Anhydrous copper(II) sulfate??

Question

a 0.755 g sample of hydrated copper(II) sulfate

CuSO4 * xH2O

was heated carefully until it had changed completely to anhydrous copper(II) sulfate with a mass of 0.483 g. Determine the value of x.

I don't understand how to tackle this problem at all. My teacher never taught us anything on this =[ Any help is veryyy appreciated, thank you in advance.

Answer 1

The key to this kind of problem is just dig in.  Also I advise you not to expect your teacher to have taught you every possible problem that you might ever see because that is not realistic.  Eventually you have to use your knowledge and your understanding of the concepts to solve problems that you have never seen before.  

start by figuring out the mass loss ... it's all water.

0.755 g - 0.483 = 0.272

Now, the 0.483 is just CuSO4 and you can convert that to moles.

0.486 g x 1 mol / 159.6 g = 0.00305 mol of CuSO4

Now convert your water to moles

0.272 g x 1 mol / 18 g = 0.015 mol of H2O

0.015 / 0.00305 gives you the ratio = 5 mol water per mol CuSO4

So it's CuSO4 "dot" 5(H2O)