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Iodine clock reaction

Description

A solution of hydrogen peroxide is mixed with one containing potassium iodide, starch and sodium thiosulfate. After a few seconds the colourless mixture suddenly turns dark blue. This is one of a number of reactions loosely called the iodine clock. It can be used as an introduction to experiments on rates / kinetics.

Credits

:
This is an experiment from the Practical Chemistry project, developed by the Nuffield Foundation and the Royal Society of Chemistry.
iodine-clock-reaction



Apparatus Chemicals

Eye protection

Balance (1 or 2 d.p.)

Beaker (1 dm3)

Beaker (250 cm3)

Volumetric flasks (1 dm3), 2

Measuring cylinder (50 cm3)

Measuring cylinders (100 cm3), 2

Stirring rod or magnetic stirrer and follower (optional)

Stopwatch/timer

Deionised/distilled water, 2 dm3.

Solution A (Note 1):

Soluble starch, 0.2g

Anhydrous sodium ethanoate (sodium acetate), 4.1 g

Potassium iodide, 50g

Sodium thiosulfate-5-water, 9.4g

Solution B (Note 1):

Glacial (concentrated) ethanoic acid (CORROSIVE), 30 cm3 (Note 2)

Hydrogen peroxide solution, 20 'vol' (IRRITANT), 500 cm3  (Note 2)

Refer to Health & Safety and Technical notes section below for additional information.

 








A solution of hydrogen peroxide is mixed with one containing potassium iodide, starch and sodium thiosulfate. After a few seconds the colourless mixture suddenly turns dark blue. This is one of a number of reactions loosely called the iodine clock. It can be used as an introduction to experiments on rates / kinetics.

ADDITIONAL INFORMATION

This is a resource from the Practical Chemistry project, developed by the Nuffield Foundation and the Royal Society of Chemistry. This collection of over 200 practical activities demonstrates a wide range of chemical concepts and processes. Each activity contains comprehensive information for teachers and technicians, including full technical notes and step-by-step procedures. Practical Chemistry activities accompany Practical Physics and Practical Biology.

The experiment is also part of the Royal Society of Chemistry's Continuing Professional Development course: Chemistry for non-specialists