Answer to Question #137164 in General Chemistry for Javier

Question

The compound MgSO4 is called Epsom salts. How many grams will you need to prepare a bath containing 4.60 moles of Epsom salts?

Answer 1

Actually, the compound MgSO₄ is not Epsom salt. Epsom salt is the heptahydrate : MgSO₄·7H₂O. The molar mass of the heptahydrate is 246.47 g/mol, while the molar mass of MgSO₄ is 120.37 g/mol. Therefore, if you really have Epsom salt, in order to prepare a bath containing 4.60 moles of Epsom salt, you need

$m = nM = 4.60\text{ mol}·246.47\text{ g/mol} = 1133.8$ g .

If you have anhydrous MgSO₄, you will need:

$m = nM = 4.60\text{ mol}·120.37\text{ g/mol} = 553.7$ g and water, of course.