   Chapter 13, Problem 46PS

Chapter
Section
Textbook Problem

Aluminon, an organic compound, is used as a reagent to test for the presence of the aluminum ion in aqueous solution. A solution of 2.50 g of aluminon in 50.0 g of water freezes at −0.197 °C. What is the molar mass of aluminon?

Interpretation Introduction

Interpretation: The molar mass of aluminon 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 aluminon is calculated.

Given,

ΔT=0.1970C

Mass of aluminon is 2.50g

Mass of water is 50g=0.050kg

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

Change in freezing point is calculated by using the equation,

ΔTbp=Kbpmsolute

Hence,

The concentration is calculated by,

Concentration,msolute=ΔTfpKfp=(0.1970C)(1.860C/m)=0.1059m

The amount of aluminon is,

(0

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