Question

Vitamin K is involved in normal blood clotting. When 1.93 g of vitamin K is dissolved in 25.0 g of camphor, the freezing point of the solution is lowered by 6.47 °C. The freezing point and Kf constant for camphor can be found here. Calculate the molar mass of vitamin K.

Answer 1

Solution :-

Freezing point of camphor = 179.8 °C

Kf of camphor = 40.0 C/m

Change in freezing point = 6.47 C

Mass of vitamin K = 1.93 g

Mass of camphor = 25.0 g = 0.025 kg

Lets first calculate the molality of the solution

Delta Tf = Kf* m

6.47 C = 40.0 C/m * m

6.47 C / 40.0 C per m = m

0.16175 m = m

Now using the molality and kg solvent lets calculate the moles of vitamin K

Moles = molality * kg solvent

            = 0.16175 mol per kg * 0.025 kg

         = 0.00404375 mol Vit K

Now lets calculate the molar mass of vitamin K

Molar mass= mass/moles

                    = 1.93 g / 0.00404375 mol

                    = 477.3 g/mol

So the molar mass of Vitamin K is 477.3 g/mol