   Chapter 13, Problem 34PS

Chapter
Section
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:

ΔTfp =Thefreezingpointofthesolution-freezingpointofwaterΔTfp= -15.0oC-0.0oC=-15.0oCFreezing point of water = 0oCKfp ofWater=-1.86oC/mAmountofsolvent=5kg

Calculate the molality of solute in solution(m):_Freezing point Depression, ΔTfp= Kfp. msolute,-15.0oC=(-1.86oC/m)(msolute)msolute=-15

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