Testing Aqueous Cations 2
Chemistry: Cambridge International GCSE Supplement, topic 12.5.2
Metal Hydroxides
Here are some more examples of the formation of precipitates:
Copper(II) hydroxide
- Copper ions (Cu2+) form the blue precipitate copper(II) hydroxide.
- Cu2+(aq) + 2OH-(aq) → Cu(OH)2(s).
Iron(II) hydroxide
- Iron(II) ions (Fe2+) form the green precipitate iron(II) hydroxide.
- Fe2+(aq) + 2OH-(aq) → Fe(OH)2(s).
Iron(III) hydroxide
- Iron(III) ions (Fe3+) form the brown precipitate iron(III) hydroxide.
- Fe3+(aq) + 3OH-(aq) → Fe(OH)3(s).
Ammonium ion
- Ammonium (NH4+) ions form water and ammonia. Ammonia gas evolves out of the solutions.
- NH4+(aq) + OH-(aq) → NH3(g) + H2O(l).
Chromium(iii) hydroxide
- Chromium(III) ions (Cr3+) form a green precipitate.
- The green precipitate dissolves in excess NaOH.
Test yourself on Testing Aqueous Cations 2
Which of the following metal ions forms a brown precipitate?
What colours are the following precipitates?