Cell notation

Cell notation in chemistry is a shorthand way of expressing a certain reaction in an electrochemical cell. The cell anode and cathode (half-cells) are separated by two bars or slashes representing a salt bridge, with the anode on the left and cathode on the right. Individual solid, liquid or aqueous phases within each half-cell are separated by a single bar. Concentrations of dissolved species, in each phase written in parentheses and the state of each phase (usually s (solid), l (liquid), g (gas) or aq. (aqueous solution)) is included in a subscript after the species name.

Examples

This illustrates a Silver (Ag) - Cadmium (Cd) cell defined by the following half reactions, with 0.010M Cadmium chloride (CdCl₂) as electrolyte. The Mercury (Hg) does nothing except act as an amalgam.

Cathode reaction

AgCl(s) + e- --> Ag(s) + Cl^-(aq) E = 0.222V

Anode reaction

Cd(s) --> Cd²⁺(aq) + 2e- E = +0.403V

Cell notation

Cd(s), Hg(s) | CdCl₂(aq)(0.010M) || AgCl(s) , Ag(s) E = 0.7585V

Note

This cell has a non-standard electric potential due to the concentration (0.010M) and the mean activity coefficient (0.513).

Other Examples

The Zinc-Hydrogen Cell

Zn | ZnSO₄(aq) || HCl(aq) | H₂(g, p=101.3 kPa) | Pt

Some gas electrodes

Pt | Cl₂, HCl (aq, 0.1 mol L^-1)

Pt | H₂, H₃O⁺ (aq, 1 mol L^-1)