Give the chemical name and formula of Plaster of Paris.
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Solution and Explanation
Chemical Name and Formula of Plaster of Paris:
The chemical name of Plaster of Paris is Calcium Sulphate Hemihydrate.
Its chemical formula is:
CaSO4 · 1/2 H2O
Detailed Explanation:
Plaster of Paris is prepared by heating gypsum (CaSO4 · 2H2O) at about 100°C to 120°C. During this process, gypsum loses three-fourths of its water of crystallization and forms calcium sulphate hemihydrate.
Chemical Equation for Preparation:
CaSO4 · 2H2O (s) → CaSO4 · 1/2 H2O (s) + 3/2 H2O (g)
The word “hemi” means half, indicating that one molecule of water is associated with two molecules of calcium sulphate.
Important Property:
When Plaster of Paris is mixed with water, it forms a paste that hardens after some time by converting back into gypsum.
Setting Reaction:
CaSO4 · 1/2 H2O + 3/2 H2O → CaSO4 · 2H2O
Conclusion:
Therefore, the chemical name of Plaster of Paris is Calcium Sulphate Hemihydrate and its chemical formula is CaSO4 · 1/2 H2O.
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