Method for collecting data:
- Mark all test tubes that are used that are used in this experiment at one same point, being the top of the test tube.
- Weigh out 0.15g of yeast on the electronic weighing scale by firstly putting the Petri-dish on the scale and setting the scale to zero so that the mass of the Petri-dish doesn’t count with the mass of yeast.
- Deposit the 0.15g of yeast in one of the test tubes and place the test tube on the test tube holder.
- Out of the five concentrations of Hydrogen Peroxide; measure out 3ml of any concentration (except the 0%) by pouring it in the measuring cylinder which should be measured at eye level.
- Pour the 3ml of Hydrogen Peroxide of that specific concentration in the test tube containing yeast, and start the stopwatch at the same time.
- Bubbles should start rising up the tube and as soon as it reaches the top of the test tube where the mark is, stop the stopwatch.
- Note down the time taken for the reaction to reach the mark and the appearance of the reaction.
- Repeat the same experiment with the unchanged concentration and amount of Hydrogen Peroxide and yeast at least two more times.
- Use the same steps to find out the time taken for the reaction to reach the top of the test tube with the remaining five concentrations.
- For the concentration of Hydrogen Peroxide being 0%, 3ml of distilled water will only be used because to decrease the concentration of Hydrogen Peroxide, distilled water is added.
- Repeat the same steps for this concentration too and note down the quantitative and the qualitative results.
Data table:
Time taken for the reaction to reach the top of the test tube at the marked point:
From these results I was able to plot a graph for the time taken for the reaction to reach the marked point on the test tube against concentration of Hydrogen Peroxide:
Data processing:
Conclusion:
As it was hypothesized, the rate of reaction did increase as the concentration of Hydrogen Peroxide was made higher, and so the time taken for the reaction to reach the top of the test tube decreased. This would be because as the concentration of the substrate solution increases while the concentration of the enzyme remains the same, the substrate-active site collision will increase and the reaction will take place much faster. This pattern can easily be noticed on both the raw and the processed data tables.
On the processed data table, we can see that as the concentration of Hydrogen Peroxide increases, the average time taken for the reaction to reach the marked point on the test tube decreases since the reaction took place much faster.
By looking at both the tables and the graphs, it can be seen that there is a sharp increase in the slope and the values for the time taken between concentrations of 3% and 6%. The difference between the times taken from 6% concentration to 10% concentration is much smaller compared to the first one but the time taken between the concentration of 10% and 15% is the smallest.
After 10% the increase in the rate of reaction slows down and if it was tested further then 15%, then most probably a constant value would be obtained. At this point virtually all the active sites would be occupied so the active sites are said to be saturated with Hydrogen Peroxide. Increasing the Hydrogen Peroxide concentration after the point of saturation will not cause the rate of reaction to go up any more. All the active sites are being used so any extra Hydrogen Peroxide molecules will have to wait until an active site becomes available.
Evaluation of limitations and weaknesses:
This experiment was done as precisely as possible so as to obtain the most correct results for each test. In order to keep this experiment accurate, each test was repeated three times and an average of the results obtained was found. All the variables except the concentration of Hydrogen Peroxide were kept constant but in reality, it is physically not possible to keep all the variables precisely the same due to some of the random and systematic errors. For example:
- It would be difficult to start the stopwatch exactly when the Hydrogen Peroxide is poured into the test tube containing yeast and therefore the stopwatch would either have started before pouring or after pouring.
- It is also impossible to precisely measure out the amounts of Hydrogen Peroxide of different concentrations because it is a systematic error and is caused by the way and the direction from where an individual is measuring.
- The amount of yeast measured would also not be very accurate because on the electronic weighing scale, the second decimal point does keep on fluctuating and so it becomes difficult to tell whether an exact amount it obtained. This is a random error.
- Another error would have occurred while pouring the Hydrogen Peroxide into the test tube from the measuring cylinder since not all the amount would have been poured in. some amount could have remained in the cylinder while some amount could have dropped out of the test tube while transferring.
Improvements:
- This experiment could be improved in a number of ways. It could be repeated more then three times to get a more accurate result. A better overall result would be obtained by repeating the experiment more times because any errors in one experiment should be compensated for by the other experiments.
- Using more concentrations of Hydrogen Peroxide would have produced a better looking graph and I would have liked to use concentrations higher than 15% to extend the graph so that the maximum possible rate of reaction could be reached.
- The problem of starting the stopwatch at the same time while pouring the Hydrogen Peroxide could be overcome by getting another person to start the stopwatch when the Hydrogen Peroxide was poured into the tube.
- A more accurate electronic weighing scale which gives its answer in three decimal places would give a better result.