Oxidation & reduction
What is a redox reaction?
- A redox reaction is where oxidation and reduction take place together at the same time in the same reaction
- In terms of oxygen:
- Oxidation is where oxygen is added to an element or a compound
- Reduction is where oxygen is removed from an element or compound
- The reaction between zinc oxide and carbon is an example of a redox reaction
- Zinc oxide is reduced because it has lost oxygen
- Carbon is oxidised because it has gained oxygen
Both reduction and oxidation has occurred in this reaction so it is classed as a redox reaction
Worked example
Explain which chemicals that are reduced and oxidised in the reaction between iron(III) oxide and carbon.
iron(III) oxide + carbon monoxide → iron + carbon dioxide
Fe2O3 + 3CO → 2Fe + 3CO2
Answer:
- Iron(III) oxide loses oxygen, so it is reduced
- Carbon monoxide gains oxygen, so it is oxidised
Examiner Tip
You may see the term oxidation state used instead of oxidation number.
Although there is a subtle difference between the two terms (this is beyond the scope of this course), they are often used interchangeably.
Usually oxidation number is used to refer to the Roman numerals found within the name.
