A solution was prepared by mixing 2.17 g of unknown non-electrolyte with 225.0 g of chloroform. The freezing point of the resulting solution is -64.2 C. The freezing point of pure chloroform is -63.5 C, and it's k(f) = 4.68 C. What is the molecular mass of the unknown.

I keep getting 64.2 g/mol but the answer in the book is 69.3 g/mol

∆°

∆

∆Tf= -63.5° - (-64.2°) = 0.70 °

m= .70°/4.68 ° (m^-1) = 0.150 m

mol solute = .150 m x (225.0 x 10^-3) kg = 33.8 x 10^-3 mol

molecular weight = 2.17 g X / (33.8 x 10^-3) = 64.2 g/mol

What is going on???

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