Question

Match the following substances with their corresponding properties.

• A. Deliquescence
• B. Efflorescence
• C. Hygroscopy

Answer 1

Hygroscopy is the phenomenon in which the substances absorb moisture from the surroundings, usually at room temperature. These substances do not change their state.
Examples: Sodium hydroxide $\text{(}NaOH)$, conc. sulphuric acid $\text{(}{H}_2{\text{SO}}_4)$.

Efflorescence refers to property of certain hydrated salts to lose water when left in open.
Examples: Sodium carbonate $\text{(}{Na}_2{CO}_3.10H_{2}O)$, Calcium sulphate $\text{(}{CaSO}_4.2H_{2}O)$, Copper sulphate $\left({CuSO}_4.5H_{2}O\right)$.

Deliquescence, like hygroscopy, is also a tendency to absorb moisture from the air when exposed.
Here, the substance dissolves itself in moisture and form an aqueous solution.
Examples: Calcium chloride $\text{(}{CaCl}_2)$, Ferric chloride $\text{(}{FeCl}_3)$.