A-LevelChemistryElectrochemistry9701/12 · May/June 2015 · 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
A: Cu⁺ and Cu²⁺ ions act as catalysts.
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