Question

Which of the following is an efflorescent salt?

• A. $\mathrm{NaOH}$
• B. ${\mathrm{Na}}_2{\mathrm{CO}}_3.10{\mathrm{H}}_2\mathrm{O}$
• C. $\mathrm{CaO}$
• D. ${\mathrm{MgCl}}_2$

Answer 1

The correct option is B

${\mathrm{Na}}_2{\mathrm{CO}}_3.10{\mathrm{H}}_2\mathrm{O}$

An explanation for the correct option

(B) ${\mathrm{Na}}_2{\mathrm{CO}}_3.10{\mathrm{H}}_2\mathrm{O}$

• The common name for ${\mathrm{Na}}_2{\mathrm{CO}}_3.10{\mathrm{H}}_2\mathrm{O}$ is washing soda.
• A phenomenon where a compound loses its water of crystallization on exposure to dry air is called efflorescency. Substances showing efflorescency are called efflorescent substances.
• When hydrated Sodium carbonate $({\mathrm{Na}}_2{\mathrm{CO}}_3.10{\mathrm{H}}_2\mathrm{O})$ exposed to dry air, becomes monohydrate.
• ${\mathrm{Na}}_2{\mathrm{CO}}_3.10{\mathrm{H}}_2\mathrm{O}\stackrel{\mathrm{dry}\mathrm{air}}{\rightleftharpoons }{\mathrm{Na}}_2{\mathrm{CO}}_3.{\mathrm{H}}_2\mathrm{O}+9{\mathrm{H}}_2\mathrm{O}$

(A) $\mathrm{NaOH}$

• Chemical name $\left(\mathrm{NaOH}\right)$ - Sodium hydroxide.
• A phenomenon where a compound loses its water of crystallization on exposure to dry air is called efflorescency. Substances showing efflorescency are called efflorescent substances.
• It is not an efflorescent substance.

(C) $\mathrm{CaO}$

• Chemical name $\left(\mathrm{CaO}\right)$ - Calcium oxide.
• A phenomenon where a compound loses its water of crystallization on exposure to dry air is called efflorescency. Substances showing efflorescency are called efflorescent substances.
• It is not an efflorescent substance.

(D) ${\mathrm{MgCl}}_2$

• Chemical name$\left({\mathrm{MgCl}}_2\right)$ - Magnesium chloride.
• A phenomenon where a compound loses its water of crystallization on exposure to dry air is called efflorescency. Substances showing efflorescency are called efflorescent substances.
• It is not an efflorescent substance.

Hence, b is the correct option as hydrated Sodium carbonate $({\mathrm{Na}}_2{\mathrm{CO}}_3.10{\mathrm{H}}_2\mathrm{O})$ is an efflorescent substance.