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.

Some examples of this notation are:

Zn°|Zn²⁺,Cl⁻|AgCl|Ag°. This means that the left electrode (anode) is made of zinc, while the other one (right, cathode) is composed of a silver wire covered by a silver chloride layer which is not soluble. Both of the electrodes are immersed into aqueous media where are present zinc and chloride ions.

Zn°|Zn²⁺, SO₄²⁻||SO₄²⁻|Cu²⁺|Cu°. This cell is very famous: The Daniell cell. If the electrodes are connected, a spontaneous reaction takes place. Zinc is oxidized, and copper ions are reduced.

Sometimes the state of each species into the cell is written. For example in the zinc cell (showed above), we can write that zinc, silver and silver chloride are solids, while zinc cation and chloride anion are in aqueous media. So, the new notation will be:

Zn°(s)|Zn²⁺(aq),Cl⁻(aq)|AgCl(s)|Ag°(s)

It is possible to express the ion concentration too. For example, in the Daniell cell:

Zn°(s)|Zn²⁺(aq, 1 mol/L), SO₄²⁻(aq, 1 mol/L)||SO₄²⁻(aq, 1 mol/L)|Cu²⁺(aq, 1 mol/L)|Cu°(s)

In this case, all ions (sulfate, zinc and copper) are in a concentration equal to 1 mol/L.