Question detail
What is the observation when sodium hydroxide is added to an aqueous solution of copper(II) ions? Explain the significance of this observation.
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At a glance
Question
Type
exam_style
Style
Topic
Reactions of ions in aqueous solution (A-level only)
Question
What is the observation when sodium hydroxide is added to an aqueous solution of copper(II) ions? Explain the significance of this observation.
Answer
When sodium hydroxide is added to an aqueous solution of copper(II) ions, a blue precipitate of copper(II) hydroxide forms. This indicates the presence of copper(II) ions in the solution. This answer is anchored to Aqueous ion tests (A-level only).
Explanation
When sodium hydroxide is added to an aqueous solution of copper(II) ions, a blue precipitate of copper(II) hydroxide forms. This indicates the presence of copper(II) ions in the solution. is the best answer because it directly supports the AQA A-Level Chemistry objective to required practical: carry out test-tube reactions to identify cations and anions. This reasoning is anchored to Aqueous ion tests (A-level only) in Reactions of ions in aqueous solution (A-level only), and it separates required from similar A-Level ideas rather than relying on a vague recall statement. Other options are weaker if they use the wrong evidence, calculation, mechanism, observation, unit, or conclusion for this subtopic.
Common mistake
Identifying Cations with Sodium Hydroxide
Students often incorrectly assume that all metal ions will produce a precipitate when reacted with sodium hydroxide.
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.
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