Rates of reaction - kinetics (A2)
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I am carrying out the iodine clock reaction at school, using hydrogen peroxide, potassium iodide, sulphuric acid, sodium thiosulphate and starch. The results that I have got show that the order of reaction of the hydrogen peroxide, potassium iodide, sulphuric acid are all 1st order. However, with the thiosulphate, the graph which I drew for the rate against concentration, shows that there is a negative gradient. Therefore I am not sure what order this is as zero order is a straight horizontal line. Could you help me with this?
The thiosulphate is not a reactant in the reaction between peroxide and iodide. It is added as part of the experimental design to allow you to measure initial rates of the peroxide/iodide reaction by recording the time taken for the colour to change. The blue colour appears when the iodine produced by the reaction has used up the fixed amount of thiosulphate added.
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updated: 18 December 2006
