chemistry
posted by thao nguyen on .
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.

CaSO4.XH2O
find the mole ratio of water to CaSO4.
moleswater=.523/18
molesCaSO4=(2.5.523)/molmassCaSO4
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
10020.9 = 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
20.9%
2:1 ratio
I think haha