Question

Describe an experiment to show that colloidal particles carry a particular type of electrical charge.

Answer 1

To demonstrate that colloidal particles carry a particular type of electrical charge, an experiment called cataphoresis is performed. In this experiment, a colloidal solution such as arsenic sulphide sol (As₂S₃) is taken in a U-tube, and two platinum electrodes are inserted into it,one at each end. These electrodes are connected to a battery to pass direct current through the solution. When the current is switched on, the colloidal particles begin to migrate toward one of the electrodes. In the case of arsenic sulphide sol, the particles move towards the positive electrode (anode), which clearly indicates that they carry a negative charge. This movement of colloidal particles under the influence of an electric field confirms that colloidal particles possess a definite electrical charge, either positive or negative, depending on the nature of the sol. This phenomenon is known as cataphoresis.