A student set up an experiment to investigate diffusion. A block of agar, 1.0 cm × 1.0 cm × 1.0 cm, was stained uniformly with a water-soluble blue dye. The block of agar was put into a test-tube containing 10 cm³ of distilled water at 20 °C. The intensity of the blue colour of the water after five minutes was measured. Four other experiments, A, B, C and D, were then carried out using different numbers of agar blocks, different sizes of agar blocks and different temperatures. All other variables were standardised. Which experiment would give a lighter blue colour in the water after five minutes compared to the first experiment? [Table showing size of each agar block/cm, number of agar blocks, temperature of distilled water/°C]
✓ Correct Answer
The correct answer is B: size of each agar block/cm: 0.5 x 0.5 × 0.5, number of agar blocks: 2, temperature of distilled water/°C: 20
📋 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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