Question

Conc. ${H_2}S{O_4}$ is not a/an:
(A) Efflorescent
(B) Dehydrating agent
(C) Sulfonating agent
(D) Hygroscopic

Answer 1

Hint: Dehydrating agent is a compound which can remove water from substances. Hygroscopic compound is a compound which absorbs water from the atmosphere. Efflorescent compound is the compound which has water associated with its molecules and it loses the water molecules when exposed to air.

Complete Step-by-Step Solution:
We will get information about different characteristics of concentrated sulphuric acid solution.
- We know that ${H_2}S{O_4}$ (sulphuric acid) is a strong acid. It can act as an acid because it can donate protons and accept electrons. Sulphuric acid is also called the king of chemicals because of its wide variety of uses and importance.
 - Sulphuric acid can act as a dehydrating agent. Dehydrating agent is a compound which can dehydrate the substance. ${H_2}S{O_4}$ has strong affinity towards water and thus it can remove water molecules from certain substances which have them.
- We know that sulphuric acid can form sulfonate ions in its solution. These sulfonate ions can act as an electrophile for aromatic electrophilic substitution reaction. Thus, we can say that concentrated ${H_2}S{O_4}$ is a good sulfonating agent.
- Hygroscopic compound is a compound which absorbs water from the atmosphere. Thus, it can absorb moisture from the atmosphere and become slightly dilute upon dissolution. Sulphuric acid also shows the same property.
- Efflorescent compound is the compound which has water associated with its molecules and it loses the water molecules when exposed to air. Concentrated sulphuric acid actually accepts water molecules from air. So, we can say that sulphuric acid is not an efflorescent compound.

Thus, the correct answer of the equation is (A).

Note: Do not get confused between oleum and concentrated sulphuric acid. Actually, oleum contains $S{O_3}$ (Sulphur trioxide) dissolved in concentrated sulphuric acid. Concentrated sulphuric acid does not contain water.