Classifying Oxides (CIE IGCSE Chemistry: Co-ordinated Sciences (Double Award))

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Classifying oxides

What are oxides?

  • Oxides are compounds made from one or more atoms of oxygen combined with one other element
  • Examples of oxides include: MgO, ZnO, K2O, CO2, SO2, H2O
  • Oxides can be classified based on their acid-base characteristics

Acidic oxides

  • Acidic oxides are formed when a non-metal element combines with oxygen
  • They react with bases to form a salt and water
  • When dissolved in water they produce an acidic solution with a low pH
  • Common examples include CO2, SO2, NO2 and SiO2

Basic oxides

  • Basic oxides are formed when a metal element combines with oxygen
  • They react with acids to form a salt and water
  • When dissolved in water they produce a basic solution with a high pH
  • Common examples include CuO and CaO

Basic and acidic oxides 

Metals, non-metals & metalloids in Periodic Table, IGCSE & GCSE Chemistry revision notesMetals form basic oxides while non-metals form acidic oxides

Amphoteric oxides

Extended tier only 

Neutral oxides

  • Some oxides do not react with either acids or bases and thus are said to be neutral
  • Examples include N2O, NO and CO

Amphoteric oxides

  • Amphoteric oxides are a curious group of oxides that can behave as both acidic and basic, depending on whether the other reactant is an acid or a base
  • In both cases salt and water are formed
  • Two of the most common amphoteric oxides are zinc oxide, ZnO and aluminium oxide, Al2O3
  • The hydroxides of both of these elements also behave amphoterically
  • Example of aluminium oxide behaving as a base:

Al2O3 + 6HCl → 2AlCl3 + 3H2O

  • Example of aluminium oxide behaving as an acid:

Al2O3 + 2NaOH → 2NaAlO2 + H2O

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Caroline

Author: Caroline

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Caroline graduated from the University of Nottingham with a degree in Chemistry and Molecular Physics. She spent several years working as an Industrial Chemist in the automotive industry before retraining to teach. Caroline has over 12 years of experience teaching GCSE and A-level chemistry and physics. She is passionate about creating high-quality resources to help students achieve their full potential.