**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

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.

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

###### Question

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

###### Answer

The calomel electrode cell notation can be written as

or

The comma separating *Hg _{2}Cl_{2}* 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:

or simply

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