Question

When carbon dioxide is passed through lime water, the lime water turns…………

Answer 1

Step 1: Understanding the concept

• Lime water undergoes a two-step reaction with carbon dioxide $\left({\mathrm{CO}}_2\right)$.
• Calcium hydroxide dissolved in water is known as limewater.

Step 2: Reaction of carbon dioxide with lime water

1. Calcium hydroxide dissociates into ions as follows:

$\mathrm{Ca}{\left(\mathrm{OH}\right)}_2+{\mathrm{H}}_2\mathrm{O}\to {\mathrm{Ca}}^{+}+2{\mathrm{OH}}^{-}$

2. ${\mathrm{Ca}}^{2+}$ reacts with ${\mathrm{CO}}_2$ to give calcium carbonate (insoluble white precipitate in water that appears milky).

$\mathrm{Ca}{\left(\mathrm{OH}\right)}_2+{\mathrm{CO}}_2\to {\mathrm{CaCO}}_3+{\mathrm{H}}_2\mathrm{O}$

Hence, when carbon dioxide is passed through lime water, the lime water turns milky.