Answer:
Molar mass of menthol is 155.86 g/mol
Explanation:
Let's apply the colligative property of freezing point depression:
ΔT = Kf . m . i
As menthol is an organic compound we assume the i (Van't Hoff factor as non electrolytic, so i = 1)
m = mol /kg (molality)
Kf = Cryoscopic constant, in this case, for cyclohexane
ΔT = T° freezing of pure solvent - T° freezing solution
7.90°C = 20.8°C / m . m . 1
7.90°C / 20.8 m/°C = m
0.380 m = molality
0.380 moles are the moles of solute (menthol) dissolved in 1kg of solvent, but our mass of solvent is 25 g.
Let's convert the g of solvent to kg to work with molality
25 g = 0.025 kg
molal . solvent mass = moles of solute
0.380 mol /kg . 0.025kg = 9.49×10⁻³ moles
Now, we have the moles and the mass of solute. Let's determine the molar mass of menthol (grams / moles)
1.48 g / 9.49×10⁻³ m = 155.86 g/m
