   Chapter 13, Problem 53GQ

Chapter
Section
Textbook Problem

Phenylcarbinol is used in nasal sprays as a preservative. A solution of 0.52 g of the compound in 25.0 g of water has a melting point of −0.36 °C. What is the molar mass of phenylcarbinol?

Interpretation Introduction

Interpretation: The molar mass of phenylcarbinol has to be determined.

Concept introduction:

Colligative properties: Properties of solutions which having influence on the concentration of the solute in it. Colligative properties are,

• Decrease in the vapor pressure
• Increase in the boiling point
• Decline in the freezing point
• Osmotic pressure

Change in freezing point is calculated by using the equation,

ΔTfp=Kfpmsolute

where,

Kfp is the molal freezing point depression constant.

The number of moles of any substance can be determined using the equation

Numberofmole=GivenmassofthesubstanceMolarmass

Explanation

The molar mass of phenylcarbinol is calculated.

Given,

ΔT=0.360C

Mass of phenylcarbinol is 0.52g

Mass of water is 25g=0.025kg

Molal freezing point depression constant of water is 1.860C/m

Change in melting point is calculated by using the equation,

ΔTfp=Kfpmsolute

Hence,

The concentration is calculated by,

Concentration,msolute=ΔTfpKfp=(0.360C)(1.860C/m)=0.19355m

Molality (m) =Numberofmolesofsolute1kgofsolvent

The number of moles of phenylcarbinol is,

(0

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