Chapter 13, Problem 41PS

### 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

# You add 0.255 g of an orange, crystalline compound whose empirical formula is C10H8Fe to 11.12 g of benzene. The boiling point of the benzene rises from 80.10 °C to 80.26 °C. What are the molar mass and molecular formula of the compound?

Interpretation Introduction

Interpretation: The molar mass and its molecular formula of the compound 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 boiling point is calculated by using the equation,

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 the compound are determined.

Given,

â€‚Â Î”Tâ€‰=â€‰(80.260Câ€‰âˆ’â€‰80.100Câ€‰)â€‰=â€‰0.160C

â€‚Â Mass of orange crystalline compound is 0.255â€‰g

â€‚Â Mass of benzene is 11.12â€‰gâ€‰=â€‰0.01112â€‰kg

â€‚Â Molal boiling point elevation constant of benzene is 2.530C/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€‰(0.160C)(2.530C/m)=â€‰0.06324â€‰m

The amount of compound dissolved is,

â€‚Â (0.06324â€‰mol1â€‰kg)â€‰(0.01112â€‰kg)=â€‰7

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