Question

An electrolytic solution contains ${\mathrm{Al}}^{3+}$, and ${\mathrm{Au}}^{3+}$ ions. If the solution is electrolysed, ________ ion would be deposited at the ________.

• A. Au, cathode
• B. Al, anode
• C. Au, anode
• D. Al, cathode

Answer 1

The correct option is A Au, cathode

$\bullet$ ${\mathrm{Al}}^{3+}$ and $\mathrm{Au}{}^{3+}$ are ions of the same charge present in a solution. Thus, the ions would be preferentially discharged.

$\bullet$ According to the electrochemical series, the sequence of the cations in the decreasing order of ease of reduction would be: $\mathrm{Au}{}^{3+}$ > ${\mathrm{Al}}^{3+}$

$\bullet$ Therefore, $\mathrm{Au}{}^{3+}$ would be the first to be deposited at the cathode, when an electric current is passed through the solution.

The reaction at cathode is represeneted as:
​​​​​​​${\mathrm{Au}}^{3+}\left(\mathrm{aq}\right)+3e^{–}\to \mathrm{Au}\left(s\right)$​​​​​