CIE IGCSE Chemistry

Revision Notes

8.1.2 Types of Oxides

Classifying Oxides

Acid and basic oxides

  • Acidic and basic oxides have different properties and values of pH
  • The difference in their pH stems from whether they are bonded to a metal or a nonmetal element
  • The metallic character of the element influences the acidic or alkaline behaviour of the molecule


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


Acidic oxides

  • Acidic oxides are formed when a nonmetal 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 SO2 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 NaOH, KOH and Ca(OH)2
Extended Only

Neutral & Amphoteric Oxides

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 a salt and water is formed
  • Two most common amphoteric oxides are zinc oxide and aluminum oxide
  • The hydroxides of both of these elements also behave amphoterically
  • Example of aluminium oxide behaving as a base:
Al2O3 + 6HCl → 2AlCl3 + 3H2O
  • Example for an aluminium oxide behaving as an acid:
Al2O3 + 2NaOH → 2NaAlO2 + H2O

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