Question

Thyroxine, an important hormone that controls the rate of metabolism in the body, can be isolated from the thyroid gland. When 0.455 g thyroxine is dissolved in 10.0 g benzene, the freezing point of the solution is depressed by $0.300°C$ . What is the molar mass of thyroxine?

Short answer

The molar mass is 780g/mol.

Step-by-step solution

Step 1:

Freezing point depression is$\Delta T_f=i\times K_f\times m$

Calculate the molarity from thefreezing point depression.

$m=\frac{\Delta T}{K_f}=\frac{0.300°C}{5.12°Ckg/mol}=0.0586mol/kg$.

Step 2:

Calculate the moles ofthyroxinein benzene from molarity.

$n\left(reserpine\right)=5.86\times {10}^{-3}kg$

Step 3:

The molar mass is molar mass =mass(thyroxine)/n((thyroxine).

$\frac{0.455}{5.86\times {10}^{-4}mol}=780g/mol$