Question

Two salts 'X' and 'Y' are dissolved in water separately. When phenolphthalein is added to these two solutions, the solution 'X' turns pink and the solution 'Y' does not show any change in colour, therefore 'X' and 'Y' are:

Options

• (X) - $$\mathrm{Na}{\phantom{A}}_2\mathrm{CO}{\phantom{A}}_3$$; (Y) - $$\mathrm{NH}{\phantom{A}}_4\mathrm{Cl}$$

• (X) - $$\mathrm{Na}{\phantom{A}}_2\mathrm{SO}{\phantom{A}}_4$$; (Y) - $$\mathrm{NaHCO}{\phantom{A}}_3$$

• (X) - $$\mathrm{NH}{\phantom{A}}_4\mathrm{Cl}$$ ; (Y) - $$\mathrm{Na}{\phantom{A}}_2\mathrm{SO}{\phantom{A}}_4$$

• (x) - $$\mathrm{NaNO}{\phantom{A}}_3$$ ; (Y) - $$\mathrm{Na}{\phantom{A}}_2\mathrm{SO}{\phantom{A}}_4$$

Answer 1

(X) - $$\mathrm{Na}{\phantom{A}}_2\mathrm{CO}{\phantom{A}}_3$$; (Y) - $$\mathrm{NH}{\phantom{A}}_4\mathrm{Cl}$$

Explanation:

An indicator, phenolphthalein is a substance that changes colour when it interacts with an acid or a base. It will be pink in basic solutions and clear in acidic ones. When phenolphthalein is added, X turns pink, indicating that it is basic in nature, whereas Y does not change colour, indicating that it is acidic in nature.

The reaction of sodium hydroxide (strong base) and carbonic acid (weak acid) produces sodium carbonate. As a result, it is basic in nature.

The salt of a strong acid, hydrochloric acid (HCI), and a weak base, ammonium hydroxide $$(\mathrm{NH}{\phantom{A}}_4\mathrm{OH})$$, is ammonium chloride $$(\mathrm{NH}{\phantom{A}}_4\mathrm{Cl})$$. As a result, an ammonium chloride aqueous solution is acidic in nature.