PHYSICAL CHEMISTRY IN BRIEF

CHAP. 11: ELECTROCHEMISTRY [CONTENTS] 410

Solution

The following reactions proceed in the cell:

1

2 H^2 (p^1 ) = H

+(a) + e− oxidation,

H+(a) + e− =^12 H 2 (p 2 ) reduction.

Nernst equation:

E=

RT

2 F

ln

p 1 φ 1

p 2 φ 2

,

whereφ 1 andφ 2 are the fugacity coefficients of hydrogen.

11.8.15 Amalgam electrode concentration cells

The cell is formed by two mercury electrodes in which the same metal of different concentrations
is dissolved. The electrodes are dipped into a shared electrolyte in which there are cations of
the given metal.

Example

Let us consider a cell formed by two cadmium amalgam electrodes dipped into a shared electrolyte

Cd(Hg)(a 1 )|CdSO 4 (a)|Cd(Hg)(a 2 ),

wherea 1 > a 2. The following reactions proceed in the cell:

Cd(a 1 ) = Cd2+(a) + 2 e− oxidation,

Cd2+(a) + 2 e− = Cd(a 2 ) reduction.

Nernst equation:

E=

RT

2 F

ln

a 1

a 2

.