Question
What happens when $CO _2$ gas is passed through lime water?
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Answer
When carbon dioxide is passed through lime water for a short time, it turns lime water milky due to formation of a white precipitate of calcium carbonate. The reaction is-$\text{Ca(OH)}_2+\text{CO}_2\rightarrow\text{CaCO}_3\downarrow+\text{H}_2\text{O}\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ (\text{white precipate})$
When carbon dioxide gas is passed through lime water for a considerable time ,then the white precipitate of calcium carbonate which is fomed initially as shown in the above reaction ,dissolves due to formation of a soluble salt calcium hydrogen carbonate and the solution becomes clear again. The reaction is-$\text{CaCO}_3\downarrow+\text{H}_2\text{O}+\text{CO}_2\rightarrow\text{Ca(HCO}_3)_2\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ {(\text{soluble in water)}}$
When carbon dioxide gas is passed through lime water for a considerable time ,then the white precipitate of calcium carbonate which is fomed initially as shown in the above reaction ,dissolves due to formation of a soluble salt calcium hydrogen carbonate and the solution becomes clear again. The reaction is-$\text{CaCO}_3\downarrow+\text{H}_2\text{O}+\text{CO}_2\rightarrow\text{Ca(HCO}_3)_2\\\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ {(\text{soluble in water)}}$
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