Chapter 13, Problem 34PS

### 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

# Some ethylene glycol, HOCH2CH2OH, is added to your car’s cooling system along with 5.0 kg of water. If the freezing point of the water-glycol solution is −15.0 °C, what mass of HOCH2CH2OH must have been added?

Interpretation Introduction

Interpretation: The mass of ethylene glycol has to be identified.

Concept introduction:

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

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

Explanation
• Calculate the molality of ethylene glycol:

Given data:

Î”TfpÂ =â€‰Theâ€‰freezingâ€‰pointâ€‰ofâ€‰theâ€‰solutionâ€‰â€‰-â€‰freezingâ€‰pointâ€‰ofâ€‰waterâ€‰Î”Tfpâ€‰â€‰=Â -15.0oCâ€‰-â€‰0.0oCâ€‰=â€‰-15.0oCFreezingÂ pointÂ ofÂ waterÂ =Â 0oCKfpÂ ofâ€‰Water=â€‰-1.86oC/mAmountâ€‰ofâ€‰solventâ€‰=â€‰5â€‰kg

CalculateÂ theÂ molalityÂ ofÂ soluteÂ inÂ solution(m):_FreezingÂ pointÂ Depression,Â Î”Tfp=Â Kfp.Â msolute,-15.0oCâ€‰â€‰â€‰â€‰â€‰=â€‰(-1.86oC/m)(msolute)msoluteâ€‰=â€‰-15

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