Redox Reactions

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Redox Reactions
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Chemical Reactions

• There are 3 major classes of chemical reaction
• 1. Precipitation
• 2. Acid-base
• 3. Redox

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Oxidation

• Refers to the gain of oxygen in a chemical
  reaction
• EXAMPLE
• Iron oxygen

Iron(II) oxide
Write the chemical equation (unbalanced)
The iron has gained oxygen and has been oxidised
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Reduction

• Is the opposite of oxidation
• This means that it involves the lose of oxygen

Write a chemical equation for the reduction of
calcium oxide. Balance the equation
CaO Ca O2
2
2
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Redox reactions
Whenever a chemical is oxidised, another chemical
must be reduced, and vise vera EXAMPLE
Mg CuO MgO Cu

• Write a similar equation for the reaction of zinc
  and iron oxide.
• Label the oxidation and reaction steps

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Introducing electrons

• Mg CuO MgO Cu
• The oxidation and reduction steps can be written
  out separately
• Mg MgO
• CuO Cu

Mg2O2-
OXIDATION
REDUCTION
Cu2O2-
Re-write the above two steps, but add charges to
the ions involved
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• In the oxidation step
• Mg O2 Mg2O2-
• The magnesium atoms have turned into magnesium
  ions
• Have they gained or lost electrons?
• OXIDATION IS ALWAYS LOSS of electrons
• O.I.L.
• Where have the electrons gone to?

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• They have been taken by the copper
• Cu2O2- Cu
• The copper has turned from ions into atoms

REDUCTION IS ALWAYS GAIN of electrons R.I.G.
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Practice

• Write similar ion-electron equations for
• Calcium ions turning into calcium atoms
• Sodium ions turning into sodium atoms
• Aluminium ions turning into aluminium atoms
• Potassium atoms turning into potassium ions
• Nickel atoms turning into nickel(II) ions

All of these REDUCTIONS can be found in the data
booklet
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Writing ion-electron equations

• All reductions are found in data booklet
• To write the oxidation, reverse the equation

Cu2 2e Cu
Cu Cu2 2e

• Both sides of the equation should be neutral
  when the charges are added together
• REMEMBER OIL RIG

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Problems

• Look at the following equation
• Zn Ag2O ZnO
  Ag
• Which chemical is being oxidised?
• Write an ion-electron equation for the oxidation
  step.
• Write an ion-electron equation for the reduction
  step.
• 2. Assessment tests 10.3 and 10.4