Summary of Qualitative Tests

The tables below provide cursory information about of many of tests chemists commonly perform to identify the presence of various substances.

I. Identification of Some Common Gases

Gas Test Result
Ammonia NH3
  1. Smell cautiously.
  1. Sharp odor.
  1. Test with litmus.
  1. Red litmus turns blue.
  1. Expose to HCl fumes.
  1. White fumes form, NH4Cl.
Carbon dioxide CO2
  1. Pass through limewater, Ca(OH)2.
  1. White precipitate forms, CaCO3.
Carbon monoxide CO
  1. Burn it and pass product through limewater, Ca(OH)2.
  1. White precipitate forms, CaCO3.
Hydrogen H2
  1. Allow it to mix with some air, then ignite.
  1. Gas explodes.
  1. Burn it—trap product.
  1. Burns with blue flame—product H2O turns cobalt chloride paper from blue to pink.
Hydrogen chloride HCl
  1. Smell cautiously.
  1. Choking odor.
  1. Exhale over the gas.
  1. Vapor fumes form.
  1. Dissolve in water and test with litmus.
  1. Blue litmus turns red.
  1. Add AgNO3 to the solution.
  1. White precipitate forms.
Hydrogen sulfide H2S
  1. Smell cautiously.
  1. Rotten egg odor.
  1. Test with moist lead acetate paper.
  1. Turns brown-black (PbS).
Oxygen O2
  1. Insert glowing splint.
  1. Bursts into flame.
  1. Add nitric oxide gas.
  1. Turns reddish brown.

II. Identification of Some Negative Ions

Ion Test Result
Acetate C2H3O2− Add concentrated H2SO4 and warm gently. Odor of vinegar released.
Carbonate CO3− Add HCl acid; pass released gas through limewater. White, cloudy precipitate forms.
Chloride Cl−
  1. Add silver nitrate solution.
  1. White precipitate forms.
  1. Then add nitric acid, later followed by ammonium hydroxide.
  1. Precipitate insoluble in HNO3 but dissolves in NH4OH.
Hydroxide OH− Test with red litmus paper. Turns blue.
Sulfate SO4− Add solution of BaCl2, then HCl. White precipitate forms; insoluble in HCl.
Sulfide S2− Add HCl and test gas released with lead acetate paper. Gas, with rotten egg odor, turns paper brown-black.

III. Identification of Some Positive Ions

Ion Test Result
Ammonium NH4+ Add strong base (NaOH); heat gently. Odor of ammonia.
Iron (II) Fe2+ Add solution of potassium ferricyanide, K3Fe(CN)6. Dark blue precipitate forms (Turnball’s blue).
Iron (III) Fe3+ Add solution of potassium ferrocyanide, K4Fe(CN)6. Dark blue precipitate forms (Prussian blue).
Hydrogen H+ Test with blue litmus paper. Turns red.

IV. Qualitative Tests of Some Metals

flame tests. Carefully clean a platinum wire by dipping it into dilute HNO3 and heating in the Bunsen flame. Repeat until the flame is colorless. Dip heated wire into the substance being tested (either solid or solution), and then hold it in the hot outer part of the Bunsen flame.

Compound of Color of Flame
Sodium (Na) Yellow
Potassium (K) Violet (use cobalt-blue glass to screen out Na impurities)
Lithium (Li) Crimson
Calcium (Ca) Orange-red
Barium (Ba) Green
Strontium (Sr) Bright red

hydrogen sulfide tests. Bubble hydrogen sulfide gas through the solution of a salt of the metal being tested. Check color of the precipitate formed.

Compound of Color of Sulfide Precipitate
Lead (Pb)                Brown-black (PbS)
    Copper (Cu) Black (CuS)
Silver (Ag)  Black (Ag2S)
     Mercury (Hg) Black (HgS)
Nickel (Ni) Black (NiS)
Iron (Fe)     Black (FeS)
        Cadmium (Cd)    Yellow (CdS)
  Arsenic (As)                 Light yellow (As2S3)
      Antimony (Sb)      Orange (Sb2S3)
Zinc (Zn)       White (ZnS)
Bismuth (Bi)     Brown (Bi2S3)