Question

Explain how the adsorption of gas on solid varies with :

a. nature of adsorbate and adsorbent 

b. surface area of adsorbent

Answer 1

i. a. Nature of adsorbate :

1. All solids adsorb gases to some extent. It is observed that gases having high critical temperature liquify easily and can be readily adsorbed.

2. The gases such as SO₂, Cl₂, NH₃ which are easily liquefiable are adsorbed to a larger extent as compared to gases such as N₂,O₂,H₂, etc. which are difficult to liquify.

3. Thus, the amount of gas adsorbed by a solid depends on the nature of the adsorbate gas i.e., whether it is easily liquefiable or not.

b. Nature of adsorbent :

Substances which provide large surface area for a given mass are effective as adsorbents and adsorb appreciable volumes of gases. 

e.g.,

Silica gel and charcoal are effective adsorbents due to their porous nature.

ii. Surface area of the adsorbent :

• Adsorption is a surface phenomenon. Hence, the extent of adsorption increases with increase in surface area of the adsorbent.
• Finely divided substances, rough surfaces, colloidal substances are good adsorbents as they provide larger surface area for a given mass.

Note : Critical temperature of some gases and volume adsorbed.