Electrolysis
Description
A pair of copper electrodes are connected to a source of electrical power and placed in a conductive solution. After a while the solution turns a pale blue.
Requires
- Two pieces of copper: the electrodes – lengths of copper pipe work well.
- Means to connect the electrodes to the current source.
- Wires and connectors to make the circuit.
- Power source.
- A transparent container (such as those available in The Shop)
- A conductive solution (e.g. salt in water)
This requires preparation of some electrical connections. Wires may be soldered to the copper pipe but I find hose clips (Jubilee clips) work well to make these connections.
Method
Dissolve your chosen salt in some water in your transparent container. Place the electrodes in the solution, connect up the electrodes to the power supply so the solution forms part of the circuit. Turn on the power supply and wait for a while. Bubbles should form on one electrode immediately. After a while solution should start to turn a light blue colour as the copper is oxidised and copper ions dissolve in the water.
Principle
The electrical current means that copper is oxidised at one electrode and hydrogen is reduced at the other. The copper forms the Cu2+ ion which is a pale blue when it is dissolved in water. Hydrogen gas can be seen bubbling off one of the electrodes.
The amount of copper that dissolves depends on the current that flows and how long it flows for.
Tip
Common salt is a very convenient way to produce a conducting solution. The only problem is that this tends to result in the formation of insoluble copper compounds. I recommend using Epsom salts as the products are much more soluble and therefore do not obscure the colour of the solution.
There are many current sources which are suitable for this. For ease and portability I use a pack of ten 1.5 V AA size batteries. When they are fresh it delivers sufficient current to have a visible colour in a couple of minutes. I have also used 9 V PP3 batteries, but these drain very quickly. The best source I have used is a car battery charger. As this can deliver high currents one has to be very careful with the electrodes to ensure that they are not in contact.
I have my electrodes in close proximity but not touching by using cable ties in a figure eight pattern at the top and bottom to fix them together. This give enough clearance between the two sections of pipe. for the hose clips if they are offset from one another.
Safety
The current flowing may be large depending on the power source. Appropriate measures should be taken to prevent shorts. If the battery pack is shorted out the temperature of the batteries will tend to rise, but in most cases this will increase the internal resistance which will in turn limit the current which is being delivered.
Hydrogen gas is being evolved at one of the electrodes. Avoid sources of ignition and ensure the experiment is done in a well ventilated space.