Q-} why does milkiness disappear from limewater when excess co2 is passes through it??
When carbon dioxide gas is passed through lime water, it turns milky due to the formation of calcium carbonate which is insoluble in water.
Ca(OH)2 + CO2 → CaCO3 + H2O
However, when excess of carbon dioxide is passed through this solution, the milkyness disappears. This is due the formation of calcium bicarbonate, which is soluble in water. Thus, a clear solution is obtained.
CaCO3 + H2O + CO2 → Ca(HCO3)2