Oxidation and Reduction in Term of Changes of Oxidation State

  • Oxidation involves an increase in oxidation state
  • Reduction involves a decrease in oxidation state
  1. Another way to determine oxidation and reduction is to see the change of the oxidation state after a reaction.
  2. An atom is said to be oxidised when its oxidation state increases.
  3. An atom is said to be reduced when its oxidation state decreases.

Example:
  1. The magnesium's oxidation state has increased by 2, from 0 to +2. Therefore, it has been oxidised.
  2. The hydrogen's oxidation state has decreased by 1, from +1 to 0. Therefore it has been reduced.
  3. The chlorine is in the same oxidation state on both sides of the equation - it hasn't been oxidised nor reduced.

Example:




There is no change of oxidation state for all elements. This isn't a redox reaction.



Example:
 

  1. In this example, we can see that the oxidation state of chlorine has increased and also decreased.
  2. Chlorine is oxidised and reduced, at the same time.
  3. This is a good example of a disproportionation reaction. A disproportionation reaction is one in which a single substance is both oxidised and reduced.




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