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Math Help - Help me find Molarity

  1. #1
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    Help me find Molarity

    the molality of a solution LiF is .866m.

    if its density is 1.10g/mL, what is its molarity?

    im lost. how do i get mass, so i can find the moles, and the L of the solution?
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  2. #2
    Senior Member mollymcf2009's Avatar
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    Hello NeedHelp!

    To find the molarity given the molality and the density:

    First, since you are given the molality, let's just assume that you are working with 1 kg of water as your solvent. Use this as a conversion factor to get moles of your solute:

    molality  (m) = \frac{moles:solute}{kg:solvent}

    1) Multiply both sides by kg to get moles.

    m \cdot kg = mol_{LiF} = 0.866 mols

    2) Use Molar Mass of LiF to get grams

    0.866 mol \cdot \frac{25.99g}{1 mol} = 22.43 g

    3) g solute + g solvent = grams solution

    1000g + 22.43g = 1022.43 g

    4) Find liters

    1022.43 \cdot \frac{1 mL}{1.10g} \cdot  \frac{1 L}{1000 mL} = .93 L

    5) Use your moles from #1 & your liters from #4 to get your molarity:

    M = \frac{mol_{LiF}}{L_{soln}} = \frac{.866 mol}{.93 L} = .932 M

    Hope that helps! Good luck!
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