OCR Gateway GCSE Chemistry

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3.3.1 Oxidation & Reduction

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Oxidation & Reduction

  • Oxidation and reduction involve the addition or removal of oxygen from a substance
  • Oxidation is a reaction in which:
    • Oxygen is added to an element or a compound

  • Reduction is a reaction in which:
    • Oxygen is removed from an element or a compound
  • A redox reaction is one where oxidation and reduction are both taking place at the same time
  • In the following reaction:

ZnO + C ⟶ Zn + CO 

    • The carbon atom has been oxidised since it has gained oxygen
    • The zinc oxide has been reduced since it has lost oxygen
    • This is an example of a redox reaction as oxidation and reduction are both taking place
    • Carbon is known as a reducing agent as it has reduced another substance (the zinc oxide)
    • Zinc oxide is known as an oxidising agent as it has oxidised another substance (the carbon) 

Worked example

 Magnesium reacts with zinc oxide:

Magnesium + zinc oxide → magnesium oxide + zinc 

Explain which substance is reduced and which substance acts as a reducing agent 

Answer:

    • Zinc oxide is reduced because it loses oxygen
    • Magnesium acts as the reducing agent as it reduces the zinc oxide 

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