Chapter 13, Problem 53GQ

### 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

# 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,

â€‚Â Î”Tâ€‰=â€‰âˆ’0.360C

â€‚Â Mass of phenylcarbinol is 0.52â€‰g

â€‚Â Mass of water is 25â€‰gâ€‰=â€‰0.025â€‰kg

â€‚Â Molal freezing point depression constant of water is â€‰âˆ’1.860C/m

Change in melting point is calculated by using the equation,

â€‚Â Î”Tfpâ€‰=â€‰Kfpâ€‰msolute

Hence,

The concentration is calculated by,

â€‚Â Concentration,msolute=â€‰Î”TfpKfp=â€‰(âˆ’0.360C)(âˆ’1.860C/m)=â€‰0.19355â€‰m

MolalityÂ (m)Â =Numberâ€‰ofâ€‰molesâ€‰ofâ€‰solute1kgâ€‰ofâ€‰solvent

The number of moles of phenylcarbinol is,

â€‚Â (â€‰0

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