Question

Assertion: Sodium hydrogen-carbonate is an acidic salt.

Reason: The pH of an aqueous solution of Sodium Hydrogen-carbonate is more than 7.0.

• A. Assertion is true and the reason is false.
• B. Assertion is false and the reason is true.
• C. Both Assertion and Reason are true. The reason is the correct explanation of assertion.
• D. Both Assertion and Reason are true. The reason is not the correct explanation of assertion.

Answer 1

The correct option is B

Assertion is false and the reason is true.

Explanation for Correct Option

Assertion:-

• We know that substances which produce ${\mathrm{H}}^{+}$ions when dissolved in water are acidic and substances that produce ${\mathrm{OH}}^{-}$ions when dissolved in water are basic.
• Here we can see that when Sodium hydrogen carbonate$\left({\mathrm{NaHCO}}_3\right)$ dissociates it produces Sodium hydroxide and Carbonic acid:

$\underset{\mathrm{Sodium}\mathrm{hydrogen}\mathrm{carbonate}}{{\mathrm{NaHCO}}_3\left(\mathrm{aq}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}\underset{\mathrm{Sodium}\mathrm{hydroxide}}{\to \mathrm{NaOH}\left(\mathrm{aq}\right)(\mathrm{strong}\mathrm{base})}+\underset{\mathrm{Carbonic}\mathrm{acid}}{{\mathrm{H}}_2{\mathrm{CO}}_3\left(\mathrm{aq}\right)(\mathrm{weak}\mathrm{acid})}$

• As we know that Sodium hydroxide is a strong base, thus the solution formed after dissociation will be basic.
• Hence, sodium hydrogen carbonate$\left({\mathrm{NaHCO}}_3\right)$ is a basic salt.
• Therefore, the assertion is false.

Explanation for reason:-

• When Sodium hydrogen carbonate$\left({\mathrm{NaHCO}}_3\right)$ dissociates it produces Sodium hydroxide and Carbonic acid:

$\underset{\mathrm{Sodium}\mathrm{hydrogen}\mathrm{carbonate}}{{\mathrm{NaHCO}}_3\left(\mathrm{aq}\right)}+\underset{\mathrm{Water}}{{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)}\underset{\mathrm{Sodium}\mathrm{hydroxide}}{\to \mathrm{NaOH}\left(\mathrm{aq}\right)(\mathrm{strong}\mathrm{base})}+\underset{\mathrm{Carbonic}\mathrm{acid}}{{\mathrm{H}}_2{\mathrm{CO}}_3\left(\mathrm{aq}\right)(\mathrm{weak}\mathrm{acid})}$

• As we know that Sodium hydroxide is a strong base, and hence the solution formed after dissociation will be basic.
• We also know that the pH of Sodium hydrogen carbonate is $8.3$ which is more than 7 is thus a basic salt.
• Therefore, the reason is true.

Therefore, option (B) Assertion is false and the reason is true is the correct answer.