Question detail
What is the observation when aqueous copper(II) ions react with sodium hydroxide?
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
MCQ
Type
practice
Style
Topic
Reactions of ions in aqueous solution (A-level only)
Question
- A. A blue precipitate forms
- B. A green precipitate forms
- C. No precipitate forms
- D. A white precipitate forms
Answer
A blue precipitate forms
Explanation
The correct option is A blue precipitate forms. A blue precipitate forms 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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