Q.Distinguish between the following:
Adsorption and absorption. Give one example.

The substance being adsorbed is the adsorbate; the surface on which it collects is the adsorbent.

In adsorption, two substances are involved:

• Adsorbent: the solid (or liquid) surface on which adsorption takes place
• Adsorbate: the substance (gas or dissolved solute) that gets adsorbed, i.e. that accumulates, on the surface of the adsorbent …

Physisorption is a reversible surface phenomenon held together by weak van der Waals forces, not by chemical bonding.

Adsorption is the accumulation of molecules of a gas or liquid (the adsorbate) on the surface of a solid or liquid (the adsorbent), so that the concentration at the surface becomes higher than in the bulk.

When the attractive forces between the adsorbate and the adsorbent surface are weak van der Waals forces (dispersion/dipole forces) rather than a chemical bond, the phenomenon is called physical adsorption (physisorption).

Key characteristics:

• Not specific — any gas is adsorbed to some extent on any solid.
• Reversible — the adsorbed gas can be removed easily by heating or lowering the pressure.
• Low enthalpy of adsorption, about 20–40 kJ/mol.
• Decreases as temperature increases. …

The substance whose molecules accumulate on a surface is the adsorbate; the surface (here, activated charcoal) on which it accumulates is the adsorbent.

In adsorption, two substances are involved:

• Adsorbent — the solid (or liquid) surface on which accumulation of molecules occurs. Here, activated charcoal is the adsorbent.
• Adsorbate — the substance whose particles get adsorbed on the surface of the adsorbent. Here, acetic acid molecules accumulate on the charcoal surface, so acetic acid is the adsorbate. …

Activated charcoal's huge surface area lets it adsorb toxic mine gases before they reach the miner's lungs.

Activated charcoal is charcoal that has been treated to produce a very large number of tiny pores, giving it an enormous internal surface area (hundreds of square metres per gram).

Coal mines contain dangerous gases such as carbon monoxide (CO), methane, and other poisonous fumes. When air is drawn through a gas mask packed with activated charcoal, the toxic gas molecules stick to the charcoal's surface by physical adsorption (weak van der Waals forces between the gas molecules and the carbon surface), rather than reacting chemically with it.

…