Rates of reaction - kinetics (A2)
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I am investigating the reaction between peroxodisulphate and iodide ions. I aim to find the order of reaction and possibly the activation energy by using a variety of techniques. I have already decided to use the iodine-clock and colorimeter to determine the rate of reaction but was wondering if it would be possible to determine the rate of reaction by using a titration. If so, would I need to quench the reaction and, if so with what? Is there another method that I could use?
Igloo writes
The iodine-clock method, using sodium thiosulphate and starch solutions, is the usual way of handling this investigation.
The use of a colorimeter (to detect the colour of iodine molecules as their concentration steadily increases) represents another valid approach.
A titration is probably inappropriate here. The reaction is being carried out in neutral conditions, so it isn’t feasible to add excess acid or alkali to “stop” the reaction whilst you carry out a titration at leisure. The traditional way of “freezing” the reaction is to plunge an extracted portion of the mixture into an ice bath, but I do not think that this will help here because the reaction is relatively fast, even at ice bath temperatures. In any case this is often an unsatisfactory procedure, because you never stop the reaction fully.
Another method you might wish to consider is linked to changes in conductivity. Given that the reactants are both ions, but that the products are mixtures of ions and molecules, there is bound to be a change in conductivity. Your school or college probably has some sort of conductivity meter which could be used in this investigation. Whether the change of conductivity in this process is measurable remains to be seen, that is investigated! Over to you!
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updated: 26 February 2004
