When current flows through a conducting solution, chemical reactions are caused. As a result, gas bubbles are formed on the electrodes.
Aim: To decompose water into hydrogen and oxygen
Procedure:

● Take out two carbon rods from discarded cells and clean them with sandpaper.

● Make carbon rods as electrodes by connecting them to a battery after wrapping copper wire around them.

● Take a full cup of water in glass bowl or plastic bowl.

● Add few drops of lemon juice or a teaspoon of salt to the water. This will make it more conducting.

● Immerse the carbon rods into the water such that the metal caps of rod are outside the water.

● Wait for few minutes.

You will observe gas bubbles near the electrodes. The hydrogen is formed on the negative electrode and Oxygen is formed on the positive electrode.