When 2.41 g of vitamin K is dissolved in 25.0 g of camphor, the freezing point of the solution is lowered by 8.07 ∘C.

Question

Calculate the molar mass of vitamin K.

Answer 1

∆T = imK

∆T = freezing point change = 8.07º

i = van't Hoff factor = 1 for vitamin K since it is a non electrolyte

m = molality = mols Vit K / kg camphor = ?

K = freezing constant for camphor = should be given in the question. Looked it up & it is 40ºC/m

Solving for molality (m);

m = ∆T /(i)(K)

m = 8.07 / (1)(40)

m = 0.20175 mols Vit K / kg camphor

Since we have 25.0 g camphor, we can determine moles of Vit K present:

25.0 g camphor x 1 kg / 1000 g = 0.025 kg

0.20175 mols / kg x 0.025 kg = 0.00504 mols Vit K

Since molar mass = grams / moles, we now have sufficient info to calculate molar mass:

molar mass = 2.41 g / 0.00504 mols = 478 g / mol