Question

Identify the compounds which on reacting with sulphuric acid produces a gas that turns limewater milky.

• A. Copper carbonate
• B. Potassium bicarbonate
• C. Sodium hydrogen carbonate
• D. Sodium hydroxide

Answer 1

Answer: (A), (B), (C)

Sodium hydrogen carbonate

Acids on reaction with metal carbonates or bicarbonates release carbon dioxide. Bicarbonates are also known as hydrogen carbonates. For example:

${\text{CuCO}}_3\text{(s)}+{\text{H}}_2{\text{SO}}_4\text{(aq)}\to {\text{CuSO}}_4\text{(aq)}+{\text{CO}}_2\text{(g)}+{\text{H}}_2\text{O}\text{(l)}$
$2{\text{KHCO}}_3\text{(s)}+{\text{H}}_2{\text{SO}}_4\text{(aq)}\to {\text{K}}_2{\text{SO}}_4\text{(aq)}+2{\text{CO}}_2\text{(g)}+2{\text{H}}_2\text{O}\text{(l)}$
$2{\text{NaHCO}}_3\text{(s)}+{\text{H}}_2{\text{SO}}_4\text{(aq)}\to {\text{Na}}_2{\text{SO}}_4\text{(aq)}+2{\text{H}}_2\text{O}\text{(l)}+2{\text{CO}}_2\text{(g)}$

This carbon dioxide $\left({\text{CO}}_2\right)$ gas which is released turns limewater [${\text{Ca(OH)}}_2)$] milky. The reaction involved is given below:

${\text{Ca(OH)}}_2\text{(aq)}+{\text{CO}}_2\text{(g)}\to {\text{CaCO}}_3\text{(s)}+{\text{H}}_2\text{O}\text{(l)}$

The calcium carbonate formed is insoluble and appears milky.

The reaction between sodium hydroxide and sulphuric acid is a neutralisation reaction where the products obtained are salt and water.