Question

Menthol is a crystalline substance with a peppermint taste and odor. When 0.533 g of menthol is dissolved in 25.0 g of cyclohexane, the freezing point of the solution is lowered by 2.84 ∘C. Look up the freezing point and f constant for cyclohexane in the Colligative Constants table. Calculate the molar mass of menthol.

Answer 1

Answer: The molar mass of menthol is 156.15 g/mol

Step-by-step explanation:

Depression in freezing point is given by:

`\Delta T_f=K_f* m`

`\Delta T_f=T_f^0-T_f=2.84^0C` = Depression in freezing point

`K_f` = freezing point constant =
`20.8^0C/m`

m= molality

`\Delta T_f=K_f* \frac{\text{mass of solute}}{\text{molar mass of solute}* \text{weight of solvent in kg}}`

Weight of solvent (cyclohexane)= 25.0 g = 0.025 kg

Molar mass of solute (menthol) = ?

Mass of solute (menthol) = 0.533 g

`2.84^0C=20.8* (0.533)/(xg/mol* 0.025)`

`x=156.15g/mol`

The molar mass of menthol is 156.15 g/mol