chapter 8 liquids and solutions
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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. Chapter 8 Liquids and Solutions. The Structure of Gases, Liquids and Solids. Figure 8.1. - PowerPoint PPT PresentationTRANSCRIPT
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.
The Structure of Gases, Liquids and Solids
Figure 8.1
The Structure of Gases, Liquids and Solids
Table 8.1
The Structure of Gases, Liquids and Solids
● Intramolecular bond● Intermolecular force
Figure 8.2
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.
Intermolecular Forces
Five important types
dipole-dipole
dipole-induced dipole
induced dipole-induced dipole
van der Waals (aka London, dispersion)
Hydrogen bonding
Intermolecular Forces
● dipole-dipole
Figure 8.3
Intermolecular Forces
● dipole-induced dipole
Figure 8.4
Intermolecular Forces
● induced dipole-induced dipole
Figure 8.5
Intermolecular Forces
● van der WaalsWeak
Present in all systems.
Proportional to the number of electrons in the molecules.
Table 8.2
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
Intermolecular Forces
● Hydrogen bondingMisleading name
Possible in molecules with H - X bond where X is F, O, or N.
– Highlights importance of Lewis structure.
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.
Intermolecular Forces
● Hydrogen bondingProfound consequences
Figure 8.9
Intermolecular Forces
● Hydrogen bonding
...results in liquid water on Earth!!
Relative Strengths of Intermolecular Forces
Table 8.3
Relative Strengths of Intermolecular Forces
Table 8.5
The Kinetic Theory of Liquids
● Average KE T (section 6.2).● Range of KE.● Intermolecular forces present.
That's why it's a liquid.
The Kinetic Theory of Liquids
● Enthalpy of vaporization, ΔH°vap.
● Enthalpy of fusion, ΔH°fus.
● ΔH°vap >> ΔH°fus.
Why?
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.
The Vapor Pressure of a Liquid
Figure 8.11
The Vapor Pressure of a Liquid
Figure 8.12
The Vapor Pressure of a Liquid
Figure 8.13
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
Melting Point and Freezing Point
● During melting, heat added to the system does not raise the temperature.
● Where does it go?
Melting Point and Freezing Point
● During melting, heat added to the system does not raise the temperature.
● Where does it go?Into ΔH°fus
Melting Point and Freezing Point
Figure 8.15
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.
Boiling Point
Figure 8.17
Phase Diagrams
● Plot of equilibrium phase as a function of P and T.
● Axes often not linear.● Determined experimentally.
Phase Diagrams
Figure 8.18
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.
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.
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.
Solutions: Like Dissolves Like
● Polarity of solvent will determine what kind of solutes dissolve in it.
● Hence the title of the section.
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.
Solutions: Like Dissolves Like
Table 8.6
Solutions: Like Dissolves Like
Figure 8.24
Hydrophilic and Hydrophobic Molecules
● HydrophilicExample: molecules which hydrogen bond.
Soluble ionic compounds.● Hydrophobic
Example: hydrocarbons, CxHy.
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
Hydrophilic and Hydrophobic Molecules
Table 8.8
Soaps, Detergents, and Dry-Cleaning Agents
● Involve two fundamental principlesSolubility
Intermolecular interactions
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.
Soaps, Detergents, and Dry-Cleaning Agents
● …a hydrocarbon which has been slipped into a water medium.
Figure 8.28
Figure 8.31
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
Soaps, Detergents, and Dry-Cleaning Agents
● Water softening
● Synthetic soaps
Figure 8.32
Why Do Some Solids Dissolve in Water?
● Both ionic and covalent solids will dissolve in water.
● But not all ionic and covalent solids!
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.
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.
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.
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.
Solubility Rules
Table 8.9
Solubility Rules
● Solubility is a subjective term.
Figure 8.38
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)↓
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)↓