Question

Make a neatly labelled sketch to show how a brass spoon can be plated with silver. Explain, your choice of electrolyte used.

Answer 1

The brass spoon, that is to be electroplated, is washed thoroughly (with NaOH, dil. HCl, detergent and distilled water), dried and made cathode. The anode is made of a pure and clean block of silver block. The electrolyte used in the reaction is sodium silver cyanide. The dissociation of electrolyte is given by:

$$\begin{gathered} \mathrm{Na}\left[\mathrm{Ag}\right(\mathrm{CN}{)}_2]\leftrightarrow \mathrm{N}{\mathrm{a}}^{+}{+\; Ag}^{+}+2\mathrm{C}{\mathrm{N}}^{-} \\ {\mathrm{H}}_2\mathrm{O}\leftrightarrow {\mathrm{H}}^{+}+\mathrm{O}{\mathrm{H}}^{-} \end{gathered}$$

Reaction at anode: The silver anode loses electrons to form silver ions and goes into the electrolyte. The equation is:
$$\begin{gathered} \mathrm{Ag}\stackrel{}{\to }{\mathrm{Ag}}^{+}(\mathrm{into}\mathrm{electrolyte})+{\mathrm{e}}^{-} \\ (\mathrm{From}\mathrm{anode}) \end{gathered}$$

Reaction at cathode: The silver ions gain electrons from the electrode to form silver atoms, which get deposited on the brass spoon as a layer of silver. The depth of this silver coating relies on the time till which the current is passed. Then the silver plated article is removed from the electrolytic cell and washed repeatedly and dried. Equation is:
$$\begin{gathered} {\mathrm{Ag}}^{+}+{\mathrm{e}}^{-}\stackrel{}{\to }\mathrm{Ag}(\mathrm{deposited}\mathrm{on}\mathrm{brass}\mathrm{spoon}) \\ (\mathrm{From}\mathrm{electrolyte}) \end{gathered}$$