Question

Which salt solution among the following will change the colour of blue litmus paper to red?

[1 mark]

• A. NaCl
• B. ${NH}_{4}Cl$
• C. KCl
• D. ${CH}_{3}COONa$

Answer 1

The correct option is B ${NH}_{4}Cl$

The blue litmus turns red in acidic solution.

• NaCl and KCl are neutral salts which are formed by the reaction of a strong acid with a strong base. Their aqueous solutions give a neutral salt solution. Thus, we observe no change in the colour of the litmus paper when it is dipped in these salt solutions.
• ${CH}_{3}COONa$ is a basic salt because it is formed by the reaction of a strong base (NaOH) and weak acid $({CH}_{3}COOH$). So, it changes the colour of red litmus paper to blue.
• ${NH}_{4}Cl$ is an acidic salt because it is formed by the reaction of a strong acid (HCl) and weak base $\left(N{H}_{4}OH\right)$. So, it changes the colour of blue litmus paper to red.