posted by thao nguyen .
A 2.50 g sample of a hydrate of calcium sulphate losses 0.523 g of water when heated. Determine the mass percent of water in the hydrate and the formula of the hydrate.
find the mole ratio of water to CaSO4.
divide moles water by the moles CaSO4, that is X
percent water = (mass H2O/mass sample)*100= (0.523/2.50)*100 = 20.92 which I would round to 20.9%.
To find the formula, take a 100 gram sample which provides
20.9 g H2O
100-20.9 = 79.1 g CaSO4
moles water = 20.9/18 = 1.16
moles CaSO4 = 79.1/136 = 0.582
Now find the ratio of water to 1 atom of the CaSO4. The easy way to do that is to divide 0.582 by 0.582 = 1.0000 CaSO4
Then 1.16/0.582 = ?? H2O
I believe it comes out to CaSO4 x 2H20
I think haha