Using the iodine clock method to find the order of a reaction.

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Using the iodine clock method to find the order of a reaction.

Requirements:

  • 0-110  thermometer
  • boiling tubes (5)                                  
  • test-tubes
  • burettes (or graduated pipettes 1cm , 2cm  and 5cm )
  • potassium iodide solution, 1.00 mol dm  (15cm )
  • potassium peroxodisulphate(VI) (K S O ) solution, 0.0400 mol dm  (10cm )
  • sodium thiosulphate (Na S O ) solution, 0.0100 mol dm  (10cm )
  • freshly made starch solution (5cm )
  • stopwatch

Introduction:

        This reaction takes place when peroxodisulphate(VI) ions and iodide ions react together in solution to form sulphate(VI) ions and iodine. Here is a clear view of the balanced equation representing this reaction;

S O  (aq) + 2I  (aq) – 2SO  (aq) + I (aq)

Measuring the reaction can be done by following the colour of the iodine produced. This is the reason for the starch solution, as iodine forms an intense blue-black presence once they come together.

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        You can make the time taken to produce a particular amount of iodine obvious if you add thiosulphate ions to the mixture at the beginning, as thiosulphate ions turn iodine back to iodide ions. So no starch-iodine colour will appear until all of the thiosulphate has been used up, you will suddenly see the clear mixture transform into a blue-black. By measuring the length in time it takes for this to happen you will be able to find out how long it took to produce the equivalent amount of iodine.

        In this experiment I will be using this clock method ...

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