CHEM - Chemical Tests
Chemistry, chemical tests, gases, metals, cations, anions, water - IGCSE | IBDP | DSE | GCE | AP Chemistry
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
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.
II. Test for sulfate (SO42-) 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.
SO42-(aq) + Ba2+(aq) → BaSO4(s)
III. Test for carbonate (CO32-) ions
Method: Add dilute acid, and bubble the gas formed into limewater.
Result: Carbonate ions react with dilute acid to form CO2 gas (CO32-(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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