How much does 269 mmol of magnesium sulfate heptahydrate weigh, in grams?

66,3 g of MgSO₄· 7 H₂O

Explanation:

Some salts must be hydrated to increase solubility.

Magnesium sulfate heptahydrate has as molecular formula

MgSO₄· 7 H₂O

The molecular weight is the sum of atomic weights. Thus:

1 Mg × (24,305 g/mol) = 24,305 g/mol

1 S × (32,065 g/mol) = 32,065 g/mol

11 O × (15,999 g/mol) = 175,989 g/mol

14 H × (1,008 g/mol) = 14,112 g/mol

Molecular weight: 246,471 g/mol

269 mmol are 0,269 mol (m is mili: 1×10⁻³. It means 269×10⁻³ = 0,269)

0,269 mol of MgSO₄· 7 H₂O × (246,471 g / mol) = 66,3 g of MgSO₄· 7 H₂O

I hope it helps!