Menthol is crystalline substance with a peppermint taste and odor. When 0.527 g

Question

Menthol is crystalline substance with a peppermint taste and odor. When 0.527 g of menthol is dissolved in 25.0g of cyclohexane, the freezing point of the solution is lowered by 2.71 dergrees C. Calculate the molar mass of menthol. Menthol is crystalline substance with a peppermint taste and odor. When 0.527 g of menthol is dissolved in 25.0g of cyclohexane, the freezing point of the solution is lowered by 2.71 dergrees C. Calculate the molar mass of menthol. When 0.527 g of menthol is dissolved in 25.0g of cyclohexane, the freezing point of the solution is lowered by 2.71 dergrees C. Calculate the molar mass of menthol.

Explanation / Answer

Depression of freezing point is expressed as

Tf = molality * Kf * i

Kf = freezing point constant [ cryoscopic constant ]

i = Van't Hoff factor

Tf given as 2.71 degc,

molality of solute is moles of solute in 1 kg of solvent (1000 g of solvent)

Moles = mass (g) / molar mass (g/mol)

{ [ 0.527 g / M. Wt(g/mol) ] / 0.025 kg of cyclohexane} = 21.08 / M. Wt
Kf of cyclohexane is 20.8, Vant hoff factor for menthol is 1,

therefore, 2.71 = (21.08/ M. Wt) * 20.8 * 1

M. Wt = 21.08 *20.8/ 2.71 => 161.8 g/mol

Answer molar mass of menthol = 161.8 g/mol

Answer therefore is molar mass of quinine is 324.3 g/ mol

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