Electrochemical cells made from two half-cells
You can produce electricity from a cell which is made of two different metals where the metals are dipping into solutions of their own ions.
A simple cell has some essential features:
- It is made of two different metals.
- The metals are separated from each other by an electrolyte.
- The metals are connected by wires through which electrons can flow.
An example of zinc and copper being used to make a cell can be seen in the diagram below.
The zinc is higher in the electrochemical series, so it pushes electrons towards the copper.
\(Zn(s) \to Zn_{}^{2 + }(aq) + 2e_{}^ - \)
The ions of the less reactive copper are forced to accept these electrons:
\(Cu_{}^{2 + }(aq)(blue\,ions) + 2e_{}^ - \to Cu(s)(brown\,metal\,powder)\)
The purpose of the ion bridge is to complete the circuit of this cell. The ion bridge (sometimes called a salt bridge) contains an electrolyte which takes no part in the cell reactions.
The chemical reactions in cells like these are displacement reactions. Zinc can displace copper from copper(II) sulfate solution. If a displacement reaction is made to happen in a cell then useful energy in the form of electricity can be produced.