chapter 11 properties of solutions. chapter 11 table of contents copyright © cengage learning. all...

Chapter 11

Properties of Solutions

Chapter 11

Table of Contents

Copyright © Cengage Learning. All rights reserved 2

11.1 Solution Composition

11.2 The Energies of Solution Formation

11.3 Factors Affecting Solubility

11.4 The Vapor Pressures of Solutions

11.5 Boiling-Point Elevation and Freezing-Point Depression

11.6 Osmotic Pressure

11.7 Colligative Properties of Electrolyte Solutions

11.8 Colloids

Section 11.1

Solution Composition


Return to TOC

Various Types of Solutions

ExampleState of Solution State of Solute

State of Solvent

Air, natural gas Gas Gas Gas

Vodka, antifreeze Liquid Liquid Liquid

Brass Solid Solid Solid

Carbonated water (soda) Liquid Gas Liquid

Seawater, sugar solution Liquid Solid Liquid

Hydrogen in platinum Solid Gas Solid

Section 11.1



Return to TOC


AA

moles of soluteMolarity ( ) =

liters of solution

mass of soluteMass (weight) percent = 100%

mass of solution

molesMole fraction ( ) =

total moles of solution

moles of soluteMolality ( ) =

kilogram of s

M

molvent

Section 11.1



Return to TOC

Molarity

moles of soluteMolarity ( ) =

liters of solution M

Section 11.1



Return to TOC

Exercise

You have 1.00 mol of sugar in 125.0 mL of solution. Calculate the concentration in units of molarity.

8.00 M

Section 11.1



Return to TOC

Exercise

You have a 10.0 M sugar solution. What volume of this solution do you need to have 2.00 mol of sugar?

0.200 L

Section 11.1



Return to TOC

Exercise

Consider separate solutions of NaOH and KCl made by dissolving 100.0 g of each solute in 250.0 mL of solution. Calculate the concentration of each solution in units of molarity.

10.0 M NaOH

5.37 M KCl

Section 11.1



Return to TOC

Mass Percent

mass of soluteMass (weight) percent = 100%

mass of solution

Section 11.1



Return to TOC

Exercise

What is the percent-by-mass concentration of glucose in a solution made my dissolving 5.5 g of glucose in 78.2 g of water?

6.6%

Section 11.1



Return to TOC

Mole Fraction

AA

molesMole fraction ( ) =

total moles of solution

Section 11.1



Return to TOC

Exercise

A solution of phosphoric acid was made by dissolving 8.00 g of H3PO4 in 100.0 mL of water. Calculate the mole fraction of H3PO4. (Assume water has a density of 1.00 g/mL.)

0.0145

Section 11.1



Return to TOC

Molality

moles of soluteMolality ( ) =

kilogram of solvent m

Section 11.1



Return to TOC

Exercise

A solution of phosphoric acid was made by dissolving 8.00 g of H3PO4 in 100.0 mL of water. Calculate the molality of the solution. (Assume water has a density of 1.00 g/mL.)

0.816 m

Section 11.2

Atomic Masses


The Energies of Solution Formation

Return to TOC

Formation of a Liquid Solution

1. Separating the solute into its individual components (expanding the solute).

2. Overcoming intermolecular forces in the solvent to make room for the solute (expanding the solvent).

3. Allowing the solute and solvent to interact to form the solution.

Section 11.2

Atomic Masses



Return to TOC

Steps in the Dissolving Process

Section 11.2

Atomic Masses



Return to TOC

Steps in the Dissolving Process

• Steps 1 and 2 require energy, since forces must be overcome to expand the solute and solvent.

• Step 3 usually releases energy.• Steps 1 and 2 are endothermic, and step 3 is

often exothermic.

Section 11.2

Atomic Masses



Return to TOC

Enthalpy (Heat) of Solution

• Enthalpy change associated with the formation of the solution is the sum of the ΔH values for the steps:

ΔHsoln = ΔH1 + ΔH2 + ΔH3

• ΔHsoln may have a positive sign (energy absorbed) or a negative sign (energy released).

Section 11.2

Atomic Masses



Return to TOC

Enthalpy (Heat) of Solution

Section 11.2

Atomic Masses



Return to TOC

Concept Check

Explain why water and oil (a long chain hydrocarbon) do not mix. In your explanation, be sure to address how ΔH plays a role.

