The formula for
freezing point depression is: ΔTf = mkfi
Where:
kf = freezing point constant
i = Van't Hoff factor which in this case is 1
m = molality (moles of solute/kg of solvent)
ΔTf = temperature change
ΔTf is 3.93°C, the molality is the amount of solute Quinine in
the solvent cyclohexane. Moles cannot be calculated, therefore substitution of
moles with g/mm is needed.
moles is g/m, therefore molality is equal to (g/mm)/kg
Calculations:
molality =
(0.153/mm)/0.025 = 6.12/mm
3.93 = 6.12/mm(20.8)
mm = (6.12/3.93)(20.8) = 32.39 g/mol
