Question

What would be the mass of a bag of anhydrous magnesium sulfate, MgSO4, if it contained the same amount of magnesium as a 1.00kg bag of Epsom Salts, MgSO4 . 7H2O?

Answer 1

So I calculated the mass of MgSO4 (120.37g/mol) and the mass of 7H2O (126.14g/mol). Then I divided the mass of MgSO4 by MgSO4 . 7H20 multiplied by 100%. My answer was 95.426%. But how do I get the amount of magnesium?

Answer 2

I posted an answer but deleted it. Here is what I would do. There is a shorter way but I don't believe teachers are using gravimetric factors now--pity.
How much Mg is in the 1 kg bag of MgSO4.7H2O. That will be
1.00 kg x (1 mol/molar mass MgSO4.7H2O) x (24.30 g Mg/1 mol Mg) = g Mg in the 1.00 kg bag.

Now convert that g Mg into MgSO4 and you will have your answer.

The EASY way of doing it is
1.00 Kg x (molar mass MgSO4/molar mass MgSO4.7H2O) = ??
Try it both ways. The answer should be the same. Check my work.