Section 11.2

Atomic Masses



Return to TOC

The Energy Terms for Various Types of Solutes and Solvents

H1 H2 H3 Hsoln Outcome

Polar solute, polar solvent Large Large Large, negative Small Solution forms

Nonpolar solute, polar solvent Small Large Small Large, positive No solution forms

Nonpolar solute, nonpolar solvent

Small Small Small Small Solution forms

Polar solute, nonpolar solvent Large Small Small Large, positive No solution forms

Section 11.2

Atomic Masses



Return to TOC

In General

• One factor that favors a process is an increase in probability of the state when the solute and solvent are mixed.

• Processes that require large amounts of energy tend not to occur.

• Overall, remember that “like dissolves like”.

Section 11.3

The Mole Factors Affecting Solubility


Return to TOC

• Structural Effects: Polarity

• Pressure Effects: Henry’s law

• Temperature Effects: Affecting aqueous solutions

Section 11.3



Return to TOC

Pressure Effects

• Henry’s law: C = kPC = concentration of dissolved gas

k = constant

P = partial pressure of gas solute above the solution

• Amount of gas dissolved in a solution is directly proportional to the pressure of the gas above the solution.

Section 11.3



Return to TOC

A Gaseous Solute

Section 11.3



Return to TOC

Temperature Effects (for Aqueous Solutions)

• Although the solubility of most solids in water increases with temperature, the solubilities of some substances decrease with increasing temperature.

• Predicting temperature dependence of solubility is very difficult.

• Solubility of a gas in solvent typically decreases with increasing temperature.

Section 11.3



Return to TOC

The Solubilities of Several Solids as a Function of Temperature

Section 11.3



Return to TOC

The Solubilities of Several Gases in Water

Section 11.4

The Vapor Pressures of Solutions


Return to TOC

An Aqueous Solution and Pure Water in a Closed Environment

Section 11.4



Return to TOC

Liquid/Vapor Equilibrium

Section 11.4



Return to TOC

Vapor Pressure Lowering: Addition of a Solute

Section 11.4



Return to TOC

Vapor Pressures of Solutions

• Nonvolatile solute lowers the vapor pressure of a solvent.

• Raoult’s Law:

Psoln = observed vapor pressure of

solution

solv = mole fraction of solvent

= vapor pressure of pure solvent

soln solv solv = P P

solvP

Section 11.4



Return to TOC

A Solution Obeying Raoult’s Law

Section 11.4



Return to TOC

Nonideal Solutions

• Liquid-liquid solutions where both components are volatile.

• Modified Raoult’s Law:

• Nonideal solutions behave ideally as the mole fractions approach 0 and 1.

Total A A B B = + P P P

Section 11.4



Return to TOC

Vapor Pressure for a Solution of Two Volatile Liquids

Section 11.4



Return to TOC

Summary of the Behavior of Various Types of Solutions

Interactive Forces Between Solute (A) and Solvent (B)

ParticlesHsoln

T for Solution Formation

Deviation from

Raoult’s Law

Example

A A, B B A B Zero ZeroNone (ideal

solution)Benzene-toluene

A A, B B < A BNegative

(exothermic)Positive Negative

Acetone-water

A A, B B > A BPositive

(endothermic)Negative Positive

Ethanol-hexane

Section 11.4



Return to TOC

Concept Check

For each of the following solutions, would you expect it to be relatively ideal (with respect to Raoult’s Law), show a positive deviation, or show a negative deviation?

a) Hexane (C6H14) and chloroform (CHCl3)

b) Ethyl alcohol (C2H5OH) and water

c) Hexane (C6H14) and octane (C8H18)

Section 11.5

Boiling-Point Elevation and Freezing-Point Depression


Return to TOC

• Depend only on the number, not on the identity, of the solute particles in an ideal solution: Boiling-point elevation Freezing-point depression Osmotic pressure

Colligative Properties

Section 11.5



Return to TOC

• Nonvolatile solute elevates the boiling point of the solvent.

