Question

Which of the following is an example of absorption?
A ) Water on silica gel
B ) Water on calcium chloride
C ) Hydrogen on finely divided nickel
D ) Oxygen on metal surface

Answer 1

Hint: Adsorption is the surface phenomenon whereas absorption is the bulk phenomenon. In adsorption, the adsorbate molecules remain on the surface of the adsorbent. On the other hand, in absorption, the adsorbate molecules penetrate the bulk of the adsorbent.

Complete answer:
Let us find out the absorption process in the given option:
> Water on silica gel is an example of adsorption. Water molecules remain on the surface of silica gel. Water molecules do not enter the bulk of silica gel.
> During absorption, the adsorbate molecules penetrate the bulk of the adsorbent.
Water on calcium chloride is an example of absorption. This is because water is added to the calcium carbonate, water goes in the bulk of the calcium carbonate.
> Hydrogen on finely divided nickel is an example of adsorption. Hydrogen remains on the surface of finely divided nickel. Hydrogen molecules do not enter the bulk of finely divided nickel.
> Oxygen on a metal surface is an example of adsorption. Oxygen remains on the surface of metal. Oxygen molecules do not enter the bulk of metal.

Hence, the correct option is the option B ).

Note: Absorption is an endothermic process. Heat energy is absorbed during absorption.
Adsorption is an exothermic process. Heat energy is given out during adsorption. During absorption, the concentration is uniform throughout, whereas during adsorption, the concentration at the surface is much higher than the concentration in the bulk.