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

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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 100cmï¿½ solution (potassium iodide included in the solution). Potassium iodide is the independent variable. I plan to keep the volume of the solution at 100cmï¿½. 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.

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I intended to keep the amount of sulphuric acid constantly at 40 cmï¿½ also keeping the amount of hydrogen peroxide at 15 cmï¿½ and the amount of special indicator at 5 cmï¿½. In some cases where potassium iodide, sulphuric acid, hydrogen peroxide and the special indicator do not equal 100 cmï¿½.

Water is added to the solution to equal 100 cmï¿½. . 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 cmï¿½ beaker, a 100 cmï¿½ measuring cylinder, a 50 cmï¿½ measuring cylinder, a 10 cmï¿½ 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 cmï¿½ beaker.

4. Pour 40 cmï¿½ of potassium iodide and 40 cmï¿½ of sulphuric acid into the 100 cmï¿½ measuring cylinder.

5. Pour 15 cmï¿½ of hydrogen peroxide into the 50 cmï¿½ measuring cylinder.

6. Pour 5cm cmï¿½ of special indicator containing starch into the 10 cmï¿½ measuring cylinder.

7. Pour all the liquids into the 100 cmï¿½ 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 cmï¿½ of potassium iodide and 40 cmï¿½ of sulphuric acid into the 100 cmï¿½ measuring cylinder and also 5 cmï¿½ special of indicator.

12. Pour 15 cmï¿½ of hydrogen peroxide into the 50 cmï¿½ measuring cylinder.

13. Pour 10 cmï¿½ of water into the 10 cmï¿½ measuring cylinder.

14. Pour all the liquids into the 100 cmï¿½ 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 cmï¿½ of potassium iodide, 40 cmï¿½ of sulphuric acid and 5 cmï¿½ of special indicator into the 100 cmï¿½ measuring cylinder.

18. Pour 15 cmï¿½ of hydrogen peroxide into the 50 cmï¿½ measuring cylinder.

19. Pour 10 cmï¿½ of water into the 10 cmï¿½ measuring cylinder.

20. Pour all the liquids into the 100 cmï¿½ 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 cmï¿½ of potassium iodide, 40 cmï¿½ of sulphuric acid and 5 cmï¿½ of special indicator into the 100 cmï¿½ measuring cylinder.

24. Pour 15 cmï¿½ of hydrogen peroxide and 25 cmï¿½ of water into the 50 cmï¿½ measuring cylinder.

25. Pour all the liquids into the 100 cmï¿½ 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 cmï¿½ of potassium iodide, 40 cmï¿½ of sulphuric acid and 5 cmï¿½ of special indicator into the 100 cmï¿½ measuring cylinder.

31. Pour 15 cmï¿½ of hydrogen peroxide and 30 cmï¿½ of water into the 50 cmï¿½ measuring cylinder.

32. Pour all the liquids into the 100 cmï¿½ 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.

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 cmï¿½, hydrogen peroxide 15 cmï¿½ and the special indicator containing starch at 5 cmï¿½. These values were kept the same to determine the factors which affect the rate of oxidation of acidified potassium iodide solution by hydrogen peroxide. I changed the amount of potassium iodide added to each solution.

To ensure a fair test I kept the temperature constant. A higher temperature means there will be more collisions per second therefore the reaction will take place at a faster rate. There will be more collisions per second because the particles will have more activation energy which is required to break the initial bonds. If the temperature was low then there will be fewer collisions per second therefore the rate of reaction will be slower. There will be less collisions per second as the particles colliding will have less activation energy needed to break the initial bonds therefore the reaction will be slower.

Preliminary results

Volume of KI (in cmï¿½)

Volume of H2SO4 (in cmï¿½)

Volume of H202 (in cmï¿½)

Volume of special indicator (in cmï¿½)

Volume of H2O (in cmï¿½)

Time (in seconds)

The variable I intend to cover is potassium hydroxide. My maximum value is 40 cmï¿½ this reaction should prove to be a fast reaction. My minimum value is 10 cmï¿½ this should prove to be a slow reaction. My preliminary results show that my maximum and minimum values will allow more than 60 seconds between my slowest and fastest result. I intend to take five readings and repeat the experiment once.

The solutions I am going to use are:

Solution 1

40 cmï¿½ KI, 40 cmï¿½ H2SO4, 15 cmï¿½ H202, 5 cmï¿½ Special indicator.

