Chemistry WCH16/01 January 2021 | Edexcel International A Level Past Papers With Mark Scheme

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1. qualitative ion testing—Ba²⁺ identification via white precipitate, Cu²⁺ complex formation and color transitions, CO₂ confirmation by limewater, SO₄²⁻ detection via Ba²⁺ precipitation
2. transition metal chemistry—pale blue Cu(OH)₂ precipitation with NH₃, deep blue [Cu(NH₃)₄(H₂O)₂]²⁺ formation, ligand displacement with EDTA, color change tracking
3. redox titration—ClO₃⁻ reduction using SO₂ and Fe²⁺, subsequent AgCl precipitation, calculation of KClO₃ concentration, MnO₄⁻ titration, iron oxidation state tracking
4. practical error analysis—excess SO₂ effects, unremoved chloride impact on titration accuracy, overestimated concentration risks, procedural hazards with gas handling
5. azo dye synthesis—multi-step organic conversion: benzene to nitrobenzene, phenylamine, diazonium salt, coupling with naphthol, temperature-sensitive steps, reflux setup
6. purification techniques—minimum hot solvent usage, preheated funnel for filtration, Buchner filtration, desiccator drying for heat-sensitive dyes, melting point purity confirmation

Edexcel International AS/A Level Chemistry (WCH) Jan 2021

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Classification: Unit 6

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Chemistry WCH16/01 January 2021 | Edexcel International A Level Past Papers With Mark Scheme

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