Constants
- Volume/concentration of hydrogen peroxide (10cm3 of 20 vol. hydrogen peroxide + 10cm3 of water).
- Amount of each catalyst (1g).
- Time left for/intervals at which gas is measured (every 5 seconds for 50 seconds).
- Same general apparatus.
NB. Wash apparatus after each experiment.
Measurements
The volume of gas (oxygen) produced will be measured during each test at 5-second intervals- this will be done by measuring how much water is displaced in the measuring cylinder by the gas. Each catalyst will be tested twice, and the test will last for 50 seconds on each occasion.
Results
Average rate of reaction
Average rate= volume/time=…..cm3/sec
Manganese dioxide= 96/40= 2.4 cm3/sec.
Copper oxide= 27/50= 0.54 cm3/sec.
Iron dioxide= 27/50= 0.54 cm3/sec.
20 vol. of hydrogen peroxide means that each cm3 gives off 20 cm3 of oxygen gas. We diluted it to 10 vol. Using water and so we would have expected 100 cm3 of oxygen.
Hence manganese dioxide as well as being the best catalyst also caused more hydrogen peroxide to break down.
Evaluation
Although the results obtained were fairly good, there were quite a few problems during the experiment, which affected them. These were:
- It was difficult to fill the measuring cylinder with water, as well as insert it into the trough (water bath) without any escaping and creating difficulties in measuring the gas produced.
- The largest measuring cylinder was only 100 cm3. This was very relevant as one of the tests for manganese dioxide exceeded 100 cm3 in gas produced, therefore a larger cylinder was needed.
- The catalysts were very fine powders, which made it difficult to measure out exactly 1g.
- When gas was being produced and coming off fast, it was difficult to read the measurements accurately as the surface of the water wasn’t steady. (It was also difficult when a gas bubble came up while the gas volume was being measured).
In act to improve the experiment and thus make the results more accurate, the following could have been done:
- A wider measuring cylinder used so that gas being produced rapidly would not disturb the water surface as much, making the volume of gas easier to measure.
- A larger measuring cylinder used so that gas volumes exceeding 100 cm3 could be measured and therefore the results not interrupted with.
- Repeat testing (i.e. 3 tests for each catalyst) carried out so that there is less room for error whilst obtaining results. This would also make them more reliable.
When the results were obtained, there were some noticeable abnormalities i.e. anomalous results. These were; the measurement of gas after 5 seconds when testing iron dioxide, and the tests when using manganese dioxide. This was because when manganese dioxide was being tested, there were large differences in measurements at each time interval, therefore experimental errors must have occurred (after 40 seconds on the first test, the gas volume also exceeded 100 cm3, whilst in the second test this did not happen until after the 50 second limit). The other anomalous result was when testing iron dioxide, as after the first 5 seconds, there was a large difference in the volume of gas between the 2 tests carried out (30 cm3 : 20 cm3). The cause of these anomalous results is most likely related to the surface area of the catalyst in correlation with each test carried out i.e. the powdered catalyst may have been slanted up the boiling tube during one test, but not on the other, resulting in different surface areas. Shaking the boiling tube before each test and/or using a wider testing tube, could have however prevented this.
From the results obtained, you can also not definitely state the best catalyst for his reaction, as all 31 transition metals were not tested. Therefore to extend this investigation to find the best catalyst for producing oxygen gas from hydrogen peroxide solution, all the transition metals could have been tested as well as repeat tested for verification. This, in conclusion, would have found the best catalyst for this particular reaction.
