Natural Science

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Natural Science

• Chapter 5 6
• Spring 2006

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• Acids and Bases

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Acids

• Sharp sour taste
• Compounds that can donate a hydrogen ion (H) in
  reactions
• HCl H2O gt H3O Cl-

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Strong Acids

• Completely ionize in water to hydronium ion (H)
  and an anion
• Examples (Mineral acids)
• Hydrochloric acid (Muriatic acid) HCl
• Hydrobromic acid HBr
• Sulfuric acid (Oil of vitrol) H2SO4
• Nitric acid HNO3

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Weak acids

• Acids that do not completely ionize in water
• HOAc ltgt H OAc-
• Examples
• Acetic acid (Vinegar) HO2CCH3
• Hydrofluoric acid HF
• Phosphoric acid H3PO4
• Ascorbic acid (Vitamin C)

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Strength and concentration

• A strong acid (complete ionization) can be dilute
  or concentrated in solution
• A weak acid (incomplete ionization) can be dilute
  or concentrated in solution
• Strength is a chemical property
• Concentration is a physical property

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Bases

• Bitter taste, slippery to feel
• Compounds that ionize to give hydroxide (OH-) ion
  in water, compounds that can donate a hydroxide
  ion
• NaOH gt Na OH-
• Compounds that can accept a hydrogen ion
• NH3 H gt NH4

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Strong bases

• Compounds that react completely with water to
  generate hydroxide ion
• Examples
• Sodium hydroxide NaOH
• Potassium hydroxide KOH
• Sodium oxide Na2O
• Barium hydroxide Ba(OH)2

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Weak bases

• Compounds that do not completely react with water
  to form hydroxide
• Examples
• Ammonia NH3
• Magnesium oxide (MOM) MgO
• Organic alkaloids (Nitrogen containing organic
  molecules) cocaine, barbituates, caffeine, heroin

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pH

• pH is a scale of the amount of acid or base in a
  solution
• Based on the self-ionization of water2H2O ltgt
  H3O OH-
• Hydronium ion and hydroxide ion concentration are
  always linked to each other through the water
  constant
• H3OOH- 1 x 10-14

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pH Definition and Scale

• pH -logH3O
• Normal range of scale runs from 0 to 14
• Although larger and smaller numbers are
  sometimes used they are not very meaningful
• A value of 7 is called neutral, the amount of
  hydronium and hydroxide is equal

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pH values

• Values less than 7 are due to increasing amounts
  of hydronium ion (Acid)
• Values greater than 7 are due to increasing
  amounts of hydroxide ion (Base)
• A difference of 1 on the pH scale means a
  difference in concentration of hydronium ion by a
  factor of 10

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Acid-Base Reactions

• Acid Base gt Salt water
• NaOH HCl gt NaCl H2O
• As an acid-base reaction goes forward, the pH
  changes. This can be used to determine the
  amount of acid or base in solution by monitoring
  the pH. These are called acid-base titrations.

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Common Reactions

• Vinegar Baking soda --gt sodium acetate
  carbon dioxide water
• MOM Stomach acid (HCl)
• Tannic Acid Lime --gt lawn pH adjustment

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• Reduction-oxidation Reactions

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Reduction

• An ancient term from metallurgy where an ore of a
  metal, such as mercury sulfide (cinnabar) is
  reduced to the element. In modern chemical terms
  this is a gain in electrons, but we still use the
  term reduction.
• Hg2S 2e- gt Hgo

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Oxidation

• Oxidation is also an ancient term and refers to
  the reaction of oxygen with substances
• The sulfide in mercury sulfide undergoes
  oxidation in that it loses electrons
• S-2 gt S4 6e-

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Reduction and Oxidation

• In reactions these processes are always connected
  to each other as free electrons are not created.
  
• The term Redox is used to describe these
  reactions and emphasizes the relation
• Many important processes are redox reactions

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Combustion Reactions

• CH4 2O2 gt CO2 2H2O
• Oxidation half-reactionC-4 gt C4 8e-
• Reduction half-reactionOo 2e- gt O-2

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Fuel Cells

• Separate combustion reaction into two parts, and
  use the electrons as they flow through an
  electrical connection to do work.
• 2H2 O2 gt 2H2O
• ReductionOo 2e- gt O-2
• OxidationHo gt H e-

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Fuel Cell
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Metal Displacement

• CuSO4 Zn gt Cu ZnSO4
• Reduction half-reactionCu2 2e- gt Cuo
• Oxidation half-reactionZno gt Zn2 2e-
• Activity Series

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Rechargeable batteries

• Lead-acid battery
• Pb PbO2 2H2SO4 ltgt 2PbSO4 2H2O
• Pbo ltgt Pb2 2e-
• Pb4 2e- ltgt Pb2

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Lead Acid Battery
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Halogen Displacement

• 2NaBr Cl2 gt Br2 2NaCl
• ReductionClo e- gt Cl-
• OxidationBr- gt Bro e-
• F2 gt Cl2 gt Br2 gt I2

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Corrosion

• 4Fe 3O2 gt 2Fe2O3
• ReductionOo 2e- gt O-2
• OxidationFeo gt Fe3 3e-
• Activity Series zinc corrodes before iron
  (sacrificial electrode)

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