Question

Which one of the following salts on dissolution in water will give a solution of pH less than 7 at 298 K?

• A. $\text{KCN}$
• B. ${\text{CH}}_3\text{COONa}$
• C. $\text{NaBr}$
• D. ${\text{NH}}_4\text{Cl}$

Answer 1

The correct option is D ${\text{NH}}_4\text{Cl}$

The table given below shows the information regarding the constituents of salts given as the options $$\begin{array}{ccccc}\text{Salt}& \text{Acid used}& \text{Base used}& \text{Type of combination}& \text{pH of salt}\\ \text{KCN}& \text{HCN}& \text{KOH}& \text{Weak acid+Strong base}& >7\\ {\text{CH}}_3\text{COONa}& {\text{CH}}_3\text{COOH}& \text{NaOH}& \text{Weak acid+Strong base}& >7\\ \text{NaBr}& \text{HBr}& \text{NaOH}& \text{Strong acid+Strong base}& =7\\ {\text{NH}}_4\text{Cl}& \text{HCl}& {\text{NH}}_4\text{OH}& \text{Strong acid+Weak base}& <7\end{array}$$From the table given above, it can be concluded that ammonium chloride $\left({\text{NH}}_4\text{Cl}\right)$ is the salt which will give a pH less than 7 in its aqueous solution.