   Chapter 13, Problem 37PS

Chapter
Section
Textbook Problem

An aqueous solution contains 3.00% phenylalanine (C9H11NO2) by mass. (Phenylalanine is non-ionic and nonvolatile.) Find the following: (a) the freezing point of the solution (b) the boiling point of the solution (c) the osmotic pressure of the solution at 25 °C In your view, which of these values is most easily measurable in the laboratory?

(a)

Interpretation Introduction

Interpretation: The freezing point of the given solution 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 elevation constant.

Molality (m): Molality is the number of moles of solute present in one kilogram of solvent.

Molality (m) =Numberofmolesofsolute1kgofsolvent

Explanation

Given,

Mass of phenylalanine is 3%=3100×100g=3g

Mass of solvent is 100g3g=97g=0.097kg

Molar mass of phenylalanine is 165.19g/mol

Molal freezing point elevation constant of water is 1.860Cm1

Numberofmole=GivenmassofthesubstanceMolarmass=3gphenylalanine165.19g/mol=0

(b)

Interpretation Introduction

Interpretation: The boiling point of the given solution 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.

Molality (m): Molality is the number of moles of solute present in one kilogram of solvent.

Molality (m) =Numberofmolesofsolute1kgofsolvent

(c)

Interpretation Introduction

Interpretation: The osmotic pressure of the given solution has to be determined. The values that are easily measureable in laboratory have to be identified among these values.

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

Osmotic pressure is calculated by using the equation,

π=cRT

where,

c is the molar concentration.

Molality (m): Molality is the number of moles of solute present in one kilogram of solvent.

Molality (m) =Numberofmolesofsolute1kgofsolvent

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