GCSE Chemistry (AQA)

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Identifying Compounds Using Chemical Tests

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Chemical analysis Identification of ions by chemical and spectroscopic means

Identifying Compounds Using Chemical Tests

5:35 Tests for Ions
Spec 4.8.3.1
Previous Tests for Gases Next Flame Tests
  • Unknown ionic compounds can be identified through multiple chemical tests.
  • Flame tests and adding certain chemicals help determine the ions present in a compound.
  • These tests are not applicable for covalent compounds as they lack ions.
  • Each test checks for a specific ion, and results must be considered together to identify the compound.
  • Both positive (cations) and negative (anions) ions in an ionic compound need identification.
  • Example: An ionic compound with calcium ions (Ca�����) and carbonate ions (CO��������).
  • Flame tests involve holding a sample-coated wire in a Bunsen flame to observe color changes indicating metal ions.
  • A green flame suggests the presence of Cu����� ions.
  • Sodium hydroxide can be added to form a precipitate, confirming the cation by color.
  • A blue precipitate confirms Cu����� ions.
  • Hydrochloric acid and barium chloride can test for sulfate ions, forming a white precipitate if present.
  • No reaction indicates no sulfate ions.
  • Nitric acid and silver nitrate test for halide ions, forming a colored precipitate.
  • A yellow precipitate confirms I��� ions.
  • Exam questions may require identifying ions and determining the full chemical formula of an ionic compound.
  • The unknown compound contains Cu����� and I��� ions.
  • The chemical formula is determined using the swap and drop method, resulting in CuI���.

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