Benzene (C6H6) has a normal freezing point of 5.50oC and a density of 0.88 g/mL. When 1.28 g of naphthalene (C10H8) is dissolved in 125 mL of benzene, the freezing point of the solution is 5.03oC. Determine the molal freezing point constant for this solvent.

Answer 1

mass = density*volume
mass benzene = 0.88 g/mL x 125 mL = ?

delta T = Kf*m
You know delta T.
m = mols/kg solvent;
mols naph = 1.28/molar mass naphthalene
kg solvent = ? g benzene/1000
Solve for Kf