What happens when $$CO_2$$ is passed through lime water
(i) for short duration
(ii) for a long duration?
(i) When $$CO_2$$ is passed through lime water for a short duration, it turns lime water milky due to the formation of a white precipitate of calcium carbonate.
$$Ca(OH)_2 + CO_2 \rightarrow CaCO_3 + H_2O$$
(White ppt)
(ii) When excess of carbon dioxide gas is passed through lime water then the white precipitate calcium carbonate formed first dissolves due to the formation of a soluble salt calcium hydrogen carbonate $$Ca(HCO_3)_2$$, and the solution becomes clear again.
$$CaCO_3 + CO_2 + H_2O \rightarrow Ca(HCO_3)_2$$ (Soluble)