cations test

• 1 - clean a platinum wire loop, dipping in some dilute HCL, holding over a bunson burner until it burns with no colour
• 2 - Dip loop into sample you want to test and put it back into flame. Record the colour of flame
• Colours detect different ions
• cation flame test only works for samples containing a single metal ion. A mixture of metal ions causes flame colours of some ions to be hidden
• compounds of some metals burn with a characteristic colour
• you can test for metal ions by heating the substance and seeing what colour it burns with
• lithium ions burn with a crimson flame
• sodium ions burn with a yellow flame
• potassium ions burn with a lilac flame
• calcium ions burn with an orange - red flame
• copper ions burn with a green flame
• only works with samples that contain a single metal ion, a mixture of metal ions causes the flame colours of some ions to be hidden
• some metals are insoluble and precipitate out of solution when formed, having a characteristic colour. In this test, add a couple drops of sodium hydroxide solution to a solution of mystery compound
• calcium will form a white precipitate
• copper (II) will form a blue precipitate
• iron (II) will form a green precipitate
• iron (III) will form a brown precipitate
• Aluminium will form white at first, then redissolves in excess NaOH to form a colourless solution
• magnesium will form a white precipitate when an insoluble hydroxide is formed
• the equation for the formation of aluminium ( Al 3+) precipitate is

  3+

  Al + 3OH -> Al(OH)

  3