Question detail
Chemical changes case 128 salt-method. A student plans a salt preparation method. Which option is most creditworthy? Focus on products aqueous electrolysis suitable chemical tests where appropriate in Electrolysis of aqueous solutions, not on a neighbouring Unit 4.4 reaction idea.
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
MCQ
Type
practice
Style
Topic
Electrolysis
Question
- A. Chemical changes case 128 salt-method: Uses the correct reactants, separation step and crystallisation idea for products aqueous electrolysis suitable chemical tests where appropriate
- B. Chemical changes case 128 salt-method: Evaporates to dryness when crystals should be formed carefully (Electrolysis of aqueous solutions)
- C. Chemical changes case 128 salt-method: Adds indicator to every salt preparation regardless of method (products aqueous electrolysis suitable chemical tests where appropriate)
- D. Chemical changes case 128 salt-method: Names a salt but omits how excess solid or solution is handled (Electrolysis)
Answer
The correct option is Chemical changes case 128 salt-method: Uses the correct reactants, separation step and crystallisation idea for products aqueous electrolysis suitable chemical tests where appropriate.
Explanation
The correct option is Chemical changes case 128 salt-method: Uses the correct reactants, separation step and crystallisation idea for products aqueous electrolysis suitable chemical tests where appropriate. It is correct because it directly supports the approved learning objective to identify products of aqueous electrolysis using suitable chemical tests where appropriate in Electrolysis of aqueous solutions. The other options are incorrect because they blur a Unit 4.4 concept boundary: acid versus alkali versus base, oxidation versus reduction, displacement versus reduction, electrolysis versus electroplating, anode versus cathode, positive versus negative ions, oxidation state versus ionic charge, or strong acid versus concentrated acid.
Common mistake
Misidentifying the anode product
Students often think that oxygen is always produced at the anode in aqueous electrolysis, even when halide ions are present.
Explain that if halide ions (Cl⁻, Br⁻, I⁻) are present, the anode reaction will produce the corresponding halogen (Cl₂, Br₂, I₂) because the halide oxidation potential is lower than that of water. Use the reactivity series and ion potentials to predict the correct anode product, and remind students to test the gas with appropriate chemical tests (e.g., sodium hydroxide for chlorine, silver nitrate for bromine).
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