Question

A solution at 25°C contains 1.0 M Cd²+, 1.0 M Ag⁺,1.0 M Au³⁺, and 1.0 M Ni²⁺ in the cathode compartment of an electrolytic cell. Predict the order in which the metals will plate out as the voltage is gradually increased.

Short answer

The order of the metal will plate out with the gradual increase in voltage is$A{u}^{3+}>A{g}^{+}>N{i}^{2+}>C{d}^{2+}.$

Step-by-step solution

Reaction of reduction for cadmium and silver

The reaction of reduction for Cadmium with -0.4 V can be denoted as:

$C{d}^{2+}+2e^{-}\to Cd$

The reaction of reduction for silver with 0.8 V can be denoted as:

$Ag+e^{-}\to Ag$

Reaction of reduction for gold and nickel

The reaction of reduction for Gold with 1.5 V can be denoted as:

$A{u}^{3+}+3e^{-}\to Au$

The reaction of reduction for nickel with -0.23 V can be denoted as:

$N{i}^{2+}+2e^{-}\to Ni$

The metal with high reduction potential will remove first. Therefore, the order of the metal will plate out as the voltage is gradually increased.$A{u}^{3+}>A{g}^{+}>N{i}^{2+}>C{d}^{2+}.$