Awesome Oscillating Reaction (Briggs-Rauscher Reaction)

Introduction:

The Briggs-Rauscher reaction is an awesome reaction which looks like a magic. When three solutions are mixed, the colour of the solution will oscillating between colourless ,amber and dark blue.

Procedure:

1. Three solutions are prepared as below:

• Solution A:100ml water + 1.5g malonic acid + 0.4g manganese (II) sulfate + 0.1g starch
• Solution B: 90ml water + 10ml 1.0M sulfuric acid + 4.3g potassium iodate
• Solution C:100ml 10% hydrogen peroxide

2. Mix three solutions together , you will get better result if magnetic stirrer is used.

3. Awesome oscillating reaction will start!

4. The reaction will ended after about 5 -10 minutes and final solution is in dark blue colour.

Principal:

The chemical mechanism of this reaction is very complex and it mainly divides into two parts：

1.Non-radical process

-produce iodide ion[dark blue colour] from malonic acid, iodate and iodine

2.Radical process(occurs only when iodine quantities is low) :

-produce iodine[amber colour] and oxygen from hydrogen peroxide and iodate

In here, manganese (II) sulfate is a catalyst and starch is an indicator.

Notes:

1. If more solutionA is added, the oscillating cycle turn from dark blue to colourless more quickly and the reaction ends with colourless colour.

2. If more solutionB is added, th oscillating cycle turn from colourless to dark blue more quickly and reaction ends with dark blue colour.

3. If more solutionC is added , you won’t get dark blue in the initial few oscillating cycles.

4. Hydrogen peroxide and sulfuric acid are both corrosive, pay special attention when you deal with them.

5. Potassium iodate is difficult to be dissolved in water, so hot water is preferred to use.