Question

If you blow into a glass of limewater, what is the change in colour you can observe?

• A. Colourless to milky-white
• B. Colourless to brown
• C. Brown to colourless
• D. Milky-white to colourless

Answer 1

The correct option is A

Colourless to milky-white

• Limewater is a diluted solution of calcium hydroxide $\left(Ca\right(OH{)}_2)$, which is colourless.
• When one blows air into a glass of limewater, the carbon dioxide gas present in the exhaled air reacts with calcium hydroxide and forms calcium carbonate.
• Calcium carbonate is insoluble in water which gives a milky appearance to the solution. The reaction for the same is given below:

$\mathrm{Ca}\left(\mathrm{OH}{)}_2\right(\mathrm{aq})+{\mathrm{CO}}_2(g)\to {\mathrm{CaCO}}_3(s)+H_{2}O(l)\mathrm{Calcium}\mathrm{Carbon}\mathrm{Calcium}\mathrm{Water}\mathrm{hydroxide}\mathrm{dioxide}\mathrm{carbonate}$