The normal freeing point of cyclohexane if 6.6 degrees Celsius. A 0.2g sample of an unknown solute is dissolved in 50 ml of cyclohexane (d-0.8g/ml, Kf=20 degreesCelsius/m. If the freezing point of the solution is 3.6 degrees Celsius, what is the molar mass of the solute?

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  1. delta T = Kf*molality
    Solve for molality.

    molality = moles/kg solvent. Use the density to convert 50 mL solvent to mass.
    Solve molality equation for moles.

    moles = grams/molar mass. You have moles and grams, solve for molar mass.

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  2. what grams do i use to solve for "moles = grams/molar mass?

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  3. It's the mass of the unknown that you want to determine the molar mass of. That is 0.2 g sample from the problem.

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