68.0g of solute were dissolved in 393 mL of benzene. The solution froze at -0.50°C. The normal freezing point of benzene is 5.5°C and the molar freezing point constant is 5.12°C kg/mol. The density of benzene is .879 g/mol. Calculate the molar mass of the solute.

Answer 1

delta T = Kf*m. You know delta T (normal freezing point - new freezing point) and Kf, solve for m = molality.

m = mols/Kg solvent. You know m and kg solvent (use density for kg solvent; i.e., mass = volume x density). solve for mols.

mols = grams/molar mass. You know mols and grams, calculate molar mass.