Solution 2

30 cmï¿½ KI, 40 cmï¿½ H2SO4, 15 cmï¿½ H202, 5 cmï¿½ Special indicator and 10 cmï¿½ H2O

Solution 3

25 cmï¿½ KI, 40 cmï¿½ H2SO4, 15 cmï¿½ H202, 5 cmï¿½ Special indicator and 15 cmï¿½ H2O

Solution 4

15 cmï¿½ KI, 40 cmï¿½ H2SO4, 15 cmï¿½ H202, 5 cmï¿½ Special indicator and 25 cmï¿½ H2O

Solution 5

10 cmï¿½ KI, 40 cmï¿½ H2SO4, 15 cmï¿½ H202, 5 cmï¿½ Special indicator and 30 cmï¿½ H2O

Safety

SAFETY GOGGLES SHOULD BE WORN FOR THE DURATION OF THE EXPERIMENT IN CASE ANY LIQUIDS COME INTO CONTACT WITH THE EYES. IF SO IMMEDIATLEY RINSE YOUR EYES USING THE EYE WASH STATION. DO NOT EAT OR DRINK ANY SUBSTANCES.

Spillages should be reported to your teacher and mopped up. Breakages should be reported to your teacher. Stools must be placed under desks at all times when carrying out the experiment. Blazers must be removed when performing the experiment. The experiment must be performed standing up, this is to prevent bodily harm. Standing up allows the possibility of avoiding any liquid coming into contact with the body.

Prediction

I predict the greater the volume of potassium iodide in solution, the faster the reaction will take place. The smaller the volume of potassium iodide in solution, the slower the reaction will take place. If the volume of potassium iodide in solution is doubled, then the time taken for the reaction should reduced by twice as much. I predict the rate of the reaction will increase as the volume of potassium iodide increases.

Concentration will affect the experiment as the more concentrated the solution, the more particles of reactant there are knocking about between the water molecules which make collisions between more important particles more likely. The less concentrated the solution, the fewer reactant particles are colliding between water molecules which makes the collisions between the important particles less likely.

Temperature will affect the experiment as the higher the temperature, the faster the particles will move therefore more movement equals more collisions. The lower the temperature the slower the particles will move therefore less movement equals fewer collisions. Faster collisions will increase the rate of the reaction. At a higher temperature there will be more particles colliding with activation energy required break the initial bonds therefore the rate of the reaction will be faster. At a lower temperature there will be fewer particles colliding with activation energy required to break the initial bonds therefore the rate of the reaction will be slower.

The apparatus I intend to use is suited to the experiment and will provide accurate and reliable measurements. The method I intend to follow is simple and easy to understand, allowing maximum achievement.

Results

Solution

Volume of KI (in cmï¿½)

Volume of H2SO4 (in cmï¿½)

Volume of H202 (in cmï¿½)

Volume of special indicator (in cmï¿½)

Volume of H2O (in cmï¿½)

Time (in seconds)

1st / 2nd

Averages (in seconds)

Rate

1/time

26 / 23

24.5

0.041

44 / 41

42.5

0.024

34 / 34

0.029

58 / 61

59.5

0.017

140 / 138

139

0.007

Analysis

My results show as the volume of potassium iodide in solution increases the rate and speed of reaction increase also. My rate and time graphs also show this. The rate line – graph shows a straight line passing through the origin. The 30 cmï¿½ volume appears to be slightly strange. The rate of this volume should have been much higher as the 25 cmï¿½ volume had a rate of 0.029. This result is anomalous. The rate of reaction should have been higher as the volume of potassium iodide was higher. More concentrated solutions have more particles of reactant colliding between the water molecules which make the important collisions more likely. The lower the volume of the independent variable potassium iodide, the slower the reactions take place. Less concentrated solutions have fewer particles of reactant colliding between water molecules which make the important collisions less likely. As the independent variable increased the dependant variable decreased and as the independent variable decreased the dependant variable increased. My time graph showed as the volume of solution increased, the faster the reaction took place. The 30 cmï¿½ volume again appeared to be an anomalous result. The reason for this is explained above.

I conclude that some of my prediction matched my results. I predicted the greater the volume of potassium iodide in solution, the faster the reaction would take place. The smaller the volume of potassium iodide in solution, the slower the reaction would take place. If the volume of potassium iodide in solution was doubled, then the time taken for the reaction would reduced by twice as much.

The first part of my prediction proved nearly the same as my results however the second part of my prediction was not proven by my results. The dependant variable (time) decreased as the volume of potassium iodide in solution increased. The dependant variable increased as the volume of potassium iodide in solution decreased.

This is because the concentration of the solution increases the number of collisions per second. If the solution of potassium iodide is more concentrated, it will have more particles of reactant colliding between the water molecules. This will increase the likelihood of collisions, between more important particles. If the solution of potassium iodide is less concentrated, it will have fewer particles of reactant colliding between the water molecules. This will decrease the likelihood of collisions, between important more important particles.

