When water is added to compound (A) of calcium, solution of compound (B) is formed. When carbon dioxide is passed into the solution, it turns milky due to the formation of compound (C). If excess of carbon dioxide is passed into the solution milkiness disappears due to the formation of compound (D). Identify the compounds A, B, C and D. Explain why the milkiness disappears in the last step.
Compound (A) is Calcium oxide, CaO. Addition of water to CaO forms Compound (B), which is Ca(OH)2.
CaO + H2O → Ca(OH)2
When CO2 is passed through the Ca(OH)2 solution, it turns milky and forms a white precipitate which is Compound (C) which is calcium carbonate, CaCO3.
Ca(OH)2 + CO2→ CaCO3 + H2O
On passing excess of CO2, the precipitate dissolves to form calcium hydrogencarbonate, which is compound (D).
CaCO3 + CO2 + H2O → Ca(HCO3)2
The milkiness dissolves due to formation of a soluble compound calcium hydrogencarbonate.