Chapter 12: Solutions and other complex forces

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Chapter 12 Solutions and other complex forces

• Many of the forces weve talked about occur
  between ions/molecules in solutions
• Definition A homogeneous mixture (only one
  phase)
• Examples saltwater, tap water, gemstones,
  brass, air
• Made up of a solvent and a solute Solvent the
  substance present in the larger amount.
• Solute the other substance
• Dissolving depends on attractive forces and
  entropy

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What well cover

• Definitions
• Control of Solubility
• Things that affect solubility
• Concentration units
• Colligative properties

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Part 1 Definitions

• There is a maximum amount of any solute that will
  dissolve in a given solvent
• If less than the maximum has been added, solution
  is unsaturatedIf the max or more than the max
  has been added, solution is saturatedCan also
  have Supersaturated solutions
• The concentration of a solution is the amount of
  solute that has been dissolved in a solvent.
• Many units of concentrationmolarity (mol/L),
  weight (g/g), ppm (mg/L)

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Solubility

• If a solute will dissolve in a solvent, it is
  soluble.
• Some solutes have limits,
• some are infinitely soluble in a
  solvent.
• Sugar 200 g in 100 mL water at 20
  ºCEthanol infinitely soluble in waterGases
  are infinitely soluble in one another

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Trends and Control of Solubility
For now, we are examining molecular compounds-
not ionic compounds.
General rules 1. polar solutes dissolve in
polar solvents 2. nonpolar solutes dissolve in
nonpolar solvents Like dissolves Like Oil
and water dont mix is oil polar or
nonpolar? You try which of these will dissolve
in water? CH3OH CH3CH3 NH3
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Introduction to Thermodynamic Control of the
World
Enthalpy, ?H Stronger bonds/IMFs are favored
over weak ones. Entropy, ?S Freedom of
movement is favored over constrained states.
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Trends and Control of Solubility and Mixing Why
do some things mix and others do not?
What controls Solubility Enthalpy (enthalpy
of solution) Negative if new forces are
stronger than original forces Entropy Depends
on the entropy change of both the water and the
solute.
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Effects of Polarity
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Why do Proteins Fold?
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Without lipids, youd fall apart.
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What holds DNA together?
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DNA, H-Bonding, and Entropy
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Introduction to Polymers
Polymers are long molecules made of repeating
units, called monomers.
In general
Specific example
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Forces between polymer chains Crosslinks
Weak Intermolecular force crosslinks
Strong Colvalent bond crosslinks
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Laundry!
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Part 2 External Control of Solubility Temperatur
e and Pressure
Predictions Will solubility increase or
decrease with increasing temperature? Will
solubility of a gas increase or decrease with
increasing pressure?
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