Redox & Disproportionation (Edexcel AS Chemistry)

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Disproportionation

Disproportionation reactions

  • A disproportionation reaction is a reaction in which the same species is simultaneously oxidised and reduced

 Electrochemistry Disproportion Reaction, downloadable AS & A Level Chemistry revision notes

Example of a disproportion reaction in which the same species (chlorine in this case) has been both oxidised and reduced

Worked example

Using Oxidation Numbers

Balancing disproportionation reactions

Balance the disproportionation reaction which takes place when chlorine is added to hot concentrated aqueous sodium hydroxide. The products are Cl- and ClO3- ions and water

Answer

Step 1: Write the unbalanced equation and identify the atoms that change in oxidation number:

Electrochemistry Step 1 Balancing disproportionation reactions, downloadable AS & A Level Chemistry revision notes

Step 2: Deduce the oxidation number changes:

Electrochemistry Step 2 Balancing disproportionation reactions, downloadable AS & A Level Chemistry revision notes

Step 3: Balance the oxidation number changes:

Electrochemistry Step 3 Balancing disproportionation reactions, downloadable AS & A Level Chemistry revision notes

Step 4: Balance the charges

Electrochemistry Step 4 Balancing disproportionation reactions, downloadable AS & A Level Chemistry revision notes

Step 5: Balance the atoms

Electrochemistry Step 5 Balancing disproportionation reactions, downloadable AS & A Level Chemistry revision notes

Worked example

Oxidation and reduction

In each of the following equations, state which reactant has been oxidised and which has been reduced.

  1. Na++ Cl- →  NaCl
  2. Mg + Fe2+  →  Mg2+ + Fe
  3. CO + Ag2O  →  2Ag + CO2

Answer 1:

    • Oxidised: Cl- as the oxidation state has increased by 1
    • Reduced: Na+ as the oxidation state has decreased by 1

Answer 2:

    • Oxidised: Mg as the oxidation state has increased by 2
    • Reduced: Fe2+ as the oxidation state has decreased by 2

Answer 3:

    • Oxidised: C as it has gained oxygen
    • Reduced: Ag as it has lost oxygen

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Philippa

Author: Philippa

Expertise: Chemistry

Philippa has worked as a GCSE and A level chemistry teacher and tutor for over thirteen years. She studied chemistry and sport science at Loughborough University graduating in 2007 having also completed her PGCE in science. Throughout her time as a teacher she was incharge of a boarding house for five years and coached many teams in a variety of sports. When not producing resources with the chemistry team, Philippa enjoys being active outside with her young family and is a very keen gardener.