   Chapter 13, Problem 41PS

Chapter
Section
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,

ΔT=(80.260C80.100C)=0.160C

Mass of orange crystalline compound is 0.255g

Mass of benzene is 11.12g=0.01112kg

Molal boiling point elevation constant of benzene is 2.530C/m

Change in boiling point is calculated by using the equation,

ΔTbp=Kbpmsolute

Hence,

The concentration is calculated by,

Concentration,msolute=ΔTbpKbp=(0.160C)(2.530C/m)=0.06324m

The amount of compound dissolved is,

(0.06324mol1kg)(0.01112kg)=7

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