Download - Chapter 8 Liquids and Solutions
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Chapter 8Liquids and Solutions
As already mentioned in chapter 2, a lot of chemistry is done in solution, especially aqueous solution.
In this chapter we address issues that arise when dealing with solutions.
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The Structure of Gases, Liquids and Solids
Figure 8.1
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The Structure of Gases, Liquids and Solids
Table 8.1
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The Structure of Gases, Liquids and Solids
● Intramolecular bond● Intermolecular force
Figure 8.2
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Intermolecular Forces
● Absent in kinetic molecular theory.● In their absence, all matter is in the gas
phase.● Relative strength of intermolecular forces
established using boiling points.Low bp means weak intermolecular forces.
High bp means strong intermolecular forces.
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Intermolecular Forces
Five important types
dipole-dipole
dipole-induced dipole
induced dipole-induced dipole
van der Waals (aka London, dispersion)
Hydrogen bonding
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Intermolecular Forces
● dipole-dipole
Figure 8.3
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Intermolecular Forces
● dipole-induced dipole
Figure 8.4
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Intermolecular Forces
● induced dipole-induced dipole
Figure 8.5
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Intermolecular Forces
● van der WaalsWeak
Present in all systems.
Proportional to the number of electrons in the molecules.
Table 8.2
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Intermolecular Forces
● van der WaalsMW, Figure 8.8
Shape, Figure 8.7– n-pentane (bp 36.1 ⁰C) vs
neopentane (bp 9.5 ⁰C)
Figure 8.8Figure 8.7
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Intermolecular Forces
● Hydrogen bondingMisleading name
Possible in molecules with H - X bond where X is F, O, or N.
– Highlights importance of Lewis structure.
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Intermolecular Forces
...importance of Lewis structure
CC O
H
H
H
H
H
H O C H
H
H
CH
H
H
Two isomers, only one participates in hydrogen bonding.
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Intermolecular Forces
● Hydrogen bondingProfound consequences
Figure 8.9
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Intermolecular Forces
● Hydrogen bonding
...results in liquid water on Earth!!
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Relative Strengths of Intermolecular Forces
Table 8.3
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Relative Strengths of Intermolecular Forces
Table 8.5
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The Kinetic Theory of Liquids
● Average KE T (section 6.2).● Range of KE.● Intermolecular forces present.
That's why it's a liquid.
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The Kinetic Theory of Liquids
● Enthalpy of vaporization, ΔH°vap.
● Enthalpy of fusion, ΔH°fus.
● ΔH°vap >> ΔH°fus.
Why?
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The Vapor Pressure of a Liquid
● Introduced with Dalton's law, section 6.14.● Properly called equilibrium vapor pressure
of a liquid.● Increases with temperature.● Reason liquids in open containers (non
equilibrium situation) evaporate.
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The Vapor Pressure of a Liquid
Figure 8.11
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The Vapor Pressure of a Liquid
Figure 8.12
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The Vapor Pressure of a Liquid
Figure 8.13
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Melting Point and Freezing Point
● Should be the same.Some liquids supercool.
Solids don't superheat.● Melting points used to characterize
compounds.Purity
Identification, especially in organic chemistry
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Melting Point and Freezing Point
● During melting, heat added to the system does not raise the temperature.
● Where does it go?
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Melting Point and Freezing Point
● During melting, heat added to the system does not raise the temperature.
● Where does it go?Into ΔH°fus
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Melting Point and Freezing Point
Figure 8.15
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Boiling Point
● Indication of strength of intermolecular forces.
● Vapor pressure of liquid = external pressure.
Therefore, bp varies with external pressure.● When external pressure is 1 bar, the
boiling point is called the normal boiling point.
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Boiling Point
Figure 8.17
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Phase Diagrams
● Plot of equilibrium phase as a function of P and T.
● Axes often not linear.● Determined experimentally.
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Phase Diagrams
Figure 8.18
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Hydrogen Bonding and the Anomalous Properties of Water
● Water is a strange substance.Density decreases upon freezing.
Boiling point is high.
Specific heat is high.● Many of its strange properties are the
result of the hydrogen bonding present in water.
