Apparatus

Magnetic stirrer and follower (optional).
1dm beaker.


Chemicals

The quantities given are for one demonstration
75 cm of concentrated sulphuric acid (HSO).
9 g of malonic acid (propanedioc acid, CH(COH)).
8g of potassium bromate(V) (KBrO).
1.8g of manganese(II) sulphate (MnSO.HO).
750 cm of deionised water.


Before the Demonstration

Place 750 cm deionised water in a 1 dm beaker. Slowly, and with stirring, add 75 cm concentrated sulphuric acid carefully. The mixture will heat up to about 50. Allow it to cool back to room temperature. This will take some time. Weigh out the malonic acid, potassium bromate and manganese sulphate in weighing boats.

The Demonstration

Place the beaker of sulphuric acid on a magnetic stirrer and stir the solution fast enough for a vortex to form. A stirring rod can be used, but it is tedious and tends to detract from the demonstration. Add the malonic acid and potassium bromate.

When these have dissolved, add the manganese sulphate and observe what happens. A red colour should develop immediately. This will disappear after about one minute and thereafter the colour will oscillate from red to colourless with a time period of about 20 seconds for a complete oscillation.

This will continue with a gradually increasing time period for over ten minutes - long enough for most audiences to lose interest!