Question

A metal article is to be electroplated with silver. The electrolyte selected is sodium argentocyanide.
(a) What kind of salt is sodium argentocyanide?
(b) Why is it preferred to silver nitrate as an electrolyte?
(c) State one condition to ensure that the deposit is smooth, firm and long lasting.
(d) Write the reaction taking place at the cathode.
(e) Write the reaction taking place at the anode.

Answer 1

(a) Sodium argentocyanide is a complex salt.

(b) Sodium argentocyanide is preferred to silver nitrate as an electrolyte because the deposition of silver on the articles takes place slowly in the former, resulting in more smooth and uniform plating.

(c) One condition to ensure that the deposition is smooth, firm and long lasting is to make use of a low electric current ​passage (D.C. passage) for a long time during electroplating.

(d) Reaction at cathode: The silver ions gain electrons from the electrolyte to form silver atoms, that get deposited on the article as a layer of silver.
$$\begin{gathered} {\mathrm{Ag}}^{+}+{\mathrm{e}}^{-}\stackrel{}{\to }\mathrm{Ag} \\ (\mathrm{fro}\mathrm{m}\mathrm{e}\mathrm{l}\mathrm{e}\mathrm{c}\mathrm{t}\mathrm{r}\mathrm{o}\mathrm{l}\mathrm{y}\mathrm{t}\mathrm{e})\mathrm{silver}\mathrm{de}\mathrm{p}\mathrm{o}\mathrm{s}\mathrm{i}\mathrm{t}\mathrm{e}\mathrm{d}\mathrm{o}\mathrm{n}\mathrm{a}\mathrm{r}\mathrm{t}\mathrm{i}\mathrm{c}\mathrm{l}\mathrm{e} \end{gathered}$$

(e) Reaction at anode: The silver anode loses electrons into the electrolyte to become silver ions.
$$\begin{gathered} \mathrm{Ag}\stackrel{}{\to }{\mathrm{Ag}}^{+}(\mathrm{in}\mathrm{to}\mathrm{electrolyte})+{\mathrm{e}}^{-} \\ (\mathrm{silver}\mathrm{f}\mathrm{r}\mathrm{o}\mathrm{m}\mathrm{a}\mathrm{n}\mathrm{o}\mathrm{d}\mathrm{e})\mathrm{S}\mathrm{i}\mathrm{l}\mathrm{v}\mathrm{e}\mathrm{r}\mathrm{i}\mathrm{o}\mathrm{n}\mathrm{s} \end{gathered}$$