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However they produce one further hydrolysis reaction, as they are 3+ ions and not 2+ ions. When iron (III) metal-aqua ions are added to dilute solutions of sodium hydroxide or dilute ammonia, similar reactions to the 2+ ions occur. If left standing, the precipitate darkens and turns brown as Fe²⁺ ions become oxidised to Fe³⁺ by water and oxygen.Īddition of Limited OH- Ions to Fe³⁺ and Al³⁺ Metal-Aqua Ions The solution is initially pale green and upon adding ammonia or an alkali, a green iron (II) hydroxide precipitate forms.

The same type of reaction takes place with green iron(II)aqua ions. The reason a precipitate forms, is because the complex produced has no charge, i.e. OH- ions add to the complex formed to make a blue precipitate. When copper(II) ions are added to OH- ions, from dilute NaOH or dilute ammonia solution, the OH- ions remove a proton effectively from one of the water ligands. Precipitation Reactions of Metal Ions in SolutionĪddition of Limited OH- Ions to Cu²⁺and Fe²⁺Metal-Aqua Ions Precipitation Reactions of Metal Ions in Solution (A-Level Chemistry) Reactions of M²⁺(aq) and M³⁺(aq) Metal-aqua Ions with alkalisĪddition of OH- ions to metal-aqua ions, by dilute sodium hydroxide (NaOH) or dilute ammonia (NH4), results in the formation of insoluble precipitates.