4 137 73.0
5 149 67.1
6 159 62.3
7 255 39.2
8 364 27.5
9 810 12.3
10 denatured dentaured
Once I had calculated all of the rates for each solution tube, I was able to construct the two line graphs. Looking at the graph representing time against pH, you can see quite clearly that there is a pattern. Once the results have been plotted there is a clear shape that has formed, which is most likely not a coincidence, as it must have something to do with the pH. You will notice that the solutions with pH between 1.3 and 1.7 seem to have the lowest reaction time, whereby all of the egg suspension has vanished and the solution returned to its initial clear colour. It is apparent that the solutions with a pH lower than 1.3 and higher than 1.7 are not the optimum pH, as the reaction times are much slower. Another clear observation is that a solution with pH more than 2.3 subsequently denatures, this is a slight flaw in the set-up which cleverly attempts to catch you out.
When you observe the graph showing the rate against pH, another clear trend is apparent, where the shape of the line is very similar to that of the one in the first graph. The curve this time though is the other way around, this must have something to do with the conversion of time into the rate. It shows that the pH between 1.3 and 1.7 is has the highest rate of reaction, meaning that it is a quicker reaction. The solutions with a pH either side of 1.3 and 1.7 have lower rates, meaning a slower reaction. Although looking at the graph more closely, it is apparent that the optimum pH for a reaction is 1.3, as it has the highest rate of reaction in all of those tested. From the line of best fit on both graphs, it is clear that some of the points do not exactly fit. They are anomalies. Although they have only slight inaccuracies, they are an indication of possible errors in the investigation, there could be many reasons for this, for example, maybe I measured out the acid to a slight differential volume than was expected, but these things are only minute. As long as you can see the general pattern that arises, then a general conclusion can be formed. The measurement of the time taken for all of the egg suspension to disappear is probably the most likely to cause an interference in my final results. Another example could be that there was a slight temperature fluctuation which could have caused the reaction rate to increase slightly.
There are some suggestions and improvements which can be made, and these are for example, to procede with only one solution at a time, this would make the overall experiment much slower, but you would be able to obtain better and more reliable results, especially when you have the chance to concentrate on one tube in the water bath, making the time taken for the reaction to take place much more reliable. This will ultimately reduce the amount of errors in the investigation to a substantial degree. I could also carry out the same experiment five or more times, and recall and mean, to observe whether or not there were any abnormal results in the first attempt.
The dependant variable was the pH, which was already decided for me before I continued with the task. The independent variable was the time taken for the reaction to happen, as this was not known until the experiment was finished. The independent variable was what I was initially trying to discover.
If I was to predict an hypothesis for this experiment, then it would include that the rate of reaction would be at its highest or optimum, at a specific pH concentration. But I would not have known what that pH would have been as I did not have any references, and that was what I was finding out anyway.
The rate of reaction must have also been greatly influenced by the enzyme, which in this case is pepsin. The pepsin concentration was at a constant so there is another test which could be explored, whether different concentrations of the enzyme would have an effect. Although it would be expected that an increase in enzyme concentration would result in an increase in the rate of reaction. It is on the active site of the egg suspension where the pepsin locks onto, making it easier for the reaction to occur. This bind is called an enzyme – substrate complex. The reaction then takes place and the product leaves the enzyme. The enzyme, unchanged by the reaction, can then be used again: enzyme + substrate – enzyme-substrate complex – enzyme + product.
It was noticeable that in the final solution in the experiment, the enzyme had denatured, resulting in there being no change in the solution. Enzymes, like other proteins consist of polypeptide chains held together in a particular position by cross-links. When an enzyme is dentaured, the cross-links are broken and the polypeptide chains open up and become randomly arranged. As a result the protein loses its normal shape and becomes biologically inactive. Dentauration is brought about by heating, excessive amounts of certain chemicals, or in this case but extremes of pH.
Overall it has been proven that there is a particular pH which is 1.3 in this case, it may be slightly either side of this, so that in itself is a minor error, which provides us with the optimum rate of reaction. The results are generally quite reliable, the procedure was of a good standard for experimentation, although the experiment could have been carried out a few more times to ensure fairness and an average reaction rate. Obviously there is also the bug in the set-up, which is the denaturation of solution ten. This is something which can be recorded and then adjusted to find out what the highest pH the reaction will occur at. I have gained from this experiment and will have a better understanding for future references.
DUNCAN BEARD
