Ca (OH) 2 when carbon dioxide is passed through the milk of lime, an insoluble salt is formed …

Lime milk or slaked lime or “fluff” – a suspension of calcium hydroxide in water. When carbon dioxide is passed through the milk of lime, a water-insoluble salt is formed: calcium carbonate, which leads to the turbidity of the initial suspension.

Ca (OH) 2 + CO2 = CaCO3 + H2O.

This is a qualitative response to carbon dioxide. If you continue to feed carbon dioxide into the suspension, the reaction will continue and the water-insoluble calcium carbonate is converted into a water-soluble calcium bicarbonate salt and the solution becomes transparent:

CaCO3 + CO2 + H2O = Ca (HCO3) 2.