s-Block Elements : CALCIUM CARBONATES

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 \quad \underrightarrow { \quad 100{ 0 }^{ 0 }C\quad } 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 \quad \underrightarrow { \quad 12{ 0 }^{ 0 }C\quad }   (CaSO4)2 H2O + 3H2O

                                                                             (Plaster of Paris)

                             (CaSO4)2 H2O \quad \underrightarrow { \quad 20{ 0 }^{ 0 }C\quad }   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