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 is 5.144^$\circ$C. Pure benzene freezes at 5.444^$\circ$C and has a K_f of 5.12^$\circ$C/m. What is the molar mass of thyroxine A) 777 g/mol B) 787 g/mol C) 797 g/mol D) 807 g/mol E) None of the above

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Quizplus · Accepted Answer

The molar mass of thyroxine can be calculated using the formula ΔTf = Kf * m, where ΔTf is the freezing point depression, Kf is the cryoscopic constant of the solvent (benzene in this case), and m is the molality of the solution. The freezing point depression ΔTf is the difference between the freezing point of pure benzene (5.444°C) and the freezing point of the solution (5.144°C), which is 0.3°C. The molality m can be calculated as moles of solute per kilogram of solvent. Rearranging the formula to solve for the molar mass (M) of thyroxine gives M = (mass of thyroxine / (ΔTf / Kf)) / mass of solvent in kg. Substituting the given values and solving for M yields a molar mass of approximately 777 g/mol.

Thyroxine, an Important Hormone That Controls the Rate of Metabolism ∘\circ∘

Thyroxine, an Important Hormone That Controls the Rate of Metabolism $\circ$