Introduction to copper plating

Class practical

An opportunity to investigate the deposition of solids and gases at the electrodes immersed in a solution.

Apparatus and Materials

For each student group

• Cells, 1.5 V, with holders, 3
• Crocodile clips, 2
• Lamps with holders, 2
• Ammeter (0 - 1 amp), DC
• Leads, 4 mm, 7
• Beaker, 250 ml (or 150 ml, tall form)
• Electrodes - pairs of carbon rods and strips of copper foil, width 1 cm
• Hardboard disc (to cover beaker) with holes (to take electrodes)
• Copper sulfate solution, 0.5 M

Health & Safety and Technical Notes

Modern dry cell construction uses a steel can connected to the positive (raised) contact. The negative connection is the centre of the base with an annular ring of insulator between it and the can. Some cell holders have clips which can bridge the insulator causing a short circuit. This discharges the cell rapidly and can make it explode. The risk is reduced by using low power, zinc chloride cells not high power, alkaline manganese ones.

Read our standard health & safety guidance

The carbon rods can be pencil ‘leads’.

The strips of copper foil should be 2 cm longer than the depth of the beaker.

A cheaper alternative to the copper sulfate solution is a 50:50 mixture of 0.1 M copper sulfate and 0.2 M sodium chloride.

Procedure

1. Fit the two strips of copper foil inside the beaker as shown, with the top 2 cm bent back over the edge of the beaker.
2. Use two crocodile clips to keep the foils in place. Connect leads to the clips.
3. Half-fill the beaker with copper sulfate solution.
4. Complete the circuit as shown. Let the current run for some minutes and then look at the strips to see if there is any difference.
5. Repeat using the carbon electrodes. These pencil leads will slip through the holes drilled in the beaker lids, and can be kept in place with the crocodile clips.

Teaching Notes

• Bare copper wire electrodes are not satisfactory for copper plating. The initial current density would likely be so high that the oxygen produced would then reduce the current.
• Copper sulfate is a chemical compound containing copper, sulfur and oxygen. By using first copper electrodes and then carbon electrodes, the students can be encouraged to conclude that copper is being deposited at one side. This may prompt them to ask what is happening at the other side.
• If the terminals of the copper electrodes are reversed, copper will go into solution at the positive electrode and be deposited at the negative electrode. Some form of copper is travelling from one electrode to the other, through the solution. Electric current is also passing between the electrodes. Say, there may be some things made of copper making up the current in the solution.
• Scientists believe that there are charged carriers in a conducting solution. They give these the old Greek name for travellers: ions. If the charged particle is travelling from the red terminal (also called the positive terminal) of the cell through the liquid to the black terminal (also called the negative terminal) of the cell, then it is said to be a positive particle. This is the origin of the convention that electric current flows from positive to negative; we call this conventional current as a short-hand.

This experiment was safety-tested in December 2004