Calcium Hydroxide

Preparation. Calcium hydroxide is prepared simply by adding water to quick lime, CaO.

Properties. It is a white powder, only sparingly soluble in water. Its aqueous solution is known as lime water, while a suspension of slaked lime in water is known as milk of lime.

When carbon dioxide is passed through lime water, the solution turns milky as calcium carbonate is formed: Ca(OH)₂ + CO₂ → CaCO₃ + H₂O. If excess carbon dioxide is passed through instead, the milky precipitate re-dissolves, forming soluble calcium hydrogen carbonate: CaCO₃ + CO₂ + H₂O → Ca(HCO₃)₂.

Milk of lime also reacts with chlorine to give a hypochlorite, the constituent responsible for bleaching powder: 2Ca(OH)₂ + 2Cl₂ → CaCl₂ + Ca(OCl)₂ + 2H₂O. …