A-LevelChemistryAtoms, molecules and stoichiometryMay/June 2011Paper 1 Q101 Mark
Tanzanite is used as a gemstone for jewellery. It is a hydrated calcium aluminium silicate mineral with a chemical formula Ca2AlxSiyO12(OH).6½H2O. Tanzanite has Mr of 571.5. Its chemical composition is 14.04% calcium, 14.17% aluminium, 14.75% silicon, 54.59% oxygen and 2.45% hydrogen. (Ar values: H = 1.0, O = 16.0, Al = 27.0, Si = 28.1, Ca = 40.1) What are the values of x and y?
Ax: 1, y: 1
Bx: 2, y: 3
Cx: 3, y: 3
Dx: 6, y: 1
✓ Correct Answer
The correct answer is C: x: 3, y: 3
📋 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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