REDOX

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REDOX

• Oxidation-Reduction Reactions

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Oxidation-Reduction Reactions

• Electrons are transferred from 1 atom to another.
• All single-replacement combustion rxns are
  redox rxns.

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Oxidation

• loss of electrons.
• LOSS of ELECTRONS OXIDATION
• LEO

4
Reduction

• gain of electrons.
• GAIN of ELECTRONS REDUCTION
• GER

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REDOX

• Oxidation Reduction are complementary.
• They occur together simultaneously or not at
  all.

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LEO GOES GER!!!
Memorize!
Oxidation of Cu
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Oxidation Numbers

• In Ionic Compounds the number of electrons lost
  or gained by an atom when it forms ions.

Oxidation states of Vanadium
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Assigning Oxidation Numbers
8 RULES
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8 Rules for Oxidation Numbers

• of a free, uncombined element 0.

1.
Na He O2 N2 S8 Cl2 P
of a monatomic ion charge on ion.
2.
Ca2 2. Cl-1 -1. Al3 3.
Remember Ions occur in ionic compounds CaCl2,
Al(NO3)3, etc.
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8 Rules for Oxidation Numbers
3.

• Fluorine is always -1.

CF4
4.
Hydrogen is nearly always 1, except when its
bonded to a metal. Then its -1.
LiH CaH2 NaH
H2O, HNO3, H2SO4
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8 Rules for Oxidation Numbers
Oxygen is nearly always -2 except when its
5.
OF2
-Bonded to fluorine, where O is 2
O22-
-In the peroxide ion, where O is -1.
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8 Rules for Oxidation Numbers
The sum of oxidation numbers in a neutral
compound is 0.
6.
H2O CO2 NO SO3
The sum of oxidation numbers in a polyatomic ion
charge of the ion.
7.
Sum in SO42- -2. Sum in NO3- -1.
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8 Rules for Oxidation Numbers
8.
In covalent compounds, the oxidation number of
the more electronegative atom is the negative
charge it would have if it was an ion.
NH3 N -3, H 1.
SiCl4 Si 4, Cl -1.
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Assign Oxidation Nos

• KCl
• CaBr2
• CO
• CO2
• Al(NO3)3
• Na3PO4
• H2S
• NH41
• SO3-2

K 1, Cl -1
Ca 2, Br -1
C 2, O -2
C 4, O -2
Al 3, O -2, N 5
Na 1, O -2, P 5
H 1, S -2
N -3, H 1
S 4, O -2
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Electrons are Negative!

• Why do we use the word reduced when electrons
  are gained?

Look at how the oxidation number changes. For
example, if Cl gains an electron it becomes Cl-1.
The oxidation number decreased from 0 to -1.
The oxidation number was reduced.
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Writing Equations

• Even though oxidation reduction occur together,
  we can write separate equations for each process.
• Called Half-Reactions.
• In order to balance a redox equation, we have to
  split the full equaton into half-reactions.

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Conservation of Mass

• of atoms of each type is the same on both sides
  of the equation.
• Still holds for half-reactions.
• Do this step first.

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Conservation of Charge

• Total charge on LHS must equal total charge on
  RHS.
• In the past, we usually had both sides neutral.
  (0 0.)
• Note Total charge can be nonzero. Just has to
  be equal on the 2 sides.
• If not balanced, add electrons to whichever side
  is too positive.

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Reduction Half-Reactions
Electrons are gained so they are like a reactant!

• I2 2e- ? 2I-
• O2 4e- ? 2O-2
• Half-reactions must demonstrate conservation of
  mass conservation of charge.
• of atoms of each element on LHS equals
  RHS.
• Total charge on LHS Total charge on RHS

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Oxidation Half-reactions
Electrons are lost so they appear on the product
side!

• K ? K1 1e-
• Fe2 ? Fe3 1e-
• Cu ? Cu2 2e-
• Total Charge on LHS Total Charge on RHS
• atoms LHS atoms RHS

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Identifying Half-Reactions

• Reduction electron term is on reactant side.
• Oxidation electron term is on product side.

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Vocabulary Interlude

• Oxidizing Agent Is itself reduced. Accepts
  electrons from something else aids oxidation
  for another species.
• Reducing Agent Is itself oxidized.
• Loses electrons to something else aids
  reduction for another species.

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Figuring out what is what!

• Given an unbalanced equation.
• Goal Balance it.
• Procedure
• Have to split it into half-reactions
• Balance them separately
• Make the electrons even
• Add them together

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Whats oxidized whats reduced?

• USE OIL RIG

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4 3 2 1 0 -1 -2 -3 -4
2) And if youre lucky you strike oil it
shoots up
OIL RIG
1) You dig down with an oil rig
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Oxidizing Reducing Agents

• They are both ALWAYS on the reactant side.
• Identify them by seeing how the oxidation numbers
  change.
• Mg Cu2 ? Mg2 Cu

4 3 2 1 0 -1 -2 -3 -4
0
0
2
2
OIL RIG
Mg is oxidized, so Mg is the reducing agent!
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Oxidizing Reducing Agents

• Whats oxidized whats reduced
• Ca FeCl2 ? CaCl2 Fe
• Assign oxidation numbers
• Figure out what increases what decreases.

2, -1
0
2, -1
0
4 3 2 1 0 -1 -2 -3 -4
OIL RIG
Ca is oxidized Fe2 is reduced.
Ca reducing agent FeCl2 oxidizing agnt.
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Oxidizing Reducing Agents
4, -1

• 2 FeBr3 SnBr2 ? 2 FeBr2 SnBr4
• Fe3 is reduced to Fe2
• Sn2 is oxidized to Sn4
• FeBr3 is the oxidizing agent.
• SnBr2 is the reducing agent.

3, -1
2, -1
2, -1