The constant temperature of the 100 cmï¿½ beaker may also have affected the dependant variable. If the temperature of the beaker was high then the speed of the particles would increase therefore their moving at a faster pace so more collisions will occur. If the temperature of the beaker was low then the speed of the particles would decrease therefore their moving at a slower pace so fewer collisions will occur.

My results were not precisely the same as my prediction. If they were precisely the same my time graph would have been a perfect curve. Starting with the slowest times and finishing with the fastest times of the reaction. However it was not a perfect curve therefore my prediction was not exactly the same as my results although it was quite close. My results were very close to my prediction apart from some anomalous results. The rate graph showed the rate of reaction increased as the volume of potassium iodide increased and the rate of reaction decreased as the volume of potassium iodide decreased. The time graph showed the time of the reaction decreased as the volume of potassium iodide increased and the time of the reaction increased as the volume of potassium iodide decreased.

The second part of my prediction did not prove to be accurate, as the volume of potassium iodide was not inversely proportional to the time taken for the reaction. If my prediction was the same as my results then solution two should be directly proportional to solution four and my time graph should show that solution two is double solution four. This part of my conclusion does not support my prediction.

Evaluation

The procedure used to carry out the experiment proved to be excellent, although the only problem was trying to establish the end point of the experiment. This proved to be slightly difficult.

To improve the method the solution could be monitored by a computer to determine the end point. This method would be much more accurate than my method. The end point was hard to distinguish as the colour of the solution changes from colourless to blue/black very quickly and the black cross is still visible at certain points when the blue/black colour has formed. This method would also show the temperature of the solution, enabling a comment to be made on the speed of collisions occurring per second in solution. This method would be much more accurate as the computer would produce precise readings and almost perfect or perfect results.

The computer could be used to measure the colour/ intensity change of the solution, as the solution changes the end point could be established. The use of the computer could be improved after the preliminary experiment if any changes need to be made. I would investigate the same variable, the volume of potassium iodide however I would simply improve my method using computer technology to provide more accurate results.

My results provided quality evidence to support my prediction and conclusion. My graphs however show one anomalous result. This result was the time taken to react 30 cmï¿½ of potassium iodide. This result did not fit the general pattern. The general pattern being as the volume of potassium iodide increased the rate of the reaction decreased and as the volume of potassium iodide decreased the rate of reaction increased. The 30 cmï¿½ volume result increased instead of decreasing.

My repeated results were all within ten percent of each other. My repeated results were very similar to the first set of results I collected. My method proved to be simple and easy to follow. The range I chose was an excellent range which provided accurate results apart from one anomalous result. Four out of my five results were accurate, that’s eighty percent accuracy therefore my results are quite accurate.

To improve my results I could repeat the experiment four times instead of two. I could wash the apparatus with teepol before and during the experiment to provide more accurate results. The advantage of using teepol is any substance residue remaining in the beakers of measuring cylinders is removed. I could use a wider range of solutions. To improve the experiment I could use a conical flask and a pipette. The conical flask would be used instead of the 100 cmï¿½ beaker. This would be easy to swirl instead of stirring the solution. Instead of using measuring cylinders to measure specific amounts of substances, a pipette would provide more accurate measurements. The method would be the same, the only difference would be the solution would be contained in a conical flask and the volumes would be measure by using pipettes.

My results provided sufficient evidence to support my conclusion. The only problem with my results is, human error is an obviously possibility. My results prove my conclusion, as the volume of potassium iodide increases the time of the reaction decreases and as the volume of potassium iodide decreases the time of the reaction increases. The rate of reaction increases as the volume of potassium iodide increases and the rate of reaction decreases as the volume of potassium iodide decreases.

The anomalous result of 30 cmï¿½ of potassium iodide may have occurred because of the water left in the measuring cylinders after they had been washed, this may have affected the outcome of the solution. The measuring cylinders and the beaker were only washed with water, they were not rinsed with teepol, and residue from other substances may have remained in the beaker or measuring cylinders maybe explaining why this result was anomalous.

Excluding this result my time – volume graph would have been a perfect curve. I think the line of best fit on this graph is correct but not precisely accurate. If all my results were as expected then the line would have been a perfect curve as I stated above. My results were very close to my lines of best fit. The line of best fit on the rate – time graph was very close to all of the results. I am very sure of this line of best fit. All the results are very close to either side of the line.

My results are reliable but not one hundred percent reliable. If a computer was used in this experiment then the results would be very close to one hundred percent accurate. My results are approximately seventy percent accurate as they were all in ten percent of each other and four out of the five results matched the pattern I described in my conclusion.