Chapter 13, Problem 66GQ

### 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

# The smell of ripe raspberries is due to 4-(p-hydroxyphenyl)-2-butanone, which has the empirical formula C5H6O. To find its molecular formula, you dissolve 0.135 g in 25.0 g of chloroform, CHCl3. The boiling point of the solution is 61.82 °C. What is the molecular formula of the solute?

Interpretation Introduction

Interpretation: The molar mass and its molecular formula of 4-(p-hydroxyphenyl)-2-butanone is 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

Boiling point elevation: The boiling point of the solution varies with the solute concentration.

ΔTbp=Kbpmsolute

where,

Kbp is the molal boiling point elevation constant.

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

Numberofmole=GivenmassofthesubstanceMolarmass

Explanation

The molar mass and its molecular formula of 4-(p-hydroxyphenyl)-2-butanone is calculated.

Given,

â€‚Â Î”Tâ€‰=â€‰(61.820Câ€‰âˆ’â€‰61.700Câ€‰)â€‰=â€‰0.120C

â€‚Â Mass of 4-(p-hydroxyphenyl)-2-butanone is 0.135â€‰g

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

â€‚Â Molal boiling point elevation constant of chloroform is 3.630C/m

Change in boiling point is calculated by using the equation,

â€‚Â Î”Tbpâ€‰=â€‰Kbpâ€‰msolute

Hence,

The concentration is calculated by,

â€‚Â Concentration,msolute=â€‰Î”TbpKbp=â€‰(â€‰0.120C)(3.630C/m)=â€‰0.0331â€‰m

The amount of 4-(p-hydroxyphenyl)-2-butanone is,

â€‚Â (â€‰0.0331â€‰m1â€‰kg)â€‰(0.025â€‰kg)=â€‰8

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