Question

I have the same question as Chopsticks

determine the emperical formula of the compound

25.3%copper, 12.9%sulphur, 25.7% oxygen, 36.1% water

Can the answer be CuSO4(H2O)5?
or does it have to be CuSO4 x 5H2O

thanks in advance.

Answer 1

Assume you have 100 g of the stuff.

25.3gCu=.398 mol Cu
12.9gS=.401 mol S
25.7gO=1.61 mol O
36.1gwater=2.01mol water.

Normalize, by dividing by the lowest number of moles
Cu 1
S 1
O 4
water 5
Yes, you are right.

Answer 2

You may right the formula as
CuSO4(H2O)5 or CuSO4.5H2O or CuSO4*5H2O.
Most texts write it as CuSO4.5H2O BUT these boards don't let us put the decimal point in the middle of the line so we write a period (.) or an asterisk (*). Neither means TIMES. CuSO4*5H2O is read as copper II sulfate with 5 molecules of water of crystallization or as copper II sulfate pentahydrate.