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Chapter 14 1 Solutions and Their Solutions and Their Behavior Behavior Chapter Chapter 14 14
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Chapter 14 1
Solutions and Their Solutions and Their BehaviorBehavior
Chapter 14Chapter 14
Chapter 14 2
The Solution ProcessThe Solution ProcessSolution - A homogeneous mixture composed of a solute
and a solvent.
Solute – The substance which is dissolved.
Solvent – The substance which acts as the dissolving medium.
Chapter 14 3
Saturated Solutions and SolubilitySaturated Solutions and SolubilityMole Fraction, Molarity, and MolalityMole Fraction, Molarity, and MolalityQualitative Terms:
Dilute Solution – A solution in which additional solute may be dissolved.
Saturated Solution – A solution in which no more solute may be dissolved.
Supersaturated Solution – A solution in which more solute is dissolved than in a saturated solution.
Solubility - amount of solute required to form a saturated solution.
Chapter 14 4
Ways of Expressing ConcentrationWays of Expressing Concentration• Definitions:
100soln of mass total
soln incomponent of mass % Mass
610soln of mass total
soln incomponent of massppm
Chapter 14 5
Ways of Expressing ConcentrationWays of Expressing ConcentrationMole Fraction, Molarity, and MolalityMole Fraction, Molarity, and MolalityMole Fraction
Molarity
components all of moles total
component of molesfraction Mole
solution of liters
solute of molesMolarity
Chapter 14 6
Ways of Expressing ConcentrationWays of Expressing ConcentrationMole Fraction, Molarity, and MolalityMole Fraction, Molarity, and MolalityMolality (m) – moles of solute per kilogram of solution
solvent of kilograms
solute of molesMolality
Chapter 14 7
The Solution ProcessThe Solution ProcessLiquids Dissolving in LiquidsLiquids Dissolving in Liquids
Miscible liquids - Mix in any proportions.
Immiscible liquids - Do not mix.
Chapter 14 8
The Solution ProcessThe Solution ProcessLiquids Dissolving in LiquidsLiquids Dissolving in Liquids
“Like Dissolves Like”• Polar molecules will dissolve in polar solvents.• Non-polar molecules will dissolve in non-polar
solvents.
Chapter 14 9
The Solution ProcessThe Solution ProcessSolids Dissolving in LiquidsSolids Dissolving in Liquids
“Like Dissolves Like”• Still true but less effective (i.e. there are exceptions)• Also, many dissolution processes are endothermic.
• A classic example is Ammonium nitrate in water.• A classic exception is Sulfuric acid in water.
Chapter 14 10
The Solution ProcessThe Solution ProcessHeat of SolutionHeat of SolutionFor a solid to dissolve:• Energy must be supplied to separate the ions in the
crystal lattice: -Hlattice
• Energy is evolved individual items are surrounded by the solvent: Hhydration
Hsolution = (-Hlattice + Hhydration)
Chapter 14 11
Factors Affecting SolubilityFactors Affecting SolubilityTemperature EffectsTemperature Effects
Chapter 14 12
Factors Affecting SolubilityFactors Affecting Solubility
Pressure EffectsPressure Effects• Solubility of a gas in a liquid is a function of the
pressure of the gas.• The higher the pressure, the greater the solubility.
Chapter 14 13
Factors Affecting SolubilityFactors Affecting Solubility
Pressure EffectsPressure EffectsHenry’s Law – The solubility of a gas increases in direct
proportion to its partial pressure above the solution.
Sg - solubility of gas
Pg - the partial pressure of the gas
kH - Henry’s law constant.
gHg PkS
Chapter 14 14
Factors Affecting SolubilityFactors Affecting SolubilityTemperature EffectsTemperature Effects
Chapter 14 15
Factors Affecting SolubilityFactors Affecting SolubilityTemperature EffectsTemperature Effects• The solubility of a gas is greater in a cold solvent.• The dissolution of a gas in water is an exothermic
process.
