There has to be a provision for ion flow between the half-reactions in order to help carry the electric charge throughout the circuit, but general mixing of the two reactions is usually avoided as long as possible. One way to do that is to place each half-reaction in its own container or "half-cell". The electrolytes in the half-cells are connected via some kind of "bridge" which allows ions to migrate from one solution to the other. The bridge can be as simple as a piece of moistened filter paper (as we saw in the lab) or a more sophisticated semi-porous material which allows slow diffusion in both directions. Or, it could be a classic U-tube filled with an electrolyte and plugged with cotton at each end.

Generally metals or other conductors are placed in different electrolytes in each half-cell. It is common to use an electrolyte which contains the metal in ion form, but this is not absolutely necessary. In order to compare experimental results with standard measures, however, this is the type of cell we will look at. The metal electrodes themselves are then connected via wires to some electrical device.