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7 August, 17:14

How many moles of water molecules are in 6.81 g of magnesium sulfate heptahydrate (Epsom salts

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  1. 7 August, 18:53
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    Answer: 0.34 mol

    Justification:

    1) Hepta means 7, so heptahyrate means 7 parts of water. On mole of magnesium sulfate heptadydrate has seven moles of water.

    2) The formula of magnesium sulfate heptahydrate is:

    Mg SO4. 7 H2O

    3) Calcualte the number of moles of the compound by dividing the mass in grams by the molar mass of formula.

    molar mass:

    Mg: 24.3 g/mol

    S: 32.1 g/mol

    O4: 4 * 16.0 g/mol = 64.0 g/mol

    H2: 2 * 1.0 g/mol = 2.0 g/mol

    O: 16 g/mol

    Molar mass = 24.3 g/mol + 32.1 g/mol + 64.0 g/mol + 2.0 g/mol + 16.0 g/mol = 138.4 g/mol

    number of moles = mass in grams / molar mass = 6.81 g / 138.4 g/mol = 0.049 mol

    4) As stated, there are 7 moles of H2O per each mol of heptahydrate compoind, so the number of moles of water is 7 * 0.049 mol = 0.343 mol

    Answer: 0.34 mol
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