Epsom salt, a common hydrate, has the formula shown below. If I measure out 125 g of epsom salt to add to my foot soak, what mass of the epsom salt is H2O?

The answer to your question is 64.02 g of H₂O

Explanation:

Data

Mass of magnesium sulfate hepta hydrated = 125 g

Mass of water = ?

Process

1.- Calculate the molar mass of the salt and the molar mass of water

molar mass of MgSO₄ 7H₂O = 24 + 32 + 64 + 14 + 112 = 246 g

mass of H₂O = 2 + 16 = 18 g

2.- Use proportions to calculate the mass of water in the epsom salt

                246 g MgSO₄ 7H₂O 126 g of H₂O

                125 g                           x

                x = (125 x 126)/246

                x = 15750/246

               x = 64.02 g of H₂O