chemical tests

• what is the test for ammonium ions?

  add sodium hydroxide, test gas with damp red litmus paper. ammonia will turn it blue, indicating presence of ammonium ions
• what is the test for metal cations?

  burning them: Lithium = red; sodium = yellow; potassium = lilac; calcium= orange/red; copper = blue/green
• testing metals with sodium hydroxide:

  • add a few drops of NaOH- to the solution
  • metal hydroxides are insoluble, so a precipitate is formed
  • Cu2+ = blue precipitate
  • Fe2+ = green
  • Fe3+ = brown
• testing for gases:

  • chlorine bleaches damp blue litmus paper
  • oxygen relights a glowing splint
  • hydrogen extinguishes a lit splint with a squeaky pop
  • carbon dioxide turns limewater cloudy
  • ammonia turns damp red litmus paper blue
• what is the test for water?

  add white anhydrous copper sulphate, water will turn it blue. to test if the water is pure, find its boiling and freezing points
• testing for halide anions:

  • add dilute nitric acid (to remove carbonate or sulfite ions), followed by silver nitrate solution
  • Cl- gives white precipitate of silver chloride
  • Br- gives cream precipitate of silver bromide
  • I- gives yellow precipitate of silver iodide