A hydrate of magnesium sulfate, MgSO₄·nH₂O, loses 37.4% of its mass upon heating. The mass loss can be considered to be only water. What is the value of n if all of the water was lost?

Question

Quizplus · Accepted Answer

The formula of the hydrate can be simplified to MgSO4·nH2O.

Since the mass loss is only water, we can set up the following equation:

mass of water lost = (initial mass of hydrate) - (mass of anhydrous salt)

Let's assume we start with 100g of the hydrate.

mass of water lost = (100g) - (final mass after heating)

We know that the final mass after heating is 62.6g (since 37.4% of the mass was lost).

mass of water lost = (100g) - (62.6g) 
mass of water lost = 37.4g

We also know that the mass of water lost is equal to n times the molar mass of water (which is 18.015 g/mol).

So:

37.4g = n x 18.015 g/mol

n = 2.07

However, n must be a whole number, since it represents the number of water molecules in the hydrate formula. The closest whole number to 2.07 is 2.

Therefore, the value of n is 2, and the hydrate is MgSO4·2H2O.

A Hydrate of Magnesium Sulfate, MgSO4·nH2O, Loses 37

A Hydrate of Magnesium Sulfate, MgSO₄·nH₂O, Loses 37