Thyroxine, an important hormone that controls the rate of metabolism in the body

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 5.144degreeC. Pure benzene freezes at 5.444degreeC and has n value for the molal freezing point depression constant of K, of 5.12degreeC/m. What is the approximate molar mass of thyroxine? 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 ot benzene, the freezing point of the solution could be measured as 5.144degreeC. Pure benzene freezes at 5.444degreeC and has n value for the molal freezing point depression constant of K, of 5.12degreeC/m. What is the approximate molar mass of thyroxine?

Explanation / Answer

DeltaTf = Kf x molality

To-Ts = Kf x m

m = (5.444-5.144) / 5.12

m = 0.058

molality = (wt./Mwt) x1000/weight of solvent

Mwt = (wt/m) x 1000 / wt of solvent

       = (0.455/0.058 ) x 1000/10

        = 784.48 g

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