Which of the following changes occur when an excess of `CO_(2)(g)` is passed into a clear solution of limewater ?

Options

A. A white precipitate of `CaCO_(3)` is formed.
B. A white precipitate of `CaCO_(3)` is formed initially which changes into soluble `CA(HCO_(3))_(2)` on passing excess `CO_(2)` gas.
C. A white precipitate of `Ca(HCO_(3))_(2)` is formed.
D. A white precipitate of both `CaCO_(3) "and" Ca(HCO_(3))_(2)` is formed.

Answer

B

Explanation

When `CO_(2)(g)` is passed through lime water, it turns milky due to the formation of insoluble calcium carbonate:
`Ca(OH)_(2)+CO_(2)toCaCO_(3)^(-)+H_(2)O`
On passing excess of `CO_(2)(g)` the precipitate of `CaCO_(3)` dissolves to form soluble calcium bicarbonate. Hence the milkiness disappears.
`CaCO_(3)+CO_(2)+H_(2)Otounderset("soluble")(Ca(HCO_(3))_(2))`
If this clear solution of `Ca(HCO_(3))_(2)` is heated, the solution again turns milky due to te decomposition of calcium bicarbonate bakc to calcium carbonate:
`Ca(HCO_(3))_(2)overset(Delta)toCaCO_(3)darr+CO_(2)+H_(2)O`