Reduction - Oxidation

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Reduction - Oxidation

• Chapters 20 21

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Oxidation Numbers (States)

• Positive, negative or neutral values assigned to
  an atom to keep track of the number of electrons
  lost or gained.

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Oxidation Number Rules

• Elements alone 0
• Example Cu, N2
• Monatomic ion charge
• Example Cl-
• Compound S 0
• Example H2O
• Polyatomic ion S charge
• Example NO3-

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Common Oxidation Numbers

• Group 1? 1
• Group 2 ? 2
• Group 13 ? 3
• Group 15 ? -3
• Group 16 ? -2
• Group 17 ? -1
• Some exceptions to each above

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Redox Reactions

• Reduction Oxidation, or redox, involves the
  transfer of electrons
• Reduction gain of electrons
• Oxidation loss of electrons

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Redox Reactions

• LEO goes GER
• Lose Electrons Oxidation
• Gain Electrons Reduction

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Redox Reaction
0
0
-1
2

• Mg Cl2 ? MgCl2
• Mg - lost electrons (oxidation)
• Cl gained electrons (reduction)

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Redox Reaction

• Zn CuSO4 ? Cu ZnSO4
• One element loses electrons (oxidation)
• One element gains electrons (reduction)
• All other ions are spectators

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Net Ionic Equation

• Shows only the ions involved in the redox
  reaction, not spectator ions
• Still shows conservation of mass and charge
• Zn CuSO4 ? Cu ZnSO4
• Zn Cu2 ? Cu Zn2

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Net Ionic Example

• Zn 2HCl ? H2 ZnCl2
• Zn 2H ? H2 Zn2

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Half Reactions

• Only shows one element and how many electrons are
  gained or lost
• Zn CuSO4 ? Cu ZnSO4
• Zn Cu2 ? Cu Zn2 (Net Ionic)
• Zn ? Zn2 2e- Oxidation
• Cu2 2e- ? Cu Reduction

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Oxidation

• Loss of Electrons
• Examples
• Zn ? Zn2 2e-
• 2Cl- ? Cl2 2e-

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Reduction

• Gain of electrons
• Examples
• Ag e- ? Ag
• Cl2 2e- ? 2Cl-

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Balancing Reactions

• The number of electrons lost must equal the
  number of electrons gained
• Example
• Zn Na2SO4 ? 2Na ZnSO4
• Zn ? Zn2 2e-
• 2(Na e- ? Na)

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Spontaneous Reactions

• More active element does not want to be alone
• Table J
• Metal being oxidized must be ABOVE metal being
  reduced for spontaneous reactions to occur
• Reversed for Nonmetals

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Spontaneous Reactions

• Examples
• Zn CuSO4 ? Cu ZnSO4
• CaSO4 Mg ? Ca MgSO4
• Zn 2HCl ? H2 ZnCl2
• F2 2NaI ? I2 2NaF

YES
NO
YES
YES
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Electrochemical Cells

• any device that converts chemical energy into
  electrical energy or electrical energy into
  chemical energy
• Two types
• Voltaic (Chemical)
• Electrolytic

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Electrochemical Cells

• Electrode conductor in an electrical circuit
  that carries electrons to or from a substance
  other than a metal.
• Cathode electrode where reduction takes place
• Anode electrode where oxidation takes place

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Voltaic Cell

• Flow of electrons is spontaneous based on
  electronegativity and ionization energy
• Chemical energy is converted to electrical energy
• Cathode is positive, anode is negative
• Examples Batteries

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Voltaic Cell
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Electrochemical Cell Components

• Salt Bridge
• Allows for the passage of ions, not electrons
• Switch
• Device that opens(turns off) and closes(turns on)
  circuit

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Voltaic Cell
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Electrolysis

• Process in which electrical energy is converted
  to chemical energy
• Example
• 2H2O ? 2H2 O2

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Electrolytic Cells

• Electrons are pushed by an outside power source
• Electrical energy is converted to chemical energy
• Examples Electroplating, Electropolishing

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Electrolytic Cell
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Voltaic Cell
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Electrolytic Cell
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Voltaic or Electrolytic?
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Voltaic or Electrolytic?