IGCSE Chemistry 0620: Half-Equations for Silver Electroplating

A jeweller electroplates a steel bracelet with a thin, even layer of silver. The bracelet is connected as the cathode in an electrolytic cell containing aqueous silver nitrate solution, with a strip of pure silver connected as the anode.

(a) Write an ionic half-equation for the reaction that occurs at the cathode. [1]

(b) Write an ionic half-equation for the reaction that occurs at the anode. [1]

(c) Using your half-equations from (a) and (b), explain why the mass of the pure silver anode decreases while the mass of the bracelet increases as electroplating proceeds. [2]

(d) Suggest why the bracelet is thoroughly cleaned and degreased before electroplating begins. [1]

(e) State one property of silver, other than its appearance, that makes it a suitable metal to electroplate onto jewellery. [1]

Part (a): Half-equation at the cathode

The bracelet (cathode) attracts the positive $\text{Ag}^+$ ions from the solution. Each ion gains one electron (reduction) and is deposited as solid silver: $\text{Ag}^+(aq) + e^- \rightarrow \text{Ag}(s)$

Check: 1 Ag atom on each side; charge on the left is $(+1) + (-1) = 0$ , matching the neutral $\text{Ag}(s)$ on the right.

Part (b): Half-equation at the anode

The pure silver strip (anode) dissolves. Each silver atom loses one electron (oxidation) and enters the solution as a silver ion: $\text{Ag}(s) \rightarrow \text{Ag}^+(aq) + e^-$

Check: 1 Ag atom on each side; charge on the left is $0$ , and on the right is $(+1) + (-1) = 0$ , so the equation balances.

Part (c): Explaining the mass changes

At the anode, the half-equation in (b) shows solid silver atoms turning into $\text{Ag}^+$ ions that leave the electrode and enter the solution, so silver metal is continuously removed from the anode, and its mass decreases.

At the cathode, the half-equation in (a) shows $\text{Ag}^+$ ions from the solution gaining an electron and becoming solid silver, which stays on the electrode, so silver metal is continuously added to the bracelet, and its mass increases.

Because one $\text{Ag}^+$ ion is produced at the anode for every one deposited at the cathode, the concentration of $\text{Ag}^+$ ions in the solution stays roughly constant throughout.

Part (d): Why the bracelet is cleaned first

Any grease, oil or dirt on the bracelet’s surface would act as a barrier between the steel and the electrolyte, preventing silver ions from being deposited evenly at that point. Cleaning and degreasing the surface first ensures the silver coating bonds firmly and evenly over the whole bracelet, rather than being patchy or flaking off.

Part (e): A useful property of silver

Besides looking attractive, silver resists corrosion far better than the steel underneath it. The silver coating therefore protects the bracelet from corroding and keeps it looking good for much longer.

Final answers

(a) $\text{Ag}^+(aq) + e^- \rightarrow \text{Ag}(s)$
(b) $\text{Ag}(s) \rightarrow \text{Ag}^+(aq) + e^-$
(c) Anode loses mass as silver atoms dissolve into solution as ions; cathode (bracelet) gains mass as silver ions are deposited as solid silver.
(d) So the silver coating sticks firmly and evenly, rather than flaking off a greasy/dirty surface.
(e) Silver resists corrosion better than steel, protecting the bracelet.