Chapter 14: Solutions

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Chapter 14 Solutions

• 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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Solutions

• 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 saturated
• 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
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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Trends and Control of Solubility
What controls Solubility Enthalpy (enthalpy
of solution) negative if new forces are
stronger than original forces Entropy more
complicated
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Forcing Solubility

• How do you make something dissolve if it is
  normally insoluble in a solvent?
• Grease and grime are made up of nonpolar
  compounds. Will they dissolve in water?
• They will dissolve in nonpolar solvents, like
  turpentine, gasoline. Good for cleaning hands?
• Soap the substance that makes nonpolar
  compounds dissolve in water. How would you
  design a soap molecule? What chemical properties
  should it have?

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Soap and Detergent

• Soap is both polar and nonpolarAttracted to
  water (polar) and grime (nonpolar)Soap is the
  salt of a fatty acid, it is a surfactant molecule.

hydrophobic end hydrophilic end
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Soap

• Soap is both polar and nonpolarAttracted to
  water (polar) and grime (nonpolar)
• Made from fats, which contain 3 fatty acids and
  glycerol

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Soap

• Nonpolar end is attracted to grimePolar end is
  attracted to waterDirt is picked up off
  clothes, skin, and rinsed away

See Soap movie
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Soap

• Hard water and soap
• Hard water contains high concentration ofCa2
  and Mg2 ions
• Ion-ion forces between Ca2, Mg2 and soap anion
  results in soap scum (soap forms a solid compound
  on your skin, bathtub, etc.)
• Water softeners replace Ca2, Mg2 with Na
• How does dry-cleaning work? Previously used
  CCl4, now less carcinogenic solvents

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Fabric Softener Cationic Surfactants
without
with
What effect will softener use have on
absorptivity?
without
with
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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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Cotton
Cellulose polymer
Absorbs water. Cellulose chains
crosslinked by H-bonding.
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Wrinkling
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Permanent Press Cotton
Chemical crosslinking agent.