Question

What visible change is observed in limewater (colourless) when ${\text{CO}}_2$ gas is passed through it?

• A. The solution turns blue
• B. The solution turns green
• C. The solution turns milky
• D. No colour change

Answer 1

The correct option is C The solution turns milky

• Limewater is the common name for calcium hydroxide. When ${\text{CO}}_2$ gas is passed through it, calcium carbonate is formed.
• Calcium carbonate is white in colour and insoluble in water. Hence, the solution turns milky. The reaction is:

$Ca\left(OH{)}_2\right(aq)+{CO}_2(g)\to CaC{O}_3(s)+H_{2}O$(l)