Some important compounds of calcium are limestone CaCO3, quicklime CaO and slaked lime Ca(OH)2.Limestone is heated in kilns to produce quicklime by thermal decomposition.CaCO3(s) → CaO(s) + CO2(g)Lime is used to make building mortar, to neutralise acidic soils and to make glass.The reaction of calcium oxide with water produces calcium hydroxide.CaO(s) + H2O(l) → Ca(OH)2(s)Ca(OH)2(s) is called slaked lime. It is slightly soluble in water. When dissolved in water it forms Ca(OH)2(aq) or limewater. The addition of carbon dioxide to limewater makes it go cloudy as a precipitate of calcium carbonate is formed.Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l)