This was done by filling a beaker with tap water; it was filled with enough water so that when the full burette was able to be inverted into it with the water above the mouth of the burette. The burette was carefully clamped so that its markings pointed to the front and could be seen clearly. The delivery tube was inserted into the mouth of the burette and connected to the conical flask. The hydrogen peroxide solution is poured into the conical flask and then the Catalase solution is added. The bung is immediately placed over the conical flask and the stop clock started.
The reaction was timed for five minutes and the volume of oxygen produced recorded every sixty seconds. After the first experiment, the contents of conical flask were carefully tipped into the waste container. The conical flask was rinsed and the apparatus set up again. Results: After the results were recorded in the table, averages of the results were taken. The average for each hydrogen peroxide concentration, for the volumes produced within the sixty-second intervals was calculated by adding the two results up and then dividing their answer by two.
This was then recorded in the third column for each concentration in the table. H2O2 Conc. (ml) Volume of oxygen (ml) Observations: Vigorous bubbles were observed inside the conical flask at the start of the reactions, especially with the higher hydrogen peroxide concentrations. The rate of bubbles entering the burette decreased as the reaction continued.
As the concentration of hydrogen peroxide was decreased the produced bubbles decreased. One of the problems that were met in the experiment can be seen in the results for the 1M test. The results for that concentration should have in theory decomposed the hydrogen peroxide at a faster rate than 0. 8M, but the problem was that it became difficult to replace the bung without letting any oxygen be released. Unlike in the other tests were the rate of reactions is slower allowing the return of the bung without releasing enough oxygen that would impact the results. Analysis:
The results in the table above allow us to plot a graph to show the initial rate of reaction, and how it changed according to the concentration of the hydrogen peroxide. The graph above clearly shows that the rate of reaction decreases almost proportionally to the decrease in hydrogen peroxide concentration. This graph show the rate of reaction by the equation:- Rate = Oxygen produced / Time. This graph more clearly shows the anomalous result in the concentration 1M, since it should have had a higher production of oxygen volume. Evaluation: Criticisms of the method:
The main problem with the method stated earlier is that the bung is not replaced earlier enough when the concentration of the hydrogen peroxide is too high. The problem is that too much oxygen is leaked before that bung is put back to seal the conical flask. Hydrogen peroxide is measured in Vol’s not moles. This could cause the results to be inaccurate as to the usual behaviours of a 1 mole concentration. When using a pipette some times an air bubble may get in the way, and it isn’t always possible to remove them, like when measuring hydrogen peroxide where there are health risk precautions that need to be taken.
The timer may have been started a little late due to human reaction time, and also in the cases where the concentration of hydrogen peroxide is high there wasn’t always enough time to start the timer and put the bung on the top of the conical flask at the same time, this caused some timing errors. Improvements: Clean all equipment that needs to be used thoroughly before use. More repeats need to be taken to obtain more accurate results. Investigate with more variables like, the concentration of Catalase or temperature.
Percentage error:Percentage error = (error / measurement taken) x 100 Maximum error calculated Thermometer – error = i?? 0. 05i?? C (0. 05 /30) x 100 = 0. 1667% Burette – error = i?? 0. 1ml (0. 1/14. 4) x 100 = 0. 694% Pipette – error = i?? 0. 1cm3 (0. 1/0. 2) x 100 = 5% Timer – error = i?? 0. 005s (0. 005/60) x 100 = 0. 0083% Total = 5. 869% error.
Bibliography: Chemical Ideas, Salters Advanced Chemistry A-level Chemistry, Ramsden http://www. chemsoc. org/networks/learnnet/cfb/enzymes. htm Biology, Collins Educational Chemistry in Context, Nelson.