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 0.950 g of quinine is dissolved in 25.0 g of cyclohexane, the freezing point of the solution is lowered by 2.44 ∘ C. freezing point and K f constant for cyclohexane is 20.8

Answer 1

Given : decrease in freezing point = 2.44 ^oC

molality of quinine = (decrease in freezing point) / (K_f)

molality of quinine = (2.44 ^oC) / (20.8 ^oC/m)

molality of quinine = 0.117 m

mass of cyclohexane = 25.0 g = 0.0250 kg

moles of quinine = (molality of quinine) * (mass of cyclohexane in kg)

moles of quinine = (0.117 m) * (0.0250 kg)

moles of quinine = 2.93 x 10^-3 mol

molar mass of quinine = (mass of quinine) / (moles of quinine)

molar mass of quinine = (0.950 g) / (2.93 x 10^-3 mol)

molar mass of quinine = 323.9 g/mol