To test a compound, dip a nichrome (clean) wire
loop into a sample of the compound and put it in
the clear blue part of the Bunsen flame. Make
sure it is clean by dipping it into hydrochloric
acid and rinsing it with distilled water.
Some metal ions form a coloured precipitate with NaOH
Many metal hydroxides are insoluable and precipitate out of
solution when formed. Some have a characteristic colour
Add a few drops of sodium hydroxide solution to the solution of the mystery
compound. If you get a coloured compound you can tell which metal it was.
Calcium - white (Ca2+ + 2OH- = Ca(0H)2
Copper(II) - blue (Cu2+ + 2OH- = Cu(0H)2
Iron(II) - green (Fe2+ + 2OH- = Fe0H)2
Iron(III) - brown (Fe3+ + 3OH- = Fe(0H)3
Aluminium - White at first then redissolves in excess NaOH to form a colourless solution. (Al3+ +
3OH- = Al(0H)3 then Al(OH)3+ OH- = Al(OH)4