Pure Cyclohexane, C₆H₁₂, Has a Freezing Point of 6

Multiple Choice

Pure cyclohexane, C₆H₁₂, has a freezing point of 6.53°C. Its freezing point depression constant is: K_f = 20.0 °C m^-1. A solution was made by taking 18.55 g of an unknown nonelectrolyte and dissolving it in 150.0 g of cyclohexane. The measured freezing point of the solution was -4.28°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) 61.8 g mol^-1
B) 66.8 g mol^-1
C) 229 g mol^-1
D) 578 g mol^-1
E) 1099 g mol^-1