Builders and dentists must store plaster of Paris,

CaSO4 x 1/2 H2O, in airtight containers to prevent it from

absorbing water vapor from the air and changing to

gypsum, CaSO4 x 2H2O How many liters of water

vapor evolve when 2.00 kg of gypsum are heated at

110°C to produce plaster of Paris? At 110°C, the

density of water vapor is 0.574 g/L.

547 L of water vapour

Explanation:

Equation of reaction: 2[CaSO4.2H20] + Heat - --> 2[CaSO4.½H2O] + 3H20

From the equation of reaction above, 2 moles of gypsum when heated produces 2 moles of plaster of Paris and 3 moles of water vapour.

Molar mass of gypsum = 172 g/mol

Molar mass of H2O = 18 g/mol

Therefore, 2 * 172 g of gypsum produces 3 * 18 g of water vapour

i. e. 344 g of gypsum produces 54 g of H2O

2 Kg (2000 g) of gypsum will produce (54 * 2000) / 344 g of water vapour = 313.95 of water vapour.

Volume of water vapour produced = mass/density

Volume of water vapour = 313.95 g / 0.574 g/L = 547 L of water vapour

Therefore 547 L of water vapour are produced