Finding Formula of a hydrate~Chemistry

The formula for Epsom salts can be written as MgSO4 - xH2O, where x indicates the number of H2O moles of per mole of MgSO4. When 4.555 g of this hydrate is heated to 250 degrees C, all the water of hydration is lost, leaving 2.225 g of MgSO4. What is the value of x?

The formula for Epsom salts can be written as MgSO4 - xH2O, where x indicates the number of H2O moles of per mole of MgSO4. When 4.555 g of this hydrate is heated to 250 degrees C, all the water of hydration is lost, leaving 2.225 g of MgSO4. What is the value of x?



MgSO4 * x H2O → MgSO4 + x H2O
In the balanced equation, the coefficient is the number of moles of a reactant or product.

Mass of 1 mole of MgSO4 = 24.3 + 32.1 + 64 = 120.4


The mole ratio of H2O to MgSO4 = 1 / x

4.555 g of this hydrate – 2.225 g of MgSO4 = 2.33 grams of H2O

Moles of MgSO4 = mass of MgSO4 ÷ molar mass = (2.225 ÷ 120.4) = 0.01848
Moles of H2O = (2.33 ÷ 18) = 0.1294

The mole ratio of MgSO4 to H2O = 0.01848 / 0.1294

1 / x = 0.01848 / 0.1294
x = 7.002 ≈ 7

MgSO4 * 7 H2O