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Homework Help: Belousov-Zhabotinsky oscillating reaction

  1. May 6, 2006 #1
    Here's a physics student trying to perform the Belousov experiment, that is the chemical clock that changes its color from red to blue and viceversa.

    I've been able to "borrow" the following reactants:

    H2S04(sulfuric acid) 1,5M
    NaBr03(sodium bromate) 0.08M
    CH2(COOH)2(malonic acid) 0.002M
    Ce(SO4)2 0.1M
    ferroin 0.0003.M

    I've tried mixing them but I've seen no oscillations. The original recipe says that Ce2(SO4)3 should be used (Ce3+//Ce4+ is what oscillates). What do you suggest I should do? In what order do I mix the reactants? Is this a bad recipe?
    Thanks for your help!
  2. jcsd
  3. May 7, 2006 #2


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    1. I think your malonic acid is too dilute. I recommend 0.2 to 0.3M acid.

    2. The order of mixing should not matter.

    3. I think your Ce(SO4)2 is too concentrated. I would use something like 0.002M Ce(4+) solution. Or did you just switch the concentrations of the acid and ceric sulfate when you typed it here ?

    4. If switching the concentrations doesn't help (or you just mistyped it here), you could try ceric ammonium nitrate instead of ceric sulfate.

    5. What color do you see when you prepare the solution ?

    6. The typical period of oscillations for the specified concentrations is of order a minute. So, you need to have the solution be stirred continuously for at least that long to see a color change. A better idea (once you have a working solution, at least) is to use a magnetic stirrer.
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