Question

Tarnished silver contains \( Ag_2S \). Can this tarnish be removed by placing tarnished silverware in an aluminium pan containing an inert electrolytic solution such as NaCl? The standard electrode potential for the half reaction: \[ \text{Ag}_2\text{S}(s) + 2e^- \to 2\text{Ag}(s) + S^{2-}(aq) \, (\text{E}^\circ = -0.71 \, \text{V}) \] \[ \text{Al}^{3+}(aq) + 3e^- \to \text{Al}(s) \, (\text{E}^\circ = -1.66 \, \text{V}) \]

Hint:

In electrochemical reactions, the substance with the more positive reduction potential (cathode) will be reduced, and the one with the more negative reduction potential (anode) will be oxidized.

Answer 1

The reaction involves the reduction of \( Ag_2S \) to silver, and the oxidation of aluminium to aluminium ion. The cell potential for this reaction is the difference between the reduction potential of silver and aluminium: \[ \Delta E^\circ = E^\circ_{\text{cathode}} - E^\circ_{\text{anode}} = (-0.71) - (-1.66) = 0.95 \, \text{V}. \] Since the cell potential is positive, the reaction is spontaneous, meaning that tarnish can be removed by using an aluminium pan containing NaCl.