Ch. 4 ReDox yes we can do this

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Ch. 4 Re-Dox yes we can do this
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ReDox Reactions a reaction in which one or more
electrons are transferred

• You must be able to assign oxidation numbers to
  ions in ionic compounds
• Rules
• Oxidation states of an atom in an element is
  0.
• Oxidation state of a monatomic ions is the
  same
• as its charge. Cl1- ion is -1
• Fluorine in a compound is always an oxidation
  
• state of -1
• Oxygen is usually assigned an oxidation state
  of
• -2 Exception Hydrogen peroxide H2O2
  (-1) and
• in OF2 (2)
• In a covalent compound hydrogen is assigned a
  1
• The sum of the oxidation states must be zero
  for electrically neutral compounds For an Ion,
  the sum must equal the charge

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Example

• Assign Oxidation states to each of the following
• CO2
• O -2 2(-2) ____ 0
• C must equal 4
• SF6
• F 6(-1) ____ 0
• S must 6
• NO3-
• O -2 3(-2) ____ -1
• N must equal 5

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LEO the lion goes GER Loss of electrons
oxidation Gain of electrons reduction

• Which is oxidized and which is reduced?
• 2Na Cl2 ? 2NaCl
• 0 0 1 -1
• Sodium is oxidized because its oxidation number
  increased Chlorine is reduced because its
  oxidation number decreased
• CH4 2O2 ? CO2 2H2O
• -4 1 0 4 -2 1 -2
• Carbon is oxidized because its oxidation number
  increased Oxygen is reduced because its
  oxidation number decreased

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Redox Practice Which is reduced? Which is
Oxidized? Which is the reducing Agent? Which is
the oxidizing agent?

• 2H2 g O2 g? 2H2O
• Zn (s) Cu2 (aq)? Zn2(aq) Cu (s)
• 2AgCl(s) H2(g) ? 2H(aq) 2Ag(s) 2Cl- (aq)
• 2MnO4- 16H 5C2O42- ? 2 Mn2 10CO2 8 H2O
• 2H2 O2 ? 2H2O
• 0 0 H1 O 2-
• H is oxidized O is reduced oxidizing agent O2
  reducing agentH2

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Zn (s) Cu2 (aq)? Zn2(aq) Cu (s)0 2
2 0Zinc is oxidized Cu is reduced Zinc is
the reducing agent Copper is the oxidizing agent

• 2AgCl(s) H2(g) ? 2H(aq) 2Ag(s) 2Cl- (aq)
• 1 1- 0 1
  0 1-
• Hydrogen is oxidized by silver chloride
  (oxidizing agent)
• Silver is reduced by hydrogen gas (reducing
  agent)
• 2MnO4- 16H 5C2O42- ? 2 Mn2 10CO2 8 H2O
• 72- 1 32- 2 42- 12-
• manganese is reduced by oxalate ion (reducing
  agent)
• carbon is oxidized by permanganate ion
  (oxidizing agent)

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Balancing Redox Equations using the half reaction
method

• 1. Write each half reaction
• Cu (s) HNO3 (aq) ? Cu2 (aq) NO (g)
• 0 15 2
  2-2
• Copper is oxidized Cu ? Cu2
• Nitrogen is reduced HNO3 ? NO
• 2. Balance each reaction electrically
  Cu ? Cu2 2e-
• HNO3 ? NO already electrically balanced

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Next Balance all atoms that are neither oxygen
nor hydrogen

• Balance oxygens by adding water to the side that
  needs oxygen
• HNO3 ? NO 2H2O
• Balance hydrogens by adding H to the side that
  needs them
• HNO3 3H ? NO 2H2O
• Balance Charges if needed
• HNO3 3H 3e- ? NO 2H2O

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Equalize electrons by finding the lowest common
denominator and multiplying the reduction and
oxidation accordingly

• 2HNO3 6H 6e- ? 2NO 4H2O
• 3Cu ? 3Cu2 6e-
• Add the reactants and products and cancel any
  duplicates on both sides
• 2HNO3 6H 3Cu ? 2NO 4H2O 3Cu2

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OK that was in acidic solutions, what about in a
basic solution?

• Balance it as if it were in acidic solution
  first.
• Because it is basic you must get rid of the
  excess H ion by adding OH- ions equal numbers
  on both sides.
• 2HNO3 6H3Cu 6OH-? 2NO 4H2O 3Cu2 6OH-
• H combines with OH- to make water
• 2HNO3 6H2O 3Cu ? 2NO 4H2O 3Cu2
• Cancel matching numbers of water out
• 2HNO3 2H2O 3Cu ? 2NO 3Cu2

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Problems due Thursday show all work

• From your Chemistry Study Guide pages 110-111
  50-57
• pages 113-114 83-88
• The End!
• Test Tuesday, Sept. 26th.
• Read Ch. 6 notes due next Friday Sept. 29th