Thyroxine,an important hormone that controls the rate of metabolism in the body,can be isolated from the thyroid gland.If 0.454 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 K_f of 5.12°C/m.What is the approximate molar mass of thyroxine? A)775 g/mol B)7.75 g/mol C)7.75 × 10⁵ g/mol D)42.7 g/mol E)11.3 g/mol

Question

Quizplus · Accepted Answer

The molar mass of thyroxine can be calculated using the formula ΔTf = Kf * m, where ΔTf is the change in freezing point, Kf is the molal freezing-point-depression constant, and m is the molality of the solution. The change in freezing point (ΔTf) is 5.444°C - 5.144°C = 0.3°C. The molality (m) can be calculated as moles of solute per kilogram of solvent, and rearranging the formula gives moles of solute = (ΔTf / Kf) * kilograms of solvent. Substituting the given values, we find the moles of thyroxine, and then use the mass of thyroxine divided by its moles to find its molar mass, which is approximately 775 g/mol.

Thyroxine,an Important Hormone That Controls the Rate of Metabolism in the Body,can