Question

Why is the gas with higher critical temperature easily adsorbed on activated alumina?

Answer 1

Easily liquefiable gases get adsorbed to more extent. Nature of gas is responsible for adsorption of gases on the solid or liquid surface. Alumina is a great adsorbent with high adsorbing properties. Activated alumina is a porous material.

Complete step by step answer:
Gases can be converted to liquids by compressing the gas at a suitable temperature. Gases become more difficult to liquefy as the temperature increases because the kinetic energies of the particles that make up the gas also increase.
The critical temperature of a substance is the temperature at and above which vapor of the substance cannot be liquefied, no matter how much pressure is applied. Every substance has its own unique critical temperature. It can also be defined as the temperature at which the substance can exist as a liquid.
Adsorption is the process where molecules stick to the surface of a solid, so adsorption of gases is when gas molecules stick to the surface of a solid.

The extent of adsorption of a gas on a solid surface is affected by the following factors:
(1) Nature of the gas
(2) Nature of adsorbent
(3) Specific area of the adsorbent
(4) Effect of temperature
(5) Effect of pressure
(6) Activation of adsorbent.

However, out of all these factors, Above its critical temperature a gas cannot be liquefied, and therefore the nature of gas is responsible here. Easily liquefiable gases(i.e. with higher critical temperature) are readily adsorbed. Thus 1g of activated charcoal adsorbs more sulphur dioxide (critical temperature 630K) than methane (critical temperature 190K).

Note: Out of all the periodic elements, Xenon of p-block is most easily liquefiable rare gas because interatomic interactions increase with increasing atomic number. Every substance has its own unique critical temperature.