Edexcel Chemistry: Inorganic Gas and Flame Tests

• Chemical tests notes for Edexcel IGCSE Chemistry, Topic 2: Inorganic chemistry

Tests for Gases

• Hydrogen is tested for using a burning splint at the open end of a test tube
• Hydrogen gas creates a 'squeaky pop' sound
• Oxygen is tested for using a glowing splint inserted into a test tube of the gas
• Oxygen gas exposure will cause the splint to relight
• Carbon dioxide is tested for by bubbling the gas through limewater (calcium hydroxide)
• Carbon dioxide exposure will cause limewater to turn milky or cloudy
• Ammonia is tested for using damp red litmus paper
• Ammonia gas will turn damp red litmus paper blue
• Ammonia forms a white smoke of ammonium chloride when hydrogen chloride gas, from concentrated hydrochloric acid, is held near it.
• Chlorine is tested for using damp litmus paper
• Chlorine gas will bleach damp litmus paper, turning it white

Flame Test

• A flame test is performed by taking a sample of the metal on a wire and putting it in a flame.
• Metals will turn flame a specific color, showing what metal it is

Flame Test Colors for Cations

• Lithium (Li+) turns flame red
• Sodium (Na+) turns flame yellow
• Potassium (K+) turns flame lilac
• Calcium (Ca2+) turns flame orange-red
• Copper (Cu2+) turns flame blue-green

Identifying Cations Using NaOH(aq)

• Test for NH4+ using NaOH(aq) and identify the gas evolved
• Test for Cu2+, Fe2+, and Fe3+ using NaOH(aq)
• Ammonia reacts with NaOH(aq) forming NH3(g)
• Use damp red litmus paper for ammonia, which will turn blue if ammonia gas is present
• Copper(II) produces a blue precipitate
• Iron(II) produces a green precipitate
• Iron(III) produces a brown precipitate

Identifying Anions

• Tests for Cl-, Br- and I- using acidified silver nitrate solution, SO₄²⁻ using acidified barium chloride solution, CO₃²⁻ using hydrochloric acid and identifying the gas evolved
• Halide ions are tested for by adding dilute nitric acid, followed by silver nitrate solution
  • Chloride gives a white precipitate
  • Bromide gives a cream precipitate
  • Iodide gives a yellow precipitate
• Sulfate ions are tested for by adding dilute hydrochloric acid, followed by barium chloride solution
  • A white precipitate will form when sulfate ions are in this solution
• Carbonate ions are tested for with dilute acids to create carbon dioxide
  • Pass the gas through limewater; if the limewater goes cloudy, the gas is CO₂

Test for Water

• Anhydrous copper(II) sulfate is white
  • When water is present, it turns blue

Testing Water Purity

• Water purity can be tested by evaporating it on an evaporating dish or by measuring its boiling point