Required practical: carry out test-tube reactions to identify cations and anions.

In the subtopic Aqueous ion tests (A-level only), this AQA A-Level Chemistry 7405 learning objective focuses on required practical: carry out test-tube reactions to identify cations and anions. It belongs to Reactions of ions in aqueous solution (A-level only), so revision should stay anchored to this exact subtopic rather than drifting into a generic GCSE-level chemistry summary. Approved keywords to use include required, practical, carry, test-tube, reactions. Ammonia. means a weak base that can react with metal ions in solution to form complex ions or precipitates Avoid the mistake of students often incorrectly assume that all metal ions will produce a precipitate when reacted with sodium hydroxide; instead, to correctly identify cations, remember that only certain metal ions form insoluble hydroxides. For example, when testing with sodium hydroxide, use the formula for the reaction: Metal Ion + NaOH → Metal Hydroxide (precipitate). For instance, Fe²⁺ + 2NaOH → Fe(OH)₂ (s) shows a green precipitate, while Na⁺ does not produce any precipitate. Always check the solubility rules for hydroxides For exam answers, when testing for metal ions with sodium hydroxide, observe the colour of the precipitate that forms. A clear, colourless solution that turns cloudy or forms a white precipitate indicates a hydroxide of a metal ion such as Ca²⁺ or Mg²⁺. A coloured precipitate (e.g., orange for Fe³⁺) immediately points to a specific ion. This visual cue saves time and reduces the need for further confirmatory tests