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.
• Precipitated 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, , 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.