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
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.
To find the mass of H2O in 80 g of epsom salt (MgSO4 x 7H2O), you need to calculate the molar mass of the compound and then determine the proportion of H2O.
1. First, calculate the molar mass of MgSO4 x 7H2O:
Molar mass of MgSO4 = 24.31 (Molar mass of Mg) + 32.06 (Molar mass of S) + (4 × 16.00) (Molar mass of O)
= 120.37 g/mol
Molar mass of H2O = 2 × 1.01 (Molar mass of H) + 16.00 (Molar mass of O)
= 18.02 g/mol
Molar mass of MgSO4 x 7H2O = (120.37 g/mol) + 7 × (18.02 g/mol)
= 246.47 g/mol
2. Next, calculate the proportion of H2O in the compound:
Proportion of H2O = (7 × molar mass of H2O) / molar mass of MgSO4 x 7H2O
= (7 × 18.02 g/mol) / 246.47 g/mol
= 0.5105
3. Finally, find the mass of H2O in 80 g of epsom salt:
Mass of H2O = Proportion of H2O × mass of epsom salt
= 0.5105 × 80 g
≈ 40.84 g
Therefore, the mass of H2O in 80 g of epsom salt is approximately 40.84 g.