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Experiment to determine the factors which affect the rate of oxidation of acidified potassium iodide solution by hydrogen peroxide.

Plan

As described in my preliminary introduction I intend to carry out an investigation to determine the factors which affect the rate of oxidation of acidified potassium iodide solution by hydrogen peroxide.

H202 + 2KI + H2SO4 = K2SO4 + 2H2O + I2

I intend to vary the amount of potassium iodide entered into the 100cm³ solution (potassium iodide included in the solution). Potassium iodide is the independent variable. I plan to keep the volume of the solution at 100cm³. The dependant variable is time as this will vary depending on how quickly the solution turns a purple/black colour and the black cross marked on the paper below is not visible. I intended to keep the amount of sulphuric acid constantly at 40 cm³ also keeping the amount of hydrogen peroxide at 15 cm³ and the amount of special indicator at 5 cm³. In some cases where potassium iodide, sulphuric acid, hydrogen peroxide and the special indicator do not equal 100 cm³. Water is added to the solution to equal 100 cm³. . Potassium iodide is the independent variable therefore its volume must be changed in every solution.

The apparatus required for this experiment consists of a stop clock, a 100 cm³ beaker, a 100 cm³ measuring cylinder, a 50 cm³ measuring cylinder, a 10 cm³ measuring cylinder and a glass rod. The diagrams of apparatus can be found on page 4.

Method

  1. Collect your apparatus.
  2. Draw a black cross on a piece of paper using a marker pen.
  3. When carrying out the experiment place this underneath the 100 cm³ beaker.
  4. Pour 40 cm³ of potassium iodide and 40 cm³ of sulphuric acid into the 100 cm³ measuring cylinder.
  5. Pour 15 cm³ of hydrogen peroxide into the 50 cm³ measuring cylinder.
  6. Pour 5cm cm³ of special indicator containing starch into the 10 cm³ measuring cylinder.
  7. Pour all the liquids into the 100 cm³ beaker and start the stop clock.
  8. Stir the solution until it turns a blue/black colour and the cross below is not visible.
  9. Record the time it took for the solution to change colour.
  10. Wash your apparatus.  
  11. Pour 30 cm³ of potassium iodide and 40 cm³ of sulphuric acid into the 100 cm³ measuring cylinder and also 5 cm³ special of indicator.
  12. Pour 15 cm³ of hydrogen peroxide into the 50 cm³ measuring cylinder.
  13. Pour 10 cm³ of water into the 10 cm³ measuring cylinder.
  14. Pour all the liquids into the 100 cm³ beaker and start the stop clock.
  15. Stir the solution until it turns a blue/black colour, record the time when the black cross is not visible.
  16. Wash your apparatus.  
  17. Pour 25 cm³ of potassium iodide, 40 cm³ of sulphuric acid and 5 cm³ of special indicator into the 100 cm³ measuring cylinder.
  18. Pour 15 cm³ of hydrogen peroxide into the 50 cm³ measuring cylinder.
  19. Pour 10 cm³ of water into the 10 cm³ measuring cylinder.
  20. Pour all the liquids into the 100 cm³ beaker and start the stop clock.
  21. Stir the solution until it turns a blue/black colour and the black cross is not visible.
  22. Record the time.
  23. Pour 15 cm³ of potassium iodide, 40 cm³ of sulphuric acid and 5 cm³ of special indicator into the 100 cm³ measuring cylinder.
  24. Pour 15 cm³ of hydrogen peroxide and 25 cm³ of water into the 50 cm³ measuring cylinder.
  25. Pour all the liquids into the 100 cm³ measuring cylinder, start the stop clock and stir the mixture.
  26. Wash your apparatus.
  27. Stir the solution until it turns a blue/black colour and the cross underneath is not visible.
  28. Record the time taken.
  29. Wash your apparatus.
  30. Pour 10 cm³ of potassium iodide, 40 cm³ of sulphuric acid and 5 cm³ of special indicator into the 100 cm³ measuring cylinder.
  31. Pour 15 cm³ of hydrogen peroxide and 30 cm³ of water into the 50 cm³ measuring cylinder.
  32. Pour all the liquids into the 100 cm³ beaker and start the stop clock.
  33. Stir the mixture until the black cross is not visible.
  34. Record the time.
  35. Record all your results in a table and repeat the experiment.
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NOTE: Potassium iodide, sulphuric acid and special indicator containing starch can be mixed, i.e. in the same measuring cylinder. Hydrogen peroxide and water can also be mixed together.

Fair test

To ensure a fair test I used the same equipment for the duration of the experiment. I kept these volumes the same throughout the whole experiment, sulphuric acid 40 cm³, hydrogen peroxide 15 cm³ and the special indicator containing starch at 5 cm³. These values were kept the same to determine the factors which affect the rate of oxidation of acidified potassium iodide solution by hydrogen ...

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**** A well planned and conducted experiment with a detailed method. The analysis and explanation are slightly weaker with repetition of points and no attempt at quantitative analysis.