HELP PLEASE! I need to find the molar mass!

Question

Quinine is a natural product extracted from the bark of the cinchona tree, which is native to South America. Quinine is used as an antimalarial agent.

When 1.62 g of quinine is dissolved in 25.0 g of cyclohexane, the freezing point of the solution is lowered by 4.17 ∘C. Look up the freezing point and 𝐾f constant for cyclohexane in the Colligative Constants table. 

Calculate the molar mass of quinine.

Answer 1

From the table provided:

Kf (freezing point constant) for cyclohexane = 20.8 ºC/m

The formula for freezing point depression is ...

∆T = imK

∆T = change in freezing point = 4.17 ºC

i = van't Hoff Factor = 1 for a non electrolyte which quinine is.

m = molality = moles quinine/kg of cyclohexane = ?

K = 20.8 ºC/m

Solving for m, we have ...

m = ∆T/(i)(K) = 4.17/(1)(20.8) = 0.200 m

This means 2.00 moles quinine/kg cyclhexane. Since there are only 0.025 kg (25 g) cyclohexane, we have..

2.00 mol/kg x 0.025 kg = 0.0050 mol

Molar mass = g/mol = 1.62 g/0.0050 mol

molar mass = 324 g/mol