A 5.018 gram sample of a certain hydrate of magnesium sulfate, MgSO4•xH2O, is heated until all the water is driven off. The resulting anhydrous compound weighs 2.449 grams.

What is the formula of the hydrate?

The correct answer is MgSO₄.7H₂O.

The hydrate of magnesium sulfate goes through dehydration due to action of heat. This procedure can be represented chemically as follows:

MgSO₄. XH₂O (5.018 g) = MgSO₄ (2.449 g) + XH₂O (2.569 g)

The number of moles of H2O evolved = 2.569 / molecular weight

= 2.569 / 18 = 0.1427

Number of moles of MgSO₄ produced after decomposition,

= 2.449 / molecular weight

= 2.449 / 120.37

= 0.0203

Now dividing both these numbers to obtain the mole ratio, which prevails between MgSO₄ and H₂O

For H2O = 0.1427 / 0.0203 = 7.02 or 7

Therefore, the formula for the hydrate is MgSO₄.7H₂O.