Question 15 of 22 Map General Chemistr University Science Books presented by Sap

Question

Question 15 of 22 Map General Chemistr University Science Books presented by Sapling Lea Donald McQuarrie. Peter A Rock .Ethan Gallogly nthol is a crystalline substance with a peppermint taste and odor. When 1.18 g of menthol is dissolved in 25.0 g of cyclohexane, the freezing point of the solution is lowered by 6.30 °C. The freezing point and Kf constant for cyclohexane can be found here. Calculate the molar mass of menthol. Number g/mol Previous Give up & View Solution Check Answer Next xit ® 8 Hint Start by finding the molality, m (or b), of the solution using AT K, m where AT is the freezing-point depression, and Kf is a constant unique to the solvent.

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 as6.3 degc, molality of solute is{ [ 1.18/m ] / 25 } * 1000 = 47.2 / m where m is molar mass

g / mol of quinine , Kf is given as 20.8, Vant hoff factor for quinine is 1,

therefore,6.3 = 47.2/m * 20.8 or m =47.2*20.8/6.3 this equals to 155.83

Answer therefore is molar mass of quinine is 155.83 g/ mol

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