o 2/11/2016 11:00 PM 0 842/1002/10/2016 04:51 PM Gradebook Print Calculator -d P

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o 2/11/2016 11:00 PM 0 842/1002/10/2016 04:51 PM Gradebook Print Calculator -d Periodic Table Question 7 of 13 Map University Science Books presented by Sapling Learning emi Donald McQuanrie P Peter A. Rock Ethan Galloghy Quinine is a natural product extracted from the bark of the cinchona tree, which is native to South America. Quinine is used as an antimalarial agent. When 1.12 g of quinine is dissolved in 25.0 g of cyclohexane, the freezing point of the solution is lowered by 2.87 °C. The freezing point and Kf constant for cyclohexane can be found here. Calculate the molar mass of quinine. Number g mol O Give Up & View Solution- Check Answer 0 Next Previous Exit Hi nt

Explanation / Answer

m = 1.12 g of quinine

m = 25 g of cylcohexane

dTf = 2.87 °C

For the solvent:

Kf = -20.2

Tf = 6.55°C

First, find mole of quionen since

Molar Weight = mass/mol

mass = 1.12

mol = ? from molality

dTf = - K*m

substitute values

2.87 = (20.2)(m)

m = 2.87 /20.2 = 0.142079 mol of quinone per kg of solvent

m solvent = 25 g = 0.025 kg

then

mol = molality*kg = 0.142079*0.025 = 0.003551975 mol of quinine

then

MW = 1.12/0.003551975 = 315.3175 g/mol

real value is around = 324.42 g/mol

NOTE:

there is either:

different values of Kf

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