CALCIUM CARBONATES
Preparation:
(1) It is prepared by passing carbondioxide through calcium hydroxide solution.
Ca(OH)2 + CO2 → CaCO3 + H2O
(2) It can also be prepared by adding ammonium carbonate to calcium chloride solution.
CaCl2 + (NH4)2 CO3 → CaCO3 + 2NH4Cl
Properties:
(1) It is white powder
(2) When carbondioxide is passed through calcium carbonate a clear solution is obtained due to the formation of calcium bicarbonate.
CaCO3 + H2O + CO2 → Ca (HCO3)2
(3) On heating till 1000ºC we get calcium oxide and carbondioxide.
CaCO3 CaO + CO2
CALCIUM SULPHATE
Preparation:
Calcium Sulphates is prepared by the action of dilute sulphuric acid over calcium chloride.
CaCl2 + H2SO4 → CaSO4 + 2HCl
Properties:
(1) It exists as white crystalline solid with two molecules of water of crystallization.
(2) When calcium sulphates is heated to 120ºC we get plaster of Paris due to the loss of 3/4 of water molecules of crystallization. However when heated to 200ºC it forms dead burnt plaster.
2CaSO4.2H2O (CaSO4)2 H2O + 3H2O
(Plaster of Paris)
(CaSO4)2 H2O 2CaSO4 + H2O
(Anhydrite)
(3) When heated with carbon it forms calcium Sulphide and carbon monoxide.
CaSO4 + 4C → CaS + 4CO
(4) It reacts with ammonia and CO2 to form ammonium Sulphate and Carbon dioxide.
CaSO4 + 2NH3 + CO2 + H2O → (NH4)2SO4 + CaCO3