Chemistry- Test for positive ions

Chemistry C3- tests for positive ions

  • Flame tests
  • Coloured precipitate test
  • Ionic Reactions
HideShow resource information
  • Created by: Rachael
  • Created on: 07-05-10 21:05

Flame test

Dip a wire loop into some hydrochloric acid to clean it.

Put the loop into a powdered sample of the compound to be tested, then place the end in a blue Bunsen fame.

Once heated the compounds of some metals give a characteristic colour flame.

1 of 4

Sodium, Na+, gives a yellow/ orange flame

Calcium, Ca2+, gives a brick-red flame

Potassium, K+, gives a lilac flame

Copper, Cu2+, gives a blue-green flam

2 of 4

Add sodium hydroxide and look for a coloured preci

Many metal hydroxides are insoluble and precipitate out of solution when formed. Some of these hydroxides have a characteristic colour.

Add a few drops of sodium hydroxide solution to the solution of the compound you wish to identify.

If you get a coloured insoluble hydroxide, you can tell which metal was in the compound.

3 of 4

  • Calcium, Ca2+, forms a white precipitate and the ionic reaction is:
    • Ca2+(aq) + 2OH-(aq) -> Ca(OH)2 (s)
  • Copper(II), Cu2+, forms a blue precipitate and the ionic reaction is:
    • Cu2+(aq) + 2OH-(aq) -> Cu(OH)2 (s)
  • Iron(II), Fe2+, forms a sludgy green precipitate and the ionic reaction is:
    • Fe2+(aq) + 2OH-(aq) -> Fe(OH)2 (s)
  • Iron, Fe3+, forms a reddish brown precipitate and the ionic reaction is:
    • Fe3+(aq) + 3OH-(aq) -> Fe(OH)3 (s)
  • Aluminium, Al3+, forms a white precipitate at first but then redissolves in excess NaOH to form a colourless solution and the ionic reaction is:
    • Al3+(aq) + 3OH-(aq) -> Al(OH)3 (s)
    • Then: Al(OH)3 (s) + OH-->Al(OH)4 -(aq)
4 of 4




I thiink that this is fab!! It helped me loads :) Thanks!

Similar Chemistry resources:

See all Chemistry resources »See all Testing and analysing substances resources »