Multiple choice

Plaster of Paris is also written as

  1. CaSO4

  2. CaSO4.2H2O

  3. CaSO4.1/2 H2O

  4. CaSO4.H2O
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Plaster of Paris is calcium sulfate hemihydrate, represented as CaSO4·1/2H2O, meaning each calcium sulfate unit is associated with half a water molecule. It's produced by heating gypsum (CaSO4·2H2O) to about 150°C, which drives off about 1.5 water molecules per unit. When mixed with water, it rehydrates to form gypsum, creating a hard solid - the basis for casts and molds.

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