   Chapter 11, Problem 120CP

Chapter
Section
Textbook Problem

# Plants that thrive in salt water must have internal solutions (inside the plant cells) that are isotonic with (have the same osmotic pressure as) the surrounding solution. A leaf of a saltwater plant is able to thrive in an aqueous salt solution (at 25°C) that has a freezing point equal to −0.62l°C. You would like to use this information to calculate the osmotic pressure of the solution in the cell.a. In order to use the freezing-point depression to calculate osmotic pressure, what assumption must you make (in addition to ideal behavior of the solutions, which we will assume)?b. Under what conditions is the assumption (in part a) reasonable?c. Solve for the osmotic pressure (at 25°C) of the solution in the plant cell.d. The plant leaf is placed in an aqueous salt solution (at 25°C) that has a boiling point of l02.0°C. What will happen to the plant cells in the leaf?

a)

Interpretation Introduction

Interpretation: The conditions and assumption for the freezing point calculation, the calculation of osmotic pressure and state of leaf after boiling at certain temperature has to be explained.

Concept Introduction:

Colligative properties of a substance include the depression in the freezing point, elevation of boiling-point and osmotic pressure. These are dependant only on the number present and not based on the solute particles present in an ideal solution.

The depression in freezing point can be given by the equation,

ΔT=Kfmsolute

Where, ΔT =change in freezing point depression

Kf = molal freezing point depression constant

msolute = molality of solute

Explanation

To explain the assumption made for ideal solution where the freezing point is used to calculate the osmotic pressure.

The depression in freezing point can be given by the equation,

ΔT=Kfmsolute

Where, ΔT =change in freezing point depression

Kf = molal freezing point depression constant

msolute = molality of solute

The osmotic pressure can be given by the equation,

Π=MRT

Here,Π=Osmoticpressure

b)

Interpretation Introduction

Interpretation: The conditions and assumption for the freezing point calculation, the calculation of osmotic pressure and state of leaf after boiling at certain temperature has to be explained.

Concept Introduction:

Colligative properties of a substance include the depression in the freezing point, elevation of boiling-point and osmotic pressure. These are dependant only on the number present and not based on the solute particles present in an ideal solution.

The depression in freezing point can be given by the equation,

ΔT=Kfmsolute

Where, ΔT =change in freezing point depression

Kf = molal freezing point depression constant

msolute = molality of solute

c)

Interpretation Introduction

Concept Introduction:

Colligative properties of a substance include the depression in the freezing point, elevation of boiling-point and osmotic pressure. These are dependant only on the number present and not based on the solute particles present in an ideal solution.

The osmotic pressure can be given by the equation,

Π=MRT

Here,Π=OsmoticpressureM=MolarityofsolutionR=GaslawconstantT=Temperature

d)

Interpretation Introduction

Concept Introduction:

The depression in freezing point, the elevation of boiling point and osmotic pressure are together known as colligative properties.

The elevation in boiling point changed can be given by the equation,

ΔT=Kbmsolute

Where, ΔT = change in boiling point elevation

Kb = molal boiling point elevation constant

msolute = molality of solute

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