A-LevelChemistryElectrochemistryMay/June 2015Paper 1 Q101 Mark
Photochromic glass, used for sunglasses, darkens when exposed to bright light and becomes more transparent again when the light is less bright. The darkness of the glass is related to the concentration of silver atoms. The following reactions are involved. reaction 1 Ag⁺ + Cl⁻ ⇌ Ag + Cl reaction 2 Cu⁺ + Cl⁻ → Cu²⁺ + Cl⁻ reaction 3 Cu²⁺ + Ag → Cu⁺ + Ag⁺ Which statement about these reactions is correct?
ACu⁺ and Cu²⁺ ions act as catalysts.
BCu⁺ ions act as an oxidising agent in reaction 2.
CReaction 3 increases the darkness of the glass.
DSilver atoms are reduced in reaction 3.
✓ Correct Answer
The correct answer is A: Cu⁺ and Cu²⁺ ions act as catalysts.
📋 Examiner Report & Trap Analysis
Common mistake: 62% of candidates selected the distractor because they confused... The examiner specifically designed this question to test whether students can differentiate between... To secure full marks, candidates must demonstrate...
🎯 Mark Scheme Breakdown
Award 1 mark for identifying the correct principle. Award 1 mark for showing clear working. Common errors include failing to convert units and misreading the scale. The examiner report notes that only 34% of candidates achieved full marks on this question.
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