Question

Gas masks work on the principle of:
[A] Chemical adsorption
[B] Physical adsorption
[C] Both chemical and physical adsorption
[D] None of these.

Answer 1

Hint: Gas masks use activated charcoal or mixture of adsorbents. Charcoal is activated by reacting it multiple times with oxygen which leads to the formation of low volume pores for adsorption. We can also treat activated charcoal with certain chemicals to get protection from a certain kind of gas or even liquid.

Complete step by step solution:
We know that gas masks are used to protect us from airborne pollutants especially during chemical or biological attacks or even in industries like the paint industry to protect workers from damaging chemicals in paint and many other industries.
These gas masks work on the principle of adsorption. We know that adsorption is the process of deposition of a particular substance on the surface of some other substance and not in its bulk.
There are different kinds of gas masks which are used for different purposes and work on different working principles.
Generally, we use activated charcoal for the adsorption of gases like $C{{l}_{2}},C{{O}_{2}}\text{ or S}{{\text{O}}_{2}}$ . The gas is adsorbed at the surface of the adsorbent.
To answer this question, let us first understand what chemical and physical adsorption are.
If the gas is accumulated on the surface of solid by weak van der Waal’s forces, the adsorption is termed as physical adsorption. If the gas molecules are held on the surface of the adsorbent by chemical bonds, then the adsorption is called chemical adsorption.
Now, let us discuss how activated charcoal is used in a gas mask.
We know that charcoal is carbon. In activated charcoal, the charcoal is reacted with oxygen many times which opens up millions of pores on its surface. Thus, activated charcoal becomes highly porous and opens many binding sites. Activated charcoal also has a larger surface area therefore, it is an effective adsorbent. The gas molecules are physically attached to the surface of activated charcoal and thus the air that passes is pure and safe to breathe. But chemisorption can also take place if the activated charcoal is treated with certain chemicals for adsorption of certain kinds of gases. Thus, it works on the principle of chemisorption as well as physisorption.

Therefore, the correct answer is option [C] both chemical and physical adsorption.

Note: There are certain cases where physical adsorption, as well as chemical adsorption, takes place simultaneously. At low temperature, physical adsorption may convert into chemical adsorption as the temperature increases. For example, on the surface of nickel, hydrogen molecules were attached through weak van der Waals forces but then the molecules dissociated to form hydrogen atoms which were held by chemical adsorption on the surface.