Question

Menthol is a crytalling substance with peppermint taste. A 6.3% solution of menthol in cyclohexane freezes at `1.9^(@)C`. Determine the molar mass of menthol. The freezing point and molal depression constant of cyclohexane are `6.5^(@)C` and 20.2 K `m^(-1)` respectively.

Answer 1

A 6.2 p-ercent solution of menthol means that 6.2 g of the colute are dessolved in 100 g of the solution. Therefore mass of solvent is 93.8g.
`M_(B)-(K_(f)xxW_(B))/(DeltaT_(f)xxW_(A))`
`W_(B)=6.2g, W_(A)=93.8 g=0.0938 kg,`
`DeltaT_(f)=1.95-(-6.5)=8.45 K, K_(f)=20.2 K kg mol^(-1)`
`M_(B)=((20.2K kg mol^(-1))xx(6.2g))/((8.45K)xx(0.0983 kg))=158.0 g mool^(-1)`