One of these experiments is called the ‘Iodine Clock Reaction’ which was discovered by Hans Heinrich Landolt in 1886 and is a classical demonstration experiment that displays chemical kinetics in action. Two solutions are mixed, and at first there is no visible reaction, but after a short time delay, the liquid suddenly turns dark blue-black due to the formation of a triiodide-starch complex. Depending on the amount of one of the chemicals present (the thiosulphate), the sudden turning of the white liquid to blue-black can be controlled.

We set our experiment up with different concentrations of the thiosulphate solution roughly in the form of a clock-face and the idea was to see 1 change the quickest, and 12 the slowest. The experiment worked perfectly (bar a couple of early additions) and presented the boys with the opportunity to discuss the principles of chemical kinetics, which - as usual - they did with aplomb.

Well done, 8W!

If you'd like to see the reaction set to music with stunning effect, do watch the short clip at this link: Iodine Clock Reaction Timed to Tchaikovsky's Russian Dance from The Nutcracker.

Bryony Carpenter
Science Teacher