Chapter 21, Problem 85A

Interpretation Introduction

Interpretation: The working of a zinc-copper voltaic cell needs to be explained.

Concept Introduction: A voltaic cell is an electrochemical cell in which chemical energy is converted to electrical energy. This is due to the tendency of different metals to lose electrons.

Explanation of Solution

In a zinc-copper voltaic cell, zinc tends to lose electrons as compared to copper. Here, zinc and copper metal are placed in solutions of their salts. Since zinc has more tendency to lose electrons, it will provide electrons and become a positive charge. The positive charge zinc ions then go into the solution. From the solution, the reduction of copper ions takes place and the deposition of an uncharged copper atom takes place on the copper electrode.

Here, the oxidation of zinc takes place at the anode and the reaction is represented as follows:

Anode-Oxidation reaction:

  $\text{Zn}\left(s\right)\to {\text{Zn}}^{2+}\left(aq\right)+2e$

Similarly, the reduction of copper takes place at the cathode and the reaction is represented as follows:

Cathode-Reduction reaction:

  ${\text{Cu}}^{2+}\left(aq\right)+2e\to \text{Cu}\left(s\right)$

Here, the overall cell reaction will be the sum of the above two half-cell reactions.

Overall cell reaction:

  $\begin{array}{l}\text{Zn}\left(s\right)\to {\text{Zn}}^{2+}\left(aq\right)+2e\\ {\text{Cu}}^{2+}\left(aq\right)+2e\to \text{Cu}\left(s\right)\\ \overline{\underset{¯}{\text{Zn}\left(s\right)+{\text{Cu}}^{2+}\left(aq\right)\to {\text{Zn}}^{2+}\left(aq\right)+\text{Cu}\left(s\right)}}\end{array}$

Therefore, the overall cell reaction is as follows:

  $\text{Zn}\left(s\right)+{\text{Cu}}^{2+}\left(aq\right)\to {\text{Zn}}^{2+}\left(aq\right)+\text{Cu}\left(s\right)$