Question

Two salts $A$ and $B$ are dissolved in water separately. When phenolphthalein is added to the two solutions one solution turned pink and the other solution was colourless. Identify $A$ and $B$.

• A. ${CH}_{3}COONa,{NH}_{4}Cl$
• B. ${Na}_2{SO}_4,{CH}_{3}COONa$
• C. ${NH}_{4}Cl,{Na}_2{SO}_4$
• D. $Na{NO}_3,{Na}_2{SO}_4$

Answer 1

The correct option is A ${CH}_{3}COONa,{NH}_{4}Cl$

Phenolphthalein gives pink colour in a basic $pH$ range from 8.2 to 10.
When option $\left(A\right)$ dissolved in water
${CH}_{3}COONa+H_{2}O\to {CH}_{3}COOH+NaOH$ (Strong base, Pink)
$N{H}_{4}Cl+H_{2}O\to N{H}_{4}OH+HCl$ (Strong acid, colourless)
Option $\left(B\right)$ dissolved in water
${Na}_2{SO}_4+H_{2}O\to NaOH+H_{2}S{O}_4$ (Strong acid, strong base colourless)
${CH}_{3}COONa+H_{2}O\to C{H}_{3}COOH+NaOH$(Strong base pink)
Option $\left(C\right)$ dissolved in water
${NH}_{4}Cl,{Na}_2{SO}_4$ (Both colourless)
Option $\left(D\right)$ dissolved in water
$Na{NO}_3,{Na}_2{SO}_4$(Both Colourless)
Hence, two salts $A$ and $B$ are ${CH}_{3}COONa$ and $N{H}_{4}Cl$.