What happens when carbon dioxide gas is bubbled through lime water: (i) In small amounts?(ii) In excess?

When carbon dioxide (CO2) gas is bubbled through lime water (calcium hydroxide solution), the following reactions occur:

(i) In small amounts of carbon dioxide:
CO2 + Ca(OH)2 -> CaCO3 + H2O

The carbon dioxide reacts with calcium hydroxide to form calcium carbonate (a white precipitate) and water. This reaction is known as a limewater test or the carbon dioxide test. The presence of the white precipitate confirms the presence of carbon dioxide.

(ii) In excess of carbon dioxide:
If carbon dioxide continues to be bubbled through the lime water in excess, the calcium carbonate formed in the previous reaction can react further with carbon dioxide:

CaCO3 + CO2 + H2O -> Ca(HCO3)2

This reaction produces calcium bicarbonate (dissolved in water). Calcium bicarbonate is soluble in water and does not form a precipitate.

So, when carbon dioxide is bubbled through lime water in excess, the solution becomes cloudy due to the formation of the calcium carbonate precipitate initially. However, as more carbon dioxide is added, the precipitate dissolves, and the solution becomes clear again due to the formation of soluble calcium bicarbonate.