Question

22. Identify the strong acid and weak base, respectively, among the following

• A. HCl and KOH
• B. Ca(OH)₂ and Al(OH)₃
• C. HNO₃ and Al(OH)₃
• D. H₂CO₃ and NH₄OH

Answer 1

The correct option is C

HNO₃ and Al(OH)₃

Explanation for correct option:

(c) HNO₃ and Al(OH)₃

$\underset{\mathrm{Nitric}\mathrm{acid}}{{\mathrm{HNO}}_3}\to \underset{\mathrm{Hydronium}\mathrm{ion}}{{\mathrm{H}}^{+}}+\underset{\mathrm{Nitrate}\mathrm{ion}}{{{\mathrm{NO}}_3}^{-}}$

Here, HNO₃ is a strong acid because it completely gets ionized to produce H⁺ ions.

$\underset{\mathrm{Aluminium}\mathrm{hydroxide}}{\mathrm{Al}{\left(\mathrm{OH}\right)}_3}\rightleftharpoons \underset{\mathrm{Aluminium}\mathrm{ion}}{{\mathrm{Al}}^{3+}}+\underset{\mathrm{Hydroxide}\mathrm{ion}}{3{\mathrm{OH}}^{-}}$

Al(OH)₃ is a weak base because it is partially ionized in water to produce OH^- in small amounts.

Explanation of incorrect options:

(a) HCl and KOH

In this HCl is strong acid because it completely gets ionized to produce H⁺ ions in an aqueous solution. KOH is a strong base as it gets ionized completely to produce OH^- ions.

(b) Ca(OH)₂ and Al(OH)₃

Both are weak bases because they are partially ionized in water to produce OH^- in small amounts.

(d) H₂CO₃ and NH₄OH

H₂CO₃ is a weak acid as it gets ionized partially to produce small amount of H⁺ ions.

NH₄OH is a weak base, it does not get ionized completely so, it produce very small amount of OH^- ions

Hence, option (C) is the correct answer.