Calcium Carbonate (CaCO3)

Calcium carbonate, CaCO3, occurs naturally as chalk, limestone and marble. It can be prepared in two ways: (i) by bubbling carbon dioxide through a solution of calcium hydroxide (slaked lime), which precipitates the water-insoluble calcium carbonate, Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l) — care must be taken not to pass excess CO2, since that converts the CaCO3 precipitate into water-soluble calcium bicarbonate and redissolves it; or (ii) by mixing a solution of calcium chloride with a solution of sodium carbonate, which precipitates calcium carbonate directly, CaCl2(aq) + Na2CO3(aq) → CaCO3(s) + 2NaCl(aq).

Properties: calcium carbonate is a soft, light, white, practically water-insoluble powder. On heating to about 1200 K it decomposes into calcium oxide and carbon dioxide, CaCO3(s) →(1200 K) CaO(s) + CO2(g). It reacts readily with dilute acids to give the corresponding calcium salt plus carbon dioxide, e.g. CaCO3 + 2HCl → CaCl2 + CO2 + H2O and CaCO3 + H2SO4 → CaSO4 + CO2 + H2O. …