Using the information I already know about the rate of decomposition of hydrogen peroxide (see above equations) I can predict that the larger mass of catalyst (which will be manganese oxide MnO2) the quicker the rate of decomposition. It is also because to increase the rate of a reaction you need to increase the number of successful collisions. One possible way of doing this is to provide an alternative way for the reaction to happen which has a lower activation energy. A catalyst provides an alternative route for the reaction. That alternative route has lower activation energy.
To carry out the experiment I will need the following equipment:
- Balancing scales
- Manganese Oxide
- Hydrogen peroxide
- A clamp
- A 100cm³ syringe
- Six boiler tubes
- A boiler tube rack
- A delivery tube going into a rubber bung
- A spatula
- Six small dishes
- A stopwatch
- A pen and paper
I decided to measure masses of 0.1g, 0.2g, 0.3g, 0.4g, 0.5g and 0.6g of MnO2 using balancing scales. I measured these amounts into six small dishes using a spatula. I then poured 20cm³ of hydrogen peroxide into each boiling tube and placed the six boiling tubes in a boiling tube rack. I then placed the syringe in the clamp and put the delivery tube going into a bung in the syringe (see diagram below):
I then very quickly put the manganese oxide into the boiling tube filled with 20cm³ of hydrogen peroxide and put the bung into the boiling tube (see above diagram). I then timed every 10 seconds with a stopwatch and at every 10th second I measured the amount of oxygen that had gone into the syringe. I noted the results down on paper using a pen. I was going to repeat the experiment in order to get averages and make my results more reliable, but I ran out of time.
To make the experiment fair I only changed one factor. I also made sure I only started timing once the test tube was attached to the syringe. There were no gaps for oxygen to seep in, making the test a fair one.
Results
See graph on next page…
Conclusion
From my results table and my graph I can see that the larger mass of catalyst (MnO2) the quicker the hydrogen peroxide decomposed. I can also see that as time goes on the decomposition becomes slower. This is shown on my graph by the lines gradually getting steeper and the points getting closer together as time goes on. This could be due to a lesser amount of energy working because the catalyst is being used up. I only have one slight anomaly on my graph. This could be because I was slightly out of time or didn’t read the syringe properly. My results support my prediction. This is because to increase the rate of a reaction you need to increase the number of successful collisions. The way I did this was to provide an alternative way for the reaction to happen which has a lower activation energy. A catalyst provides an alternative route for the reaction. That alternative route has lower activation energy.
Evaluation
I think my experiment went well. I made no huge errors, but I could improve on the timing of getting the manganese into the boiling tube and putting the bung in. Several times I did not push the syringe back into the original place, so I had to re-weigh and perform the experiment for that particular mass of catalyst. This took up some time. I may have been slightly inaccurate in measuring the amount of oxygen collected in the syringe. This is because you have to look at the stopwatch as well as the measurements on the syringe, which can be hard. Therefore I could have made my results inaccurate by only a couple of cm³. To improve the experiment I could repeat the experiment three times and work out an average for each amount of catalyst. This would make my results more reliable. I could also do the experiment with other people so that one can time, one person could read and another could write down the results. This would make my results more reliable. It would also be a good idea to use a syringe that can hold more than 100cm³ because I could see how long it took to actually stop decomposing, improving my results. To further my work I could repeat the same experiment using different catalysts such as copper oxide or iron oxide and see if they worked better at decomposing the hydrogen peroxide quicker.