Chapter 14 16
Colligative PropertiesColligative Properties• Properties of a solution which depend on quantity of
solute molecules. • Solutions formed with a nonvolatile solute will:
• have lower vapor pressure• lower freezing point• higher boiling point
Chapter 14 17
Colligative PropertiesColligative Properties
Boiling-Point ElevationBoiling-Point Elevation
Chapter 14 18
Colligative PropertiesColligative Properties
Raoult’s LawRaoult’s LawRaoult’s Law – The equilibrium vapor pressure of the
solvent over the solution is directly proportional to the mole fraction of the solvent in the solution
Psolvent - vapor pressure of the solvent in the solution
Psolvent - vapor pressure of the pure solvent
solvent - the mole fraction of solvent
osolventsolventsolvent PP
Chapter 14 19
Colligative PropertiesColligative Properties
Change in Vapor PressureChange in Vapor Pressure
Psolvent - vapor pressure of the solvent in the solution
Psolvent - vapor pressure of the pure solvent
solute - the mole fraction of solute
osolventsolutesolvent PP
Chapter 14 20
Colligative PropertiesColligative Properties
Boiling-Point ElevationBoiling-Point Elevation• As the vapor pressure of a solution decreases, the
boiling point increases.• Recall, a solvent boils when its’ vapor pressure equals
the atmospheric pressure.
Chapter 14 21
Colligative PropertiesColligative Properties
Boiling-Point ElevationBoiling-Point Elevation
Kbp - Molal boiling-point elevation constant
m – solution molality
Tbp – boiling point change
mKΔT bpbp
Chapter 14 22
Colligative PropertiesColligative Properties
Freezing-Point DepressionFreezing-Point Depression• Just as the boiling point is raised, the freezing point is
lowered.
Chapter 14 23
Colligative PropertiesColligative Properties
Freezing-Point DepressionFreezing-Point Depression
Kfp - Molal freezing-point depression constant
m – solution molality
Tfp – freezing point change
mKT fpfp
Chapter 14 24
Colligative PropertiesColligative Properties
F.Pt. and B.Pt. Change with Ionic SolutesF.Pt. and B.Pt. Change with Ionic Solutes• The previous equations assumed molecular solids
– example, sugar (C6H12O6)
)()( 612661262 aqOHCsOHC OH
• Recall that colligative properties are a function of the number of bodies in the solution.
)()()( 2 aqClaqNasNaCl OH
Chapter 14 25
Colligative PropertiesColligative Properties
F.Pt. and B.Pt. Change with Ionic SolutesF.Pt. and B.Pt. Change with Ionic Solutes• F. Pt. depression and B. Pt. equations must be
modified to account for this.
imKΔT bpbp
Kbp - Molal boiling-point elevation constant m – solution molalityTbp – boiling point changei – van Hoff factor
Chapter 14 26
Colligative PropertiesColligative Properties
F.Pt. and B.Pt. Change with Ionic SolutesF.Pt. and B.Pt. Change with Ionic Solutes
imKΔT fpfp
Kfp - Molal freezing-point depression constant m – solution molalityTfp – freezing point changei – van Hoff factor
Chapter 14 27
Colligative PropertiesColligative Properties
Molar Mass DeterminationMolar Mass DeterminationThe molar mass (molecular weight) can be determined by observing the freezing point change to a solution in which a know quantity of non-volatile solute has been added.
Chapter 14 28
Colligative PropertiesColligative PropertiesOsmosisOsmosisThe net movement of solvent through a semi-permeable
membrane from a dilute to a concentrated solution.
Chapter 14 29
Colligative PropertiesColligative PropertiesOsmosisOsmosisEventually the pressure difference between the arms
stops osmosis.
Chapter 14 30
Colligative PropertiesColligative PropertiesOsmosisOsmosisOsmotic pressure() - The pressure required to stop osmosis:
c - molarity of the solution
R - gas constant (0.08206 L(atm)/mol(K))
T - temperature in Kelvin
cRT
Chapter 14 31
ColloidsColloids• Colloids are suspensions in which the suspended
particles are larger than molecules but too small to drop out of the suspension due to gravity.
• Particle size: 10 to 2000 Å.
Chapter 14 32
ColloidsColloids• Tyndall effect: ability of a Colloid to scatter light.
The beam of light can be seen through the colloid.
Chapter 14 33
HomeworkHomework4, 8, 23, 28, 38,42, 52
