The freezing point of pure cyclohexane is 6.60°C and the freezing point depression constant is 20.00°C/m. The freezing point of a solution containing 0.161 g of an unknown nonelectrolyte solute and 5.818 g of cyclohexane was 3.98°C. What is the molar mass of the unknown nonelectrolyte solute?

Question

The freezing point of pure cyclohexane is 6.60°C and the freezing point depression constant is 20.00°C/m.   The freezing point of a solution containing 0.161 g of an unknown nonelectrolyte solute and 5.818 g of cyclohexane was 3.98°C. What is the molar mass of the unknown nonelectrolyte solute?

PsyDAG · Answer

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DrBob222 · Answer

delta T = Kf*m
Substitute delta T (6.60-3.98), Kf (20.00) and solve for m = molality

m = mols/kg solvent. You know m and kg solvent (0.005818); solve for mols

mols = grams/molar mass. You know mols and grams, solve for molar mass.