Question

Which of the following is a weak base

• A. $\mathrm{KOH}$
• B. $\mathrm{NaOH}$
• C. $\mathrm{Ca}{\left(\mathrm{OH}\right)}_2$
• D. ${\mathrm{NH}}_4\mathrm{OH}$

Answer 1

The correct option is D

${\mathrm{NH}}_4\mathrm{OH}$

Explanation for correct option:

D. ${\mathrm{NH}}_4\mathrm{OH}$

Bases

• Bases, according to Arrhenius's theory, are species that dissociate in water to produce hydroxyl ions ${\mathrm{OH}}^{-}$.
• According to Brönsted-Lowry theory, a base is a substance that can take a hydrogen ion, ${\mathrm{H}}^{+}$.
• Bases can be classified into two categories:

1. Strong base
2. Weak base

Strong base:

• A base that dissociates in water completely producing hydroxyl ions ${\mathrm{OH}}^{-}$ is called a strong base.
• Examples of strong bases are Sodium hydroxide$\left(\mathrm{NaOH}\right)$ as well as Potassium hydroxide $\left(\mathrm{KOH}\right)$.

Weak base:

• A base that dissociates partially in water producing hydroxyl ions ${\mathrm{OH}}^{-}$is a weak base.
• Examples of weak bases are Sodium bicarbonate$\left({\mathrm{NaHCO}}_3\right)$ as well as Ammonium hydroxide $\left({\mathrm{NH}}_4\mathrm{OH}\right)$.

Explanation for incorrect options

(A)$\mathrm{KOH}$

$\mathrm{KOH}$ is the strong base. Because it completely dissociates in an aqueous solution to give${\mathrm{OH}}^{-}$ ion .So, it is a strong base.

(B)$\mathrm{NaOH}$

$\mathrm{NaOH}$ is the strong base. Because it completely dissociates in an aqueous solution to give${\mathrm{OH}}^{-}$ ion .So, it is a strong base.

(C)$\mathrm{Ca}{\left(\mathrm{OH}\right)}_2$

$\mathrm{Ca}{\left(\mathrm{OH}\right)}_2$is the strong base. Because it completely dissociates in an aqueous solution to give${\mathrm{OH}}^{-}$ ion .So, it is a strong base.

Since ammonium hydroxide is a weak base. Thus all the options A, B, and D stand incorrect.

Hence, the correct option is D i.e. ${\mathrm{NH}}_4\mathrm{OH}$ is a weak base.