Question

Chemical A is used for softening of water to remove temporary hardness. A reacts with sodium carbonates to produce caustic soda. When ${CO}_2$ is bubbled through 'A' it turns cloudy. Chemically 'A' is :

• A. $CaO$
• B. ${CaCO}_3$
• C. ${Ca\left({HCO}_3\right)}_2$
• D. ${Ca\left(OH\right)}_2$

Answer 1

The correct option is D ${Ca\left(OH\right)}_2$

The chemical A is calcium hydroxide ${Ca\left(OH\right)}_2$.
It reacts with sodium carbonate to produce sodium hydroxide (caustic soda).
${Ca\left(OH\right)}_2+N{a}_{2}C{O}_3\to CaC{O}_3+2NaOH$
Calcium hydroxide reacts with carbon dioxide to form calcium carbonate. Hence, it turns milky.
${Ca\left(OH\right)}_2+C{O}_2\to CaC{O}_3\downarrow +H_{2}O$