Chapter 21, Problem 41A

Interpretation Introduction

Interpretation: The electrical potential of a standard hydrogen electrode needs to be determined.

Concept Introduction: Electrical potential is defined as a measure of the ability of the cell to produce an electric current. It is measured in volts (V). For an isolated half-cell, electrode potential cannot be calculated. When two half-cells are connected to form a voltaic cell, the difference in the potential is measured.

Explanation of Solution

The cell potential of a half-cell cannot be measured thus, a reference electrode is required for its calculation. The standard hydrogen electrode is used for this purpose because its reduction electrode potential is 0.0 V. Here, the hydrogen electrode can be used with other electrodes to calculate their reduction potentials.

In a standard hydrogen electrode, the platinum electrode is immersed in a solution with a concentration of hydrogen ion 1.0 M. Hydrogen gas is bubbled around the platinum electrode at a pressure 101 kPa.

The half-cell reaction that takes place is as follows:

  $2{\text{H}}^{+}\left(aq,\text{ 1M}\right)+2e\rightleftharpoons {\text{H}}_2\left(g,101\text{ kPa}\right)E_{{\text{H}}^{+}}^o=0.0\text{ V}$

The above reaction is reversible. The standard electrode potential is the tendency of hydrogen ions to gain electrons and to get reduced to hydrogen gas.