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Chemical Process - Engineering

Q1:

Calcination of gypsum produces

A plaster of paris

B salt cake

C nitre cake

D lime

ANS:A - plaster of paris

Calcination of gypsum produces plaster of Paris for several reasons:

1. Chemical Process:

  • Heating Reaction: When gypsum (calcium sulfate dihydrate, CaSO₄·2H₂O) is heated to about 150-180 °C, it undergoes calcination, losing water to form calcium sulfate hemihydrate (CaSO₄·½H₂O), known as plaster of Paris.

2. Water Loss:

  • Dehydration: The process involves the removal of two water molecules from the gypsum structure, leading to a powdery form that can rehydrate easily.

3. Rehydration Properties:

  • Setting Ability: Plaster of Paris can be mixed with water to form a paste that sets quickly upon hardening, making it useful for casting molds, making sculptures, and in construction applications.

4. Versatile Applications:

  • Construction and Art: It is widely used in construction for making decorative elements, as well as in art for creating sculptures and molds due to its smooth finish and ease of use.

5. Temperature Control:

  • Controlled Calcination: The process is carefully controlled to ensure the proper formation of plaster of Paris without converting it into anhydrite (CaSO₄) by excessive heating.

Summary:

In summary, calcination of gypsum produces plaster of Paris through the dehydration of calcium sulfate dihydrate, resulting in a versatile material that sets quickly when mixed with water, widely used in construction and artistic applications.