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 2.10 g of quinine is dissolved in 25.0 g of cyclohexane, the freezing point of the solution is lowered by 5.40

Answer 1

The formula for freezing point depression is
?Tf = mkfi

kf is the freezing point constant
i is the Van't Hoff factor which in this case is 1
m is molality (moles of solute/kg of solvent)
?Tf is temperature change

?Tf is 5.40°C, the molality is the amount of solute Quinine
in the solvent cyclohexane. We cannot calculate moles therefore we need to substitute moles with g/mm.

moles = g/mm so molality=(g/mm)/kg
molality = (2.10/mm)/0.025 = 84/mm

5.4= 84/mm(20.8) rearrange

mm = (84/5.4)(20.8) = 323.5 g/mol