboxylate, and the oxidation number of the carbonyl carbon rises from

+ 1

+ 3

, a change of two units, so two silver ions are reduced for every aldehyde group:

RCHO + 2 [Ag (N H_{3})_{2}]^{+} + 3 OH^{-} ⟶ RCOO^{-} + 2 Ag + 4 N H_{3} + 2 H_{2} O

The number of electrons transferred to the reagent per aldehyde group is

2

JEE Main · 2021 · 18 Mar 2021 · Shift 2 · Integer answer