Chapter 13, Problem 33PS

### Chemistry & Chemical Reactivity

10th Edition
John C. Kotz + 3 others
ISBN: 9781337399074

Chapter
Section

### Chemistry & Chemical Reactivity

10th Edition
John C. Kotz + 3 others
ISBN: 9781337399074
Textbook Problem

# A mixture of ethanol C2H5OH, and water has a freezing point of −16.0 °C. (a) What is the molality of the alcohol? (b) What is the weight percent of alcohol in the solution?

(a)

Interpretation Introduction

Interpretation: The molality of the ethanol in a mixture of ethanol and water has to be identified.

Concept introduction:

Freezing point depression: The freezing point of the solution varies with the solute concentration.

Depression in Freezing point = ΔTfp= Kfp. msolute,where,Kfpismolal freezing point depression constant,msoluteis molality of solute

Weight percent: The mass of one component divided by the total mass of the mixture, multiplied by 100%

weight % A = Mass of A Mass of A + Mass of B + Mass of C + ...×100%

Explanation

Calculate the molality of ethanol:

Given data:

Î”Tfpâ€‰â€‰=Â -16.0oCâ€‰-â€‰0.0oCâ€‰=â€‰-16.0oCFreezingÂ pointÂ ofÂ waterÂ =Â 0oCKfpÂ ofâ€‰Water=â€‰-1.86oC/m

CalculationÂ ofÂ theÂ molalityÂ ofÂ soluteÂ inÂ solution(m):_FreezingÂ pointÂ Depression,Â Î”Tfp=Â Kfp

(b)

Interpretation Introduction

Interpretation: The weight percentage of the ethanol in a mixture of ethanol and water has to be identified.

Concept introduction:

Weight percent: The mass of one component divided by the total mass of the mixture, multiplied by 100%

weight % A = Mass of A Mass of A + Mass of B + Mass of C + ...×100%

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