Question

Give chemical name, formula and uses of Plaster of Paris.

Answer 1

Hint: Plaster of Paris is also known as Gypsum plaster and finds is widely used in making casts and moulds. It hardens into a solid structure on drying.

Complete step by step answer:
Plaster of Paris, also referred to as Gypsum plaster. It is a white dry plaster powder, which is applied as a quick setting paste with water.
Chemical name: Calcium sulphate hemihydrate
Formula: \[CaS{{O}_{4}}.\dfrac{1}{2}{{H}_{2}}O\] or \[2CaS{{O}_{4}}.{{H}_{2}}O\]

Plaster of Paris has the following applications –
1. It is used in the preparation of protective and decorative coating of walls and ceiling.
2. It is used to make structures, sculptures and metal castings.
3. It is used in dentistry to make dentures and replicas of oral tissues and teeth.
4. It is used in the medical industry in orthopedics to make casts arounds fractures bones.
5. It is also being used in 3D printing.
6. It is also used by funeral services to remake destroyed/damaged tissue and reconnect severed limbs of dead bodies.

Note: Plaster of Paris is prepared by heating gypsum at around 120 degree Celsius. The reaction is as given below –
\[CaS{{O}_{4}}.2{{H}_{2}}O\xrightarrow{heat}CaS{{O}_{4}}.\dfrac{1}{2}{{H}_{2}}O+\dfrac{1}{2}{{H}_{2}}O\]
On heating gypsum at around 120 degree Celsius, it loses water and becomes calcium sulfate hemihydrate, which is known as the plaster of Paris. Plaster of Paris re-structures into gypsum when water is mixed with its dry form. The process of hardening and setting starts around 10 minutes after blending and is completed in about 45 minutes. However, it completely sets after 70-75 hours.