Belousov-Zhabotinsky reaction

The Belousov-Zhabotinsky reaction is a so called oscillating diffusing reaction. Summarized there are three processes: A, B and C. In process A bromate turns into bromide, in process B bromide turns back into bromate and in process C the products from the reaction will react with each other. The critical concentration of bromide causes the oscillating pattern as it fluctuates from process A to process B. This reaction is made visible by using the ferroin indicator, which turns red when it is in its reduced form in process A and turns blue when it is oxidised in process B as shown in the left picture.

Processes

BZ-mechanism1

We use 5 solutions to create the reaction:

Solution A: 2 ml sulphuric acid and 5g sodium bromate (NaBr03) in 67 ml water                   Solution B: 1g sodium bromide (NaBr) in 10 ml water                                                             Solution C: 1g malonic acid in 10 ml water                                                                             Solution D: 1 ml ferroin (25 mM phenanthroline ferrous sulphate)                                         Solution E: 1g Triton X-100 (a kind of detergent) in 1 litre of water

IMG_7874

We put 6 ml of solution A into a petri dish, add 1-2 ml of solution B and 1 ml of solution C. The solution turns a brownish colour. After a minute or so the brown colour will disappear. Once this has happened, we add 1 ml of solution D and a drop of solution E and the liquid tIMG_7880urns red. We swirl the petri dish gently to mix the solutions. It will turn blue and then quickly reverts to red again. Gradually, blue spots will appear randomly and the reaction will start. Below there is a video of our first experiment. In real time the reaction lasts about 45 minutes as it evolves chaotically, in the video it has been speed up 8 times.

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