Test for ions:

(i)               Halide ions (Cl^- , Br^- , I^- ):

To sample solution which we have taken in the test tube we add dilute nitric acid to it followed by the silver nitrate solution.

A white precipitate will be formed if there is presence of chloride ions in it.

NaCl + AgNO₃  → NaNO₃ + AgCl

                                 (white)

The precipitate is soluble in excess of ammonium solution.

Pale yellow / cream/ off white precipitate for bromide ions.

NaBr + AgNO₃ → NaNO₃ + AgBr

                               (pale yellow)

The precipitate is soluble partially in the ammonium solution.

We obtain Yellow precipitate if the iodide ions are present in it.

                                  NaI + AgNO₃ → NaNO₃ + AgI

                                                                  (yellow)

The precipitate formed is not soluble in the ammonium solution.

(ii)            For Sulphate (SO₄^2- ) ions:

To the sample solution taken in attest tube we add dilute nitric acid followed by barium chloride or barium nitrate solution. A white precipitate will be genearted if there is presence of sulphate ions.

CaSO₄ + BaCl₂ → CaCl₂ + BaSO₄

                                  (white)

(iii)          Sulphite (SO₃^-) ions:

A salt containing sulphite ions will give a choking smelling , acidic gas (that turns damp blue litmus red) (SO₂) when we heat sample solution with the dilute hydrochloric acid.

ZnSO₃ (aq) + HCl (aq) → ZnCl₂ (aq)+ SO₂ (g) + H₂O (aq)

(iv)          For Carbonate (CO₃^2-) ions:

To the sample solution taken in a test tube to which we add dilute hydrochloric or sulphuric acid. Effervescence of a gas is seen which turns lime water cloudy .

(v)             Ammonium (NH₄⁺) ions:

We add dilute sodium hydroxide solution to sample solution and heat the solution. A pungent smelling gas is formed (ammonia), if ammonium ions are present, they turns damp red litmus paper blue.

(vi)          Iron (II) (Fe²⁺) ions:

A solution containing iron(Fe²⁺) ions will give dirty green precipitate on addition of aqueous sodium hydroxide or ammonium solution. The solution turns brown at the surface because of oxidation to Fe(OH)₃ by air.

FeCl₂ (aq) + NaOH (aq) → Fe(OH)₂ (s) + NaCl(aq)

                                   (dirty green)

(vii)        Iron (III) (Fe³⁺) ions:

Solutions of compounds containing iron (III) ions will give red brown / dirty brown precipitate on addition of the aqueous sodium hydroxide or the ammonium solution.

FeCl₃ (aq) + NaOH (aq) → Fe(OH)­₃ (s) + NaCl (aq)

                                 (reddish brown)

(viii)     Nitrate (NO₃^-) ions:

To the sample solution taken in the test tube we add aqueous sodium hydroxide to it which is then followed by the aluminium powder and then heat the mixture. A pungent smelling gas is evolved which turns damp red litmus blue if there are present nitrate ions in it.

This happens as aluminium reduces nitrate ions to ammonium ions which reacts with hydroxide ions to liberate ammonia.

Brown ring test: can be performed by adding freshly prepared iron (II) sulphate to the solution and then add the concentrated sulphuric acid slowly sliding along the side of test tube. A broen ring appears if there are present nitrate ions in it.

(ix)          Aluminium (Al³⁼) ions:

To the sample solution taken in a test tube add sodium hydroxide or ammonium solution. A white gelatinous precipitate will be formed if there is presence of aluminium ions in it.

Lead and Zinc compounds behave in a similar manner. Unlike the hydroxides of aluminum and zinc hydroxide, lead, also dissolves in aqueous ammonia to form a colorless, water-soluble ammine complex.