Answer:
The molar mass of the unknown substance is 255g/mole
Explanation:
Freezing point depression is given by
ΔT = i · Kf · m
Where
m = molality of the solute
i = van't Hoff's factor = i for non electrolyte
Kf = 20.4 °C/m = cryoscopic constant
ΔT = Freezing point depression
Therefore ΔT = 6.6 - 5 = 1.6 °C
1.6 °C = 20.4 °C/m × 1 × m
Therefore m = 1.6/20.4 = 0.0784 m
number of moles in 2.50 g of cyclohexane = 0.0784 m or 0.0784 moles of the substance in 1000 grams of cyclohexane. That is
2.5 ×0.0784/1000 moles in 2.5 graams of cyclohexane that is
1.96 × 10⁻⁵ moles in 2.5 grams of cyclohexane
1.96 × 10⁻⁵ moles of the substance weighs 0.050 grams
Therefore 1 Mole weighs (0.05 g)/(1.96 × 10⁻⁵ moles) = 255g/mole
