The freezing point of ethanol CH CHOH is-117.30°C at 1 atmosphere. A nonvolatile

Question

The freezing point of ethanol CH CHOH is-117.30°C at 1 atmosphere. A nonvolatile, nonelectrolyte that dissolves in ethanol is testosterone How many grams of testosterone, CioH2802 (28s.4 gmol), must be dissolved in 201.0 grams of ethanol to reduce the freezing point by 0.350°C ? Refer to the table for the necessary boiling or freezing point constant. ki,ecmy ???? 0.512 1.86 E Formula H2o Solvent Water Ethanol CH3CH OH 1.22 1.99 3.67 2.53 5.12 Chloroform CHCl Benzene CsH Diethyl ether CH3CH2OCH CH3 2.02 g testosterone

Explanation / Answer

Answer:

We know that, freezing-point depression is defirned as

?TF = i x KF x m

where ?TF =TF (pure solvent) ? TF (solution),

i= van 't Hoff factor, i =1 for non-electrolyte,

m= molality, moles of solute/mass of solvent (kg).

KF= the cryoscopic constant=1.99 °C.kg/mol for ethanol.

Given solvent is ethanol, TF(ethanol)= -117.30°C, mass of solvent=201 g=0.201 kg,

?TF=0.350°C,

Here solute is Testosterone, massof solute=? and molar mass of solute=288.4 g/mol.

?TF i x KF x [moles of solute/mass of solvent (kg)]

0.350°C= 1 x 1.99 °C.kg/mol x (moles of solute)/0.201 kg

moles of solute=(0.350°C x 0.201 kg)/1.99°C.kg/mol=0.03535 mol.

Mass of solute=moles x molar mass=0.03535 mol x 288.4 g/mol=10.195 g.

Therefore mass of testosterone=10.195 g.

Please let me know if you have any doubt. Thank you.

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