Rates of reaction - kinetics (A2)
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I have planned an investigation to determine the activation energy for a reaction between bromide/bromate solution, phenol and sulphuric acid. I will be varying temperature and using methyl red as a bleach.
I have determined that the order of reaction wrt bromide/bromate is first order, and second with respect to sulphuric acid. However, I can't understand what order phenol should be, because my results don't seem to give any trend when I vary the concentration of phenol. So I can't figure out what's happening. Also I am having difficulty finding an alternative method for this experiment.
Ulex replies
I am not at all sure what reaction you are expecting. The bromide/bromate/
acid mixture produces bromine, which then substitutes into the phenol giving 2,4,6-tribromophenol. This is what I would expect – is this what you were expecting?
What do you mean by saying that methyl red is a bleach? It would be bleached by the bromine but how does this help? Have you been timing the point where all the phenol has been ‘used up’ by reaction with bromine, so that the next bromine to be produced bleaches the methyl red?
Are you then treating this as one reaction when it is clearly two reactions in series? If so, I’m not altogether surprised that you are getting some strange results.
Taking your account at its face value, is it possible that the order with respect phenol for the sequence of reactions is zero?
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updated: 25 January 2008
