Metal–metal ion half-cells
A simple half-cell consists of a metal electrode in contact with an aqueous solution containing ions of that metal. Connecting two different half-cells allows their potential difference to be measured.
Suitable combinations can use metals such as zinc, copper, iron or silver with their corresponding soluble metal-ion solutions. A concentration of is commonly used when setting up these cells.
Preparing the electrodes
- Rub each metal strip with sandpaper or emery paper to remove oxide from the surface.
- Grease can also be removed from the electrode before use.
- Place each metal in a solution containing its own ions.
- A long strip can be folded over the edge of the beaker to give a secure point for the crocodile clip.
Half-cells without a metal electrode
If the redox system contains only dissolved species, there is no conducting metal belonging to the redox pair. For example, an half-cell can use an inert platinum electrode. Platinum provides electrical contact but does not take part in the redox reaction.
Exam Tip: A metal–metal ion half-cell needs the metal and a solution containing its ions. If both members of the redox pair are dissolved, state that an inert conducting electrode such as platinum is required.