Cell notation

Cell notation is a shorthand representation of an electrochemical cell.

For example, the electrochemical cell depicted in the diagram above has a cell notation of

Pt\mid H_2\mid H^+ \parallel Cu^{2+}\mid Cu

A vertical line represents a phase boundary, while a double vertical line signifies a phase boundary with negligible junction potential, e.g. a salt bridge. The anode half-cell is denoted on the left and the cathode half-cell on the right, with the electrodes positioned at both ends. A gas is always written adjacent to the electrode. Spectator ions are usually omitted and state symbols and concentrations may be included for emphasis, e.g.

Pt(s)\mid H_2(g)\mid H^+(aq,1\, M) \parallel Cu^{2+}(aq,1\, M)\mid Cu(s)

If the standard hydrogen electrode is undergoing reduction, its cell notation is:

Zn\mid Zn^{2+}\parallel H^+ \mid H_2\mid Pt



What are the cell notations for a calomel reference electrode undergoing oxidation and a AgCl electrode undergoing reduction?


The calomel electrode cell notation can be written as

Hg\mid Hg_2Cl_2(sat'd),KCl(sat'd)\mid KCl(sat'd)\parallel


Hg\mid Hg_2Cl_2(sat'd),KCl(sat'd)\parallel

The comma separating Hg2Cl2 and KCl means that the two compounds are in the same phase. The double vertical line represents the porous frit, which has negligible junction potential.

The AgCl electrode cell notation is:

\parallel KCl(sat'd),AgCl(sat'd)\mid AgCl\mid Ag

or simply

\parallel KCl(sat'd),AgCl(sat'd)\mid Ag



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