Pure Benzene, C₆H₆, Has a Freezing Point of 5

Multiple Choice

Pure benzene, C₆H₆, has a freezing point of 5.45°C. Its freezing point depressionconstant is: K_f = 5.07 °C m^-1. A solution was made by taking 24.20 g of an unknown nonelectrolyte and dissolving it in 125.0 g of benzene. The measured freezing point of the solution was -1.65°C. Calculate the molecular weight of the unknown substance.Hint: Find molality, then moles, then molar mass, being sure to keep track of units.

A) 138 g mol^-1
B) 145 g mol^-1
C) 258 g mol^-1
D) 272 g mol^-1
E) 595 g mol^-1