Question

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?

Answer 1

Hydrate of magnesium sulphate undergoes dehydration upon action of heat. This process can be chemically represent as follows:

MgSO4.XH2O → MgSO4 + XH20
(5.018 g) (2.449 g) (2.569 g)

Number of moles of H2O evolved =
`(2.569)/(Molecular.weight)`
=
`(2.569)/(18)`
= 0.1427
Number of moles of MgSO4 generated after decomposition,
=
`(2.449)/(Molecular.weight)`
=
`(2.449)/(120.37)`
=0.0203

Now dividing both these numbers by the smallest one to get the mole ratio that exists between MgSO4 and H20

For H2O,
`(0.1427)/(0.0203)` = 7.02 ~7

Thus, formula of hydrate is MgSO4.7H2O