Question

thyroxine an important hormone that controls the rate of metabolism in the body, can be isolated from the thyroid gland. When 0.455g of thyroxine is dissolved in 10.0g of benzene, the freezing point of the solution is depressed of the solution is depressed by .300*C. What is the molar mass of thyroxine?

Answer 1

Answer: Molar mass of thyroxine is 776.5 g/mol.

Explanation:

$\Delta T_f=K_f\times m$

Mass of thyroxine = 0.455 g

Mass of benzene = 10g =0.01kg   (1 kg = 1000 g)

Formula used :  

$Delta T_f=K_f\times\frac{\text{Mass of thyroxine}}{\text{Molar mass of thyroxine}\times \text{Mass of benzene in Kg}}$

where,

$\Delta T_f$ = change in freezing point = $0.300oC$

$K_f$ = freezing point constant = $5.12°Ckg/mol$

m = molality

Now put all the given values in this formula, we get

$0.300^0C=5.12^0Ckg/mol\times \frac{0.455g}}{\text{Molar mass of thyroxine}\times {0.01kg}$

${\text{Molar mass of thyroxine}}=776.5g$

Thus  molar mass of thyroxine is 776.5 g/mol.