Question

Epsom salts, a strong laxative used in veterinary medicine, is a hydrate, which means that a certain number of water molecules are included in the solid structure. The formula for Epsom salts can be written as MgSO4 · x H2O, where x indicates the number of moles of H2O per mole of MgSO4. When 5.469 g of this hydrate is heated to 250°C, all the water of hydration is lost, leaving 2.671 g of MgSO4. What is the value of x?

Answer 1

5.469 g = mass MgSO4 + xH2O
-2.671 g = mass MgSO4
--------------
2.798 g = mass H2O

mols MgSO4 = 2.671/molar mass = ?
mols H2O = 2.798/molar mass H2O = ?

Now find the ratio for 1 mol MgSO4. The easy way to do that is to divide mols MgSO4 by itself (which automatically gives you 1.00), then divide the mols H2O by the same value to find x.
Post your work if you run into trouble.

Answer 2

0.1428