Colorimetry questions in 9701 Paper 5 ask you to make standards by dilution, choose the filter, zero the colorimeter, draw a calibration line and use it, for an unknown concentration or to follow a rate. Here you make standards of aqueous iodine, calibrate a colorimeter, read an unknown off the line and then follow the reaction of iodine with propanone. Watch the set-up built step by step, then build it yourself and check it against the points the examiners look for.
Examiner reports used: 9701 June 2024 and November 2024 (Paper 5 colorimetry questions), June 2023 and June 2025 (safety); the June 2026 mark scheme is cited where no report exists yet.
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Measure each volume of stock with a burette, make up to the mark with distilled water in a 100.0 cm³ volumetric flask, then stopper and invert.
A filter of the complementary colour, the light the solution absorbs most; zero with a blank of distilled water; a clean cuvette filled to the same level, held by the frosted sides.
Absorbance against concentration: a straight line through the origin, anomalies left out, absorbance directly proportional to concentration. Read unknowns across and down.
Volumes by volumetric pipette, stopwatch started on mixing, absorbance at regular times; the shape of absorbance against time gives the order.
More set-ups: all chemistry Paper 5 set-up builders. Then practise the written questions in the Paper 5 trainer. The experiment, readings and wording on this page are our own.