Electrochemical cells
Electricity from pairs of metals
When metals give away their electrons, they do so with a certain force. This force is measured in volts. When two different metals are connected together in a cell, the metal with the higher force pushes its electrons on to the other metal.
A simple electrochemical cell can be produced by dipping two different metals into an electrolyte and connecting them via wires and a voltmeter, bulb, motor, etc.
Watch this demonstration of electrochemical cells made using different metals
The image below shows what happens in a cell that is made from magnesium and copper in a beaker of ammonium chloride solution.
The two metals produce an electric current. Magnesium is higher up the electrochemical series than copper, so the magnesium can push away its electrons more strongly than copper. Electrons flow along the wires and through the voltmeter from the magnesium to the copper.
The voltmeter measures the force that pushes the electrons through the wires. If you replaced the magnesium in this cell with other metals you would obtain different voltage readings. By arranging the metals in order of their voltage readings, you can build up the electrochemical series.
Using different combinations of metals in a cell lets you produce a cell with a voltage which is appropriate for the circuit it will be connected to. Sometimes you want a larger voltage, sometimes smaller.
The further apart the metals are in the electrochemical series, the higher the voltage. Electrons flow along the wire from the metal higher in the electrochemical series to the metal lower down.
To understand how electricity is made from pairs of metals the following points must be understood:
- A cell is an arrangement where electricity is generated from a chemical reaction.
- An electrolyte is a liquid that conducts electricity. In the magnesium/copper cell the electrolyte is an ionic solution - ammonium chloride in water. The electrolyte completes the circuit in the cell.