Prepare a mixture of 18.5g KI, 0.5g of Na2S2O3 & 4ml of 0.1M CH3COOH in 1L of distilled water. Add enough universal indicator to produce a strong red colour. Add 1 ml of 40 vol. H2O2 to 200 ml of the solution and the colour changes from red to orange to yellow to green to blue to purple. The rate of colour change depends on the amount of H202. This can be illustrated by adding 1 ml to one sample of the solution and 2 ml to another.
The hardest part of this is working out the H2O2 and then adjusting the solution accordingly. I have seen a cheaper prac but I cant find it.
This prac is from Chemistry Activities, Book One, Nash and Hargreaves.(1990) and if you do it properly it is awesome.
