Oxidation & Reduction (CIE IGCSE Chemistry)
Revision Note
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Chemistry
Oxidation & Reduction
Redox reactions
- Oxidation and reduction take place together at the same time in the same reaction
- These are called redox reactions
- 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 compound
Example: Identifying the loss and gain of oxygen in an equation
zinc oxide + carbon → zinc + carbon monoxide
ZnO + C → Zn + CO
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- In this reaction, the zinc oxide has been reduced since it has lost oxygen
- The carbon atom has been oxidised since it has gained oxygen
Names using oxidation numbers
- Transition elements can bond in different ways by forming ions with different charges
- When naming, the charge on the ion is shown by using a Roman numeral after the element's name
- e.g. iron can form ions with a 2+ charge, called iron(II) ions or a 3+ charge, called iron(III) ions
- The Roman numeral is the oxidation number of the element
- When iron reacts with oxygen to form iron oxide, the formula depends on the oxidation state of the iron ions
- The compound where iron has a 2+ charge has the formula FeO and is called iron(II) oxide
- The compound where iron has a 3+ charge has the formula Fe2O3 and is called iron(III) oxide
Exam 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.
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