• ΔT = Kbmsolute

ΔT = boiling-point elevation

Kb = molal boiling-point elevation constant

msolute= molality of solute

Boiling-Point Elevation

Section 11.5



Return to TOC

Boiling Point Elevation: Liquid/Vapor Equilibrium

Section 11.5



Return to TOC

Boiling Point Elevation: Addition of a Solute

Section 11.5



Return to TOC

Boiling Point Elevation: Solution/Vapor Equilibrium

Section 11.5



Return to TOC

• When a solute is dissolved in a solvent, the freezing point of the solution is lower than that of the pure solvent.

• ΔT = Kfmsolute

ΔT = freezing-point depression

Kf = molal freezing-point depression

constant

msolute= molality of solute

Freezing-Point Depression

Section 11.5



Return to TOC

Freezing Point Depression: Solid/Liquid Equilibrium

Section 11.5



Return to TOC

Freezing Point Depression: Addition of a Solute

Section 11.5



Return to TOC

Freezing Point Depression: Solid/Solution Equilibrium

Section 11.5



Return to TOC

Changes in Boiling Point and Freezing Point of Water

Section 11.5



Return to TOC

Exercise

A solution was prepared by dissolving 25.00 g glucose in 200.0 g water. The molar mass of glucose is 180.16 g/mol. What is the boiling point of the resulting solution (in °C)? Glucose is a molecular solid that is present as individual molecules in solution.

100.35 °C

Section 11.5



Return to TOC

Exercise

You take 20.0 g of a sucrose (C12H22O11) and NaCl mixture and dissolve it in 1.0 L of water. The freezing point of this solution is found to be -0.426°C. Assuming ideal behavior, calculate the mass percent composition of the original mixture, and the mole fraction of sucrose in the original mixture.

72.8% sucrose and 27.2% sodium chloride;

mole fraction of the sucrose is 0.313

Section 11.5



Return to TOC

Exercise

A plant cell has a natural concentration of 0.25 m. You immerse it in an aqueous solution with a freezing point of –0.246°C. Will the cell explode, shrivel, or do nothing?

Section 11.6

Osmotic Pressure


Return to TOC

• Osmosis – flow of solvent into the solution through a semipermeable membrane.

• = MRT

= osmotic pressure (atm)

M = molarity of the solution

R = gas law constant

T = temperature (Kelvin)

Section 11.6

Osmotic Pressure


Return to TOC

Section 11.6

Osmotic Pressure


Return to TOC

Osmosis

Section 11.6

Osmotic Pressure


Return to TOC

Section 11.6

Osmotic Pressure


Return to TOC

Exercise

When 33.4 mg of a compound is dissolved in 10.0 mL of water at 25°C, the solution has an osmotic pressure of 558 torr. Calculate the molar mass of this compound.

111 g/mol

Section 11.7

Colligative Properties of Electrolyte Solutions


Return to TOC

• The relationship between the moles of solute dissolved and the moles of particles in solution is usually expressed as:

van’t Hoff Factor, i

moles of particles in solution =

moles of solute dissolvedi

Section 11.7



Return to TOC

Ion Pairing

• At a given instant a small percentage of the sodium and chloride ions are paired and thus count as a single particle.

Section 11.7



Return to TOC

• The expected value for i can be determined for a salt by noting the number of ions per formula unit (assuming complete dissociation and that ion pairing does not occur). NaCl i = 2 KNO3 i = 2

Na3PO4 i = 4

Examples

Section 11.7



Return to TOC

• Ion pairing is most important in concentrated solutions.

• As the solution becomes more dilute, the ions are farther apart and less ion pairing occurs.

• Ion pairing occurs to some extent in all electrolyte solutions.

• Ion pairing is most important for highly charged ions.

Ion Pairing

Section 11.7



Return to TOC

Modified Equations

= T imK

= iMRT

Section 11.8

Colloids


Return to TOC

• A suspension of tiny particles in some medium.

• Tyndall effect – scattering of light by particles.

• Suspended particles are single large molecules or aggregates of molecules or ions ranging in size from 1 to 1000 nm.

Section 11.8

Colloids


Return to TOC

Types of Colloids

Section 11.8

Colloids


Return to TOC

• Destruction of a colloid.• Usually accomplished either by heating or

by adding an electrolyte.

Coagulation

chapter 11 properties of solutions. chapter 11 table of contents copyright © cengage learning. all...

Documents

solution compositionreturn

solution composition11

g of water

g of h3po4

dissolving processsection

g of glucose

dissolving processsteps

mol of sugar