Question

Why does limewater turn milky when carbon dioxide gas is passed through it?

• A. Due to the formation of calcium carbonate
• B. Due to the formation of calcium hydroxide
• C. Due to the release of hydrogen gas
• D. Due to the reaction of calcium hydroxide with hydrogen gas

Answer 1

The correct option is A Due to the formation of calcium carbonate

Limewater is calcium hydroxide solution [${\text{Ca(OH)}}_2$], which is basic in nature. Carbon dioxide (${\text{CO}}_2$), being a non-metallic oxide (acidic in nature), reacts with the calcium hydroxide to form calcium carbonate (${\text{CaCO}}_3$). The reaction involved is given below:

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

Calcium carbonate obtained is white and insoluble in water, hence it makes limewater appear milky.