This makes them a bit tougher to identify in an unknown solution.
Step OneThe easiest way to start is to add a few drops of NaOH:
Muddy Brown Precipitate = Ag+
No Precipiatate = Na+ or NH4+ (you will not be asked to tell these two ions apart in an assessment)
White Precipitate = any of the others
Step TwoIf a white precipitate has formed, add another 2-3 mL of NaOH:
Precipitate Remains = Ba2+ or Mg2+
Precipitate Disappears (redissolves) = Pb2+, Zn2+or Al3+
Barium or Magnesium?
Collect a new sample and add about 1 mL of sulfuric acid. The sulfate ions will form a white precipitate with barium ions, but not with magnesium:
White Precipitate = Ba2+
No Precipitate = Mg2+
Lead, Zinc or Aluminium?
Collect a new sample and add a few drops of potassium iodide (KI):
Yellow Precipitate = Pb2+
No Precipitate = Al3+or Zn2+
Add excess/concentrated ammonia. Both will form a white precipitate with the hydroxide ions in ammonia (it is a base), but zinc will redissolve, forming a complex ion with the ammonia molecules. Aluminium will not make this complex.
No Precipitate = Zn2+
White Precipitate = Al3+