Homework Help: chemistry

Posted by thao nguyen on Friday, February 19, 2010 at 2:20pm.

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.

chemistry - bobpursley, Friday, February 19, 2010 at 3:37pm
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
chemistry - DrBob222, Friday, February 19, 2010 at 3:40pm
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
chemistry - Chris, Saturday, February 16, 2013 at 12:30am
I believe it comes out to CaSO4 x 2H20

20.9%

2:1 ratio

I think haha

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