PHYSICAL CHEMISTRY IN BRIEF

CHAP. 11: ELECTROCHEMISTRY [CONTENTS] 404

11.8.10.1 Amalgam half-cell

In this half-cell the electrode is formed by mercury in which a metal is dissolved. The electrolyte
contains the cations of this metal.

Example

An electrode is formed by cadmium dissolved in mercury. The molality of the dissolved cadmium

is denotedm 1. The electrolyte is an aqueous solution of cadmium sulfate. The molality of the

Cd2+ions in the solution is denotedm 2.

Reaction:

Cd2++ 2 e−= Cd.

Nernst equation:

Φ = Φ◦−

RT

2 F

ln

m 1 γCd

m 2 γ±

.

11.8.10.2 Half-cell of the first type

The electrode is formed by a metal, with the electrolyte containing the cations of this metal.

Example

A copper electrode is dipped into a solution of copper sulfate of the molalitym.

Reaction:

Cu2++ 2 e−= Cu.

Nernst equation:

Φ = Φ◦−

RT

2 F

ln

mst

mγ±

.

11.8.10.3 Half-cell of the second type

Half-cells of the second type are formed by a metal electrode coated with a layer of a sparingly
soluble salt whose cation is the given metal. The electrode is dipped into an electrolyte which
has the same anion as the sparingly soluble salt.