Question

Thyroxine, an important hormone that controls the rate of metabolism in the body can be isolated from the thyroid gland. If 0.455 g of thyroxine is dissolved in 10.0 g of benzene, the freezing point of the solution could be measured as 5.144°C. Pure benzene freezes at 5.444°C and has a value for the molal freezing-point-depression constant of Kf of 5.12°C/m. What is the approximate molar mass of thyroxine?

Answer 1

delta T = Kf*molality
Solve for m

m = mols/kg solvent.
Substitute and solve for mols.

mols = grams/molar mass
Substitute and solve for molar mass.