Concepts of Physics

IIT JEE Physics (1978-2018: 41 Years) Topic-wise Complete Solutions

Electrolysis of Saline Water


To learn about electrolysis


Carbon rods from dry cell, 9 V battery, a plastic container, connecting wires, CD.


Take a CD and make it transparent by scarping on one side. Make two hole at a distance of 3-4 cm so that carbon rods can be inserted into these holes. Connect carbon rods to the battery. Identify the positive and negative terminals. Now fill the plastic container with pure water and insert the rods into it. What do you observe? Now mix some salt into the water and repeat the observation? Do you find some change?



Pure water is poor conductor of electricity as compared to salt solution. Thus you observe less number of bubbles in first case. In second case you will find more number of bubbles. You will observe that more bubbles are coming from one rod as compared to other rod. Write the equations for chemical reaction? The gases produced are hydrogen and oxygen? Which gas is produced at positive terminal? Why there are more number of bubbles on one rod?