Colourful catalysisHydrogen peroxide oxidises sodium thiosulphate to sulphuric acid.

Starting from an alkaline solution, the sulphuric acid produced by the reaction neutralises the sodium hydroxide and the resulting pH change can be followed using universal indicator which changes from blue to green to yellow to orange-red.

Adding an ammonium molybdate catalyst significantly speeds up the colour change.

Colourful catalysis

Colourful catalysis – risk assessment