Test for Gases

I. Test for Hydrogen

Method: Place lit splint at the open end of a test tube with the gas.

Result: Burns with a 'squeaky pop' noise.

2H₂(g) + O₂(g) → 2H₂O(l)

II. Test for Oxygen

Method: Place lit splint at the open end of a test tube with the gas.

Result: Splint relights.

III. Test for Carbon Dioxide

Method: Bubble gas through limewater (Ca(OH)₂).

Result: Limewater turns milky and cloudy.

CO₂(g) + Ca(OH)₂(aq) → CaCO₃(s) + H₂O(l)

IV. Test for Ammonia

Method: Put damp red litmus paper into test solution.

Result: Litmus paper turns blue because of OH^- ions.

NH₃(g) + H₂O(l) → NH₄⁺(aq) + OH^-(aq)

V. Test for Chlorine

Method: Put damp litmus paper into test solution.

Result: Litmus paper is bleached and turns white.

Flame Test for Metals

Method: Place a sample of metal on a platinum wire and put it in a non-luminous Bunsen flame.

Result: Each metal will show a specific color on a flame.

Test for Cations

I. Test for ammonium (NH₄⁺) ions

Method: Add aqueous sodium hydroxide (NaOH) to the test solution, and use damp red litmus paper.

Result: Ammonium ion reacts with hydroxide ion to form ammonia gas and water. (NH₄⁺(aq) + OH^-(aq) → NH₃(g) + H₂O(l)) The damp red litmus paper turns blue due to the presence of ammonia.

II. Test for Cu²⁺, Fe²⁺, Fe³⁺

Method: Add aqueous sodium hydroxide (NaOH).

Result: Precipitates of different colors form.

Test for Anions

I. Test for Halide Ions

Method: Add a few drops of dilute nitric acid (HNO₃) to react with any carbonate ions that may be present. Add silver nitrate (AgNO₃) solution.

Result: Precipitates of different colors form.

II. Test for sulfate (SO₄^2-) ions

Method: Add a few drops of dilute hydrochloric acid (HCl) to react with any carbonate ions that may be present, and then add barium chloride (BaCl₂) solution.

Result: White precipitate forms.

SO₄^2-(aq) + Ba²⁺(aq) → BaSO₄(s)

III. Test for carbonate (CO₃^2-) ions

Method: Add dilute acid, and bubble the gas formed into limewater.

Result: Carbonate ions react with dilute acid to form CO₂ gas (CO₃^2-(aq) + 2H⁺(aq) →  CO₂(g) + H₂O(l)). When carbon dioxide gas is bubbled into limewater, the limewater turns milky and cloudy.

Test for Water

Chemical Test for Water

Method: Add water to anhydrous copper(II) sulfate (CuSO₄). 

Result: The white powder turns blue.

CuSO₄(s) + 5H₂O(l) → CuSO₄·5H₂O(s)

Physical Test for Purity of Water

Method: Boil/freeze water and measure its boiling point/freezing point.

Result: If the water is pure, the boiling point is 100°C, and the freezing point is 0°C. If the water contains impurities, the boiling/freezing point is different.

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