Chapter 21, Problem 89A

Interpretation Introduction

Interpretation: Whether half-reactions in an electrochemical cell used to plate gold onto an object takes place if electric current is not supplied to the cell or not needs to be explained.

Concept Introduction: In electrolytic cells, an electric current makes a non-spontaneous redox reaction take place. The process by which electrical energy is converted to chemical energy is known as electrolysis. An application of electrolytic cells is electroplating. In this method, a metal can be plated on another metal. Here, the metal used for plating must have a higher tendency to undergo oxidation as compared to the metal on which plating is done.

Explanation of Solution

An electrolytic cell is used to convert electrical energy to chemical energy. Here, direct current is used to make a nonspontaneous reaction to proceed in the forward direction.

To plate gold onto an object, the negative electrode of the power source is connected to the object and the positive electrode is connected to the gold metal. Here, gold acts as an anode, and oxidation of gold takes place. Due to the oxidation of the gold, gold ions come to the solution, and the reduction of gold takes place at the cathode where it gets plated on the object.

Thus, the positive charge electrode is the anode where oxidation takes place and the negative charge electrode is the cathode where reduction takes place.

The two half-reactions can be represented as follows:

Anode: $\text{Au}\left(s\right)\to {\text{Au}}^{3+}\left(aq\right)+3e$

Cathode: ${\text{Au}}^{3+}\left(aq\right)+3e\to \text{Au}\left(s\right)$

The flow of electrons takes place from the positive electrode to the negative.

Thus, if no current is supplied to the cell, gold cannot be plated onto the object, and the electroplating process cannot take place.