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Hydrogen Bonding and the Anomalous Properties of Water
● HF has a larger ΔEN, but fewer H per X.● NH3 has more H per X, but a smaller
ΔEN. ● H2O has just the right balance of H per X
and ΔEN to make it such an unusual molecule.
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Solutions: Like Dissolves Like
● Move from pure liquids to solutions.● Emphasis on solubility:
Important property in chemistry and biochemistry.
● Characterize solvents asPolar.
Nonpolar. ● This terminology was first used in section
4.17.
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Solutions: Like Dissolves Like
● Polarity of solvent will determine what kind of solutes dissolve in it.
● Hence the title of the section.
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Solutions: Like Dissolves Like
● Iodine molecules (I2) are bound to each other through van der Waals interactions.
Intermolecular force
● KMnO4 is made up of K+ and MnO4- ions
which are bound to each other through ionic bonding.
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Solutions: Like Dissolves Like
Table 8.6
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Solutions: Like Dissolves Like
Figure 8.24
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Hydrophilic and Hydrophobic Molecules
● HydrophilicExample: molecules which hydrogen bond.
Soluble ionic compounds.● Hydrophobic
Example: hydrocarbons, CxHy.
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Hydrophilic and Hydrophobic Molecules
● Portions of a single molecule can be hydrophilic and hydrophobic:
OH part of an alcohol is hydrophilic.
The alkyl part (CxHy) is hydrophobic.Table 8.7
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Hydrophilic and Hydrophobic Molecules
Table 8.8
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Soaps, Detergents, and Dry-Cleaning Agents
● Involve two fundamental principlesSolubility
Intermolecular interactions
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Soaps, Detergents, and Dry-Cleaning Agents
● “Dirt” is not soluble in water.● It is soluble in hydrocarbons, but no one
wants to wash their clothes with lighter fluid or gasoline.
● Trick the “dirt” into dissolving in a hydrocarbon which has been slipped into a water medium.
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Soaps, Detergents, and Dry-Cleaning Agents
● …a hydrocarbon which has been slipped into a water medium.
Figure 8.28
Figure 8.31
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Soaps, Detergents, and Dry-Cleaning Agents
● Major problem with soap: hard water
- 2+3 2 16 2 3 2 16 2 22CH (CH ) CO ( ) Ca ( ) Ca{CH (CH ) CO } ( )aq aq s
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Soaps, Detergents, and Dry-Cleaning Agents
● Water softening
● Synthetic soaps
Figure 8.32
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Why Do Some Solids Dissolve in Water?
● Both ionic and covalent solids will dissolve in water.
● But not all ionic and covalent solids!
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Why Do Some Solids Dissolve in Water?
● Energy required to break up solid.● Energy produced by interaction of solid
components with solvent.
The relative magnitude of these two energy terms determines solubility.
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Solubility Equilibria
● Already seen an equilibrium, section 8.5:liquid vapor.⇄
● Now we have pure solid solute in solution.⇄
● Reversible and dynamic in both cases.
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Solubility Equilibria
● Precipitation reactionSoluble species form an insoluble product.
● Saturated Solutionrate of precipitation = rate of dissolution
● SolubilityMaximum amount of solute which can be dissolved at a given temperature.
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Solubility Equilibria
● ElectrolytesStrong electrolytes
– All the solutes break up into ions.
Weak electrolytes– Some of the solutes break up into ions.
● Nonelectrolytes– None of the solutes break up into ions.
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Solubility Rules
Table 8.9
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Solubility Rules
● Solubility is a subjective term.
Figure 8.38
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Net Ionic Equations
● Condensed BaCl2(aq) +Na2SO4(aq) → BaSO4(s)↓ +2NaCl(aq)
● Ionic
Ba+2(aq) + 2Cl-(aq) + 2Na+(aq) + SO4-2(aq) →
BaSO4(s)↓ + 2Na+(aq) + 2Cl-(aq)
● Net Ionic
Ba+2(aq) + SO4-2(aq) → BaSO4(s)↓
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Net Ionic Equations
● Each of the previous three types has its virtues and limitations.
● For example, the net ionic lacks information about the spectator ions:
Ba+2(aq) + SO4-2(aq) → BaSO4(s)↓