Question

Epsom salt, a common hydrate, has the formula shown below. If I measure out 80 g of epsom salt to add to my foot soak, what mass of the epsom salt is H2O? You MUST SHOW WORK for credit.

MgSO4 x 7H2O

Answer 1

molar mass MgSO4 = approx 120
molar mass H2O = 18
mass H2O in 7 moles = aprox 126
molar mass MgSO4.7H2O = approx 120 + approx 126 = approx 246
%H2O in MgSO4.7H2O = (126/246)*100 = approx 51%
Then 0.51 x 80 g you take for you soak = the amount of water.
You may want to calculate it a litle closer.