Question

Vitamin K is involved in normal blood clotting. When 0.802 g of vitamin K is dissolved in 25.0 g of camphor, the freezing point of the solution is lowered by 2.69 °C. The freezing point and Kf constant for camphor can be found here. Calculate the molar mass of vitamin K.

Answer 1

Answer:

Molar mass of vitamin K = 450.56\frac{g}{mol}[/tex]

Explanation:

The freezing point of camphor = 178.4 ⁰C

the Kf of camphor =  37.7°C/m

where : m = molality

the relation between freezing point depression and molality is

Depression in freezing point = Kf X molality

Where

Kf = cryoscopic constant of camphor

molality = moles of solute dissolved per kg of solvent.

putting values

2.69°C = 37.7°C/m X molality

molality = 0.0714 mol /kg

$molality=\frac{molesofvitaminK}{massofcamphor(kg)}=\frac{moles}{0.025}$

moles of vitamin K = 0.0714X0.025 = 0.00178 mol

we know that moles are related to mass and molar mass of a substance as:

$moles=\frac{mass}{molarmass}$

For vitamin K the mass is given = 0.802 grams

therefore molar mass = $\frac{mass}{moles}=\frac{0.802}{0.00178}=450.56\frac{g}{mol}$