Hoa dai cuong_chuong 14

Philip Dutton
University of Windsor, Canada
N9B 3P4

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General Chemistry
Principles and Modern Applications
Petrucci • Harwood • Herring
8th Edition
Chapter 14: Solutions and Their
Physical Properties
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General Chemistry: Chapter 14
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Contents
14-1 Types of Solutions: Some Terminology
14-2 Solution Concentration
14-3 Intermolecular Forces and the Solution Process
14-4 Solution Formation and Equilibrium
14-5 Solubilities of Gases
14-6 Vapor Pressure of Solutions
14-7 Osmotic Pressure
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Contents
14-8 Freezing-Point Depression and Boiling-Point Elevation of Nonelectrolyte solutions.
14-9 Solutions of Electrolytes
14-10 Colloidal Mixtures
Focus on Chromatography
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13-1 Types of Solution:
Some Terminology
Solutions are homogeneous mixtures.
Uniform throughout.
Solvent.
Determines the state of matter in which the solution exists.
Is the largest component.
Solute.
Other solution components said to be dissolved in the solution.
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Table 14.1 Some Common Solutions
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14-2 Solution Concentration.
Mass percent. (m/m)
Volume percent. (v/v)
Mass/volume percent. (m/v)

Isotonic saline is prepared by dissolving 0.9 g of NaCl in 100 mL of water and is said to be:
0.9% NaCl (mass/volume)
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10% Ethanol Solution (v/v)
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ppm, ppb and ppt
Very low solute concentrations are expressed as:

ppm: parts per million (g/g, mg/L)
ppb: parts per billion (ng/g, g/L)
ppt: parts per trillion (pg/g, ng/L)

note that 1.0 L  1.0 g/mL = 1000 g
ppm, ppb, and ppt are properly m/m or v/v.
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Mole Fraction and Mole Percent
 =
Amount of component i (in moles)
Total amount of all components (in moles)
1 + 2 + 3 + …n = 1
Mole % i = i  100%
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Molarity and Molality
Molarity (M) =
Amount of solute (in moles)
Volume of solution (in liters)
Molality (m) =
Amount of solute (in moles)
Mass of solvent (in kilograms)
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14-3 Intermolecular Forces and the Solution Process
ΔHa
ΔHb
ΔHc
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Intermolecular Forces in Mixtures
Magnitude of ΔHa, ΔHb, and ΔHc depend on intermolecular forces.

Ideal solution
Forces are similar between all combinations of components.
ΔHsoln = 0
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Ideal Solution
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Non-ideal Solutions
Adhesive forces greater than cohesive forces.
ΔHsoln < 0
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Non-ideal Solutions
Adhesive forces are less than cohesive forces.




At the limit these solutions are heterogeneous.
ΔHsoln > 0
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Ionic Solutions
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Hydration Energy
NaCl(s) → Na+(g) + Cl-(g) ΔHlattice > 0

Na+(g) + xs H2O(l) → Na+(aq) ΔHhydration < 0

Cl-(g) + xs H2O(l) → Cl-(aq) ΔHhydration < 0
ΔHsoln > 0 but ΔGsolution < 0
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14-4 Solution Formation and Equilibrium
saturated
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Solubility Curves
Supersaturated Unsaturated
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14-5 Solubility of Gases
Most gases are less soluble in water as temperature increases.
In organic solvents the reverse is often true.
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Henry’s Law
Solubility of a gas increases with increasing pressure.
C = k Pgas
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Henry’s Law
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14-6 Vapor Pressures of Solutions
Roault, 1880s.
Dissolved solute lowers vapor pressure of solvent.
The partial pressure exerted by solvent vapor above an ideal solution is the product of the mole fraction of solvent in the solution and the vapor pressure of the pure solvent at a given temperature.

PA = A P°
A
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Example 14-6
Predicting vapor pressure of ideal solutions.
The vapor pressures of pure benzene and toluene at 25°C are 95.1 and 28.4 mm Hg, respectively. A solution is prepared in which the mole fractions of benzene and toluene are both 0.500. What are the partial pressures of the benzene and toluene above this solution? What is the total vapor pressure?
Balanced Chemical Equation:
Pbenzene = benzene P°benzene = (0.500)(96.1 mm Hg) = 47.6 mm Hg
Ptoluene = toluene P°toluene = (0.500)(28.4 mm Hg) = 14.2 mm Hg
Ptotal = Pbenzene + Ptoluene = 61.8 mm Hg
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Example 14-7
Calculating the Composition of Vapor in Equilibrium with a Liquid Solution.
What is the composition of the vapor in equilibrium with the benzene-toluene solution?
Partial pressure and mole fraction:
benzene = Pbenzene/Ptotal = 47.6 mm Hg/61.89 mm Hg = 0.770
toluene = Ptoluene/Ptotal = 14.2 mm Hg/61.89 mm Hg = 0.230
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Liquid-Vapor Equilibrium
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Fractional Distillation
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Fractional Distillation
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Non-ideal behavior
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14-7 Osmotic Pressure
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Osmotic Pressure
πV = nRT
= M RT
For dilute solutions of electrolytes:
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Osmotic Pressure
Isotonic Saline 0.92% m/V
Hypertonic > 0.92% m/V
crenation
Hypotonic > 0.92% m/V
rupture
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Reverse Osmosis - Desalination
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14-8 Freezing-Point Depression and Boiling Point Elevation of Nonelectrolyte Solutions
Vapor pressure is lowered when a solute is present.
This results in boiling point elevation.
Freezing point is also effected and is lowered.
Colligative properties.
Depends on the number of particles present.
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Vapor Pressure Lowering
ΔTf = -Kf  m
ΔTb = -Kb  m
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Practical Applications
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14-9 Solutions of Electrolytes
Svante Arrhenius
Nobel Prize 1903.
Ions form when electrolytes dissolve in solution.
Explained anomalous colligative properties
ΔTf = -Kf  m = -1.86°C m-1  0.0100 m = -0.0186°C
Compare 0.0100 m aqueous urea to 0.0100 m NaCl (aq)
Freezing point depression for NaCl is -0.0361°C.
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van’t Hoff
ΔTf = -i  Kf  m
i = = = 1.98
measured ΔTf
ΔTb = -i  Kb  m
expected ΔTf
0.0361°C
0.0186°C
π = -i  M  RT
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Interionic Interactions
Arrhenius theory does not correctly predict the conductivity of concentrated electrolytes.
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Debye and Hückel
1923
Ions in solution do not behave independently.
Each ion is surrounded by others of opposite charge.
Ion mobility is reduced by the drag of the ionic atmosphere.
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14-10 Colloidal Mixtures
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Colloids
Particles of 1-1000 nm size.
Nanoparticles of various shapes: rods, discs, spheres.
Particles can remain suspended indefinitly.
Milk is colloidal.
Increasing ionic strength can cause precipitation.

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Dialysis
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Focus on Chromatography
Stationary Phase
silicon gum
alumina
silica
Mobile Phase
solvent
gas
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Chromatography
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Chapter 14 Questions

Develop problem solving skills and base your strategy not on solutions to specific problems but on understanding.

Choose a variety of problems from the text as examples.

Practice good techniques and get coaching from people who have been here before.