A-LevelBiologyBiological moleculesOct/Nov 2019Paper 1 Q81 Mark
A student was asked to estimate the concentration of reducing sugar in an unknown solution using the Benedict's test. Five reducing sugar solutions with different concentrations were provided in order to produce a calibration curve. The student added 2 cm³ of Benedict's solution to each of the reducing sugar solutions, heated them in a water-bath and recorded the time taken for the first appearance of a colour change. Which variables should the student standardise, when carrying out the Benedict's test on each reducing sugar solution, to ensure the results are comparable? 1 volume of reducing sugar used 2 the temperature of the water-bath 3 the time the solutions are heated
A1, 2 and 3
B1 and 2 only
C1 and 3 only
D3 only
✓ Correct Answer
The correct answer is B: 1 and 2 only
📋 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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