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delta T = Kf*molality
Plug in 5.00 C for delta T, 1.86 for Kf and calculate molality.
Then molality x kg solvent x molar mass = grams.
You know molality, kg solvent, and molar mass. Calculate grams.

molar mass? where did u got the molar mass from ?

  • chem -

    You want grams, don't you?
    The formula I have came from this.
    molality = mols/kg solvent. Solve for mols.
    mols = molality x kg solvent.

    mols also = grams/molar mass
    so we set mols = mols

    so molality x kg solvent = g/molar mass
    multiply both sides by molar mass an we have
    molality x kg solvent x molar mass = grams.
    You didn't copy your question but it was something with an OH on/in it. That's what you want the molar mass of. I think I remember the question as being determine the mass of the material to make the freezing point decrease to -5.00 C.

  • chem -

    That's ethylene glycol

  • chem -

    No. I went back and reread the problem. It asks for mols, not grams.
    so molality = mols/kg solvent and this can be rearranged to
    molality x kg solvent = mols
    You know m and you know kg solvent. Solve for mols.

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