Chapter 13, Problem 46PS

### 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

# 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,

â€‚Â Î”Tâ€‰=â€‰âˆ’0.1970C

â€‚Â Mass of aluminon is 2.50â€‰g

â€‚Â Mass of water is 50â€‰gâ€‰=â€‰0.050â€‰kg

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

Change in freezing 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”TfpKfp=â€‰(âˆ’0.1970C)(âˆ’1.860C/m)=â€‰0.1059â€‰m

The amount of aluminon is,

â€‚Â (â€‰0

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