Investigation of a Factor Affecting the Rate of Hydrogen Peroxide Decomposition

  • Light intensity kept the same as light intensity changes the decomposition of hydrogen peroxide, as it is light sensitive.

Materials:

• 150mL of hydrogen peroxide
• 250mL conical flask
• Stopper
• Gas carrying tube
• Manganese oxide (catalyst)
• Watch glass
• Electronic balance
• 50mL measuring cylinder
• 100mL measuring cylinder
• Bucket
• Thermometer
• Spatula
• Water
• Retort stand
• Clamp
• Boss head
• Stopwatch

Method:

1. Put on all precautionary safety gear.
2. Half fill the bucket with water.
3. Fill the 50mL measuring cylinder with water, cover the end and invert into the water. Make sure that the end of the inverted measuring cylinder is in the water in the bucket so that it cannot come out. Hold the measuring cylinder in place using a retort stand, boss head and clamp.
4. Put the gas carrying tube through the hole in the stopper so that around two centimetres is showing out of the bottom. With the other end of the tube cover the end, so that no water gets in the tube, and place in the bucket of water going up through the measuring cylinder so that the end of the tube is facing the bottom of the inverted measuring cylinder, release the cover of the tube.
5. Whilst wearing gloves measure out 2mL of hydrogen peroxide into the 10mL measuring cylinder and add 8mL of distilled water and mix.
6. Empty contents of the measuring cylinder into the 250mL conical flask and measure the temperature.
7. Measure out 0.1 grams of catalyst (manganese oxide) on the watch glass with the electronic balance.
8. Add the catalyst to the conical flask, put the stopper in the top tightly and have another person start timing when the catalyst is added. All of this should be done in as short a time as possible to prevent inaccuracies in the readings.
9. Stop the timing when 40 mL of gas has been collected. Record the time that this takes.
10. Repeat Steps 2-8 using 2mL more of hydrogen peroxide and 2mL less of distilled water each time until the mixture is completely hydrogen peroxide. Make sure that the temperature and the amount of the catalyst remain the same throughout the experiment.

2. Presentation:

Results:

Table 1: Time taken for 40mL of gas to be collected when changing the concentration of hydrogen peroxide.

3. Conclusion and Evaluation:

Discussion:

  The first graph has a fairly high R2 value of 0.9537. However, a couple of he points on the graph are a fair way out from the line of best fit suggesting some random error in these points. Random error in these points could have been caused by human error. The second graph suggests a large systematic error. Because although the points are fairly close to the line, suggesting they are reasonably precise, the graph does not pass through the origin like it should suggesting a systematic error. The systematic error could be due to some of the hydrogen peroxide decomposing in the atmosphere before the catalyst can be added.

  The rates are determined as an average. This is because the rates are checked as the amount of the time it takes to collect 40mL of gas. The measurement of time is done from start to finish not at intervals in between like would be done for an instantaneous rate to be determined.

  The graphs above suggest that as the concentration increases the time that it takes to collect 40mL of gas gets smaller. This supports the hypothesis made. The rate of this reaction must increase when concentration increases, as this will cause more frequent collision between molecules. The graphs definitely suggest this as when the concentration increases it takes a far shorter amount of time to obtain 40mL of gas from the reaction. Because the results are fairly precise this conclusion can be drawn from the graphs.

  There are some improvements that could have been made to the procedure. One of these was that because the conical flask was fairly large in comparison to the amount of hydrogen peroxide put in there it took quite a while for gas to begin to displace the water from the bucket. This time that it took for the conical flask to fill with gas distorted the results and meant that not all f the gas produced by the reaction went into displacing the water and the results therefore were not as accurate as they could have been. A way that this could be fixed is by using a smaller conical flask so that the gases produced will go much more quickly through the tube and displace the water. It was also very difficult to transfer the catalyst from the watch glass to the solution in the conical flask. This was because some of the manganese oxide would stay on the watch glass and due to its shape it made it difficult to make sure that all of it has gone into the mixture. Because the amount of catalyst was very small loosing some of it could have made a very large difference to the results obtained. This problem could have been fixed by using a funnel to convert all of the catalyst from the measuring apparatus to the hydrogen peroxide. Another problem was with the time delay of putting the stopper into the top of the flask after the catalyst had been added. This time delay meant that some of the gas might have been able to escape thus changing the results. The time delay between this could have been minimised by using a conical flask that had a hole in the side of it that could be covered so that the stopper could already be in and then the catalyst could be put in and the hole covered immediately after. This process would be a lot less difficult as it is a lot easier to place the cover over the hole than it is to put on the stopper whilst making sure that the tube does not come out of the inverted measuring cylinder.