Calcium Carbonate and Calcium Sulphate(Plaster of Paris) - Practice Questions & MCQ

Calcium Carbonate, CaCO3
In nature, it occurs as limestone, ice land spar, marble and shells of sea animals.

Preparation
In the laboratory it is prepared by passing CO₂ through lime water or by adding sodium carbonate solution into calcium chloride as follows:

Uses

• It is used in the preparation of cement, washing soda (NaHCO₃ by Solvay method).
• In the extraction of many metals like iron.
• Marble is used as a building material.
• Precipitarcd chalk is used in the manufacture of paints, medicines and toothpaste etc.

Calcium Sulphate (Plaster of Paris), CaSO4·1⁄2 H2O
It is known as calcium sulphate hemihydrate

Preparation
It is obtained when gypsum, CaSO4·2H2O, is heated to 393 K.

Above 393 K, no water of crystallisation is left and anhydrous calcium sulphate, CaSO4 is formed. This is known as ‘dead burnt plaster’. It has a remarkable property of setting with water. On mixing with an adequate quantity of water it forms a plastic mass that gets into a hard solid in 5 to 15 minutes.

Uses

• Plaster of Paris is used for plaster of broken bones, making statues, toys, chalks etc.
• It is also used as a building material.
• It is used for making moulds for casting.