Halides (AQA GCSE Chemistry)

• Negatively charged non-metal ions are known as anions
• You must be able to test for halide ions
  • These are the ions formed by the elements in Group 7 

How to test for halide ions

• Add silver nitrate solution, AgNO₃, in the presence of nitric acid 
• If a halide is present it forms a silver halide precipitate
• For example, the following reaction occurs between aqueous potassium chloride and silver nitrate solution:

potassium chloride +  silver nitrate   →  potassium nitrate + silver chloride 

KCl (aq)   +     AgNO₃ (aq)   →  KNO₃ (aq)  +  AgCl (s)   

• In this case, the silver halide formed is silver chloride, which forms a precipitate
  • This is represented using the state symbol, (s)
• The ionic equation for this reaction is:

Ag⁺ (aq) + Cl^– (aq) → AgCl (s)

• Depending on the halide present, a different coloured precipitate is formed, allowing for the identification of the halide ion
  • Silver chloride forms a white precipitate
  • Silver bromide forms a cream precipitate

  • Silver iodide forms a yellow precipitate

• The general equation for the formation of the precipitate is:

Ag⁺ (aq) + X^– (aq) → AgX (s)

Halide test

Each silver halide produces a precipitate of a different colour