Take out carbon rods carefully from two discarded cells. Clean their metal caps with sand paper. Wrap copper wires around the metal caps of the carbon rods and join them to a battery (Fig.). We call these two rods electrodes. (Instead of carbon rods, you may take two iron nails about 6 cm long.) Pour a cupful of water in a glass/ plastic bowl. Add a teaspoonful of salt or a few drops of lemon juice to water to make it more conducting. Now immerse the electrodes in this solution. Make sure that the metal caps of the carbon rods are outside the water. Wait for 3-4 minutes. Observe the electrodes carefully. Do you notice any gas bubbles near the electrodes? Can we call the change taking place in the solution a chemical change? Recall the definition of a chemical change that you learnt in Class VII.
On passing electric current through the conducting solution of lemon juice and water, chemical reaction takes place. Water is dissociated into its constituent gases, i.e., hydrogen and oxygen. Oxygen bubbles are formed on the electrode connected to the positive terminal of the battery and hydrogen bubbles are formed on the other electrode. Changes of colour of solutions may occur depending on what solution and electrodes are used. This process is known as chemical effects of current.