Procedures
1. Add 20cm3 of H2O2 in to a baker. (for each trial)
2.Decide the number of drops of acid, base or water to be used as a standard through out the experiment to change the pH of the substrate so as to investigate the effect of catalase at different pH values i.e. decide the total number of drops added through out the experiment to be 12 drops. For example, if you use 9 drops of HCl add 3 drops of water to keep the total number of drops used constant i.e. 12 drops.
3. Add 0.5ml of the blundered liver to the baker containing H2O2 and the chemicals used to get the value of pH required.
4. Close the baker immediately after you add the blundered liver with the cork and connect it to the gas syringe using a small tube and record the volume of gas produced in the reaction.
Table of results:
Discussion
In this particular experiment we have used the same amount of H2O2 (20 ml) and blundered liver (0.5 ml) that contains naturally made catalase produced by liver cells through out the experiment but we had to change the pH level by varying number of drops of NaOH base, HCl acid & H2O in each trial as indicated above in the table of results.
Though I do not dare to say our experiment is quite precise as it should be we could get a result which is very close to the theoretical ideal pH for catalase. We could prove that the activity of catalase is highest around the pH 9. From our 2nd trial we could get 121.5 cm3 of gas in average at the pH value of 9. From our 5th trail we got the average volume of 126 cm3 at the pH of 8.6. The results of these two trials confirm that catalase works best at around pH 9 because the volume of gas produced from these reactions i.e. when we let the reactions happen at this pH level is considerably higher than the rest of our trials though we have used the same amount of H2O2 and liver. In other words big amount of products can only be founded when the enzyme is active enough to activate the reaction. By contrast from trials 4 & 6 we can also observe that the activity of catalase in acidic medium is extremely low. We could only get 5.5 cm3 & 3 cm3 at the pH 1.9 & 1.7 respectively using the same amount of liver and H2O2 as we have used in the other trials. Generally we proved that the activity of catalase increases with pH up to about the pH value of 9 and drops again when the level of pH becomes higher above that level.
Conclusion: The ideal pH for catalase to work best is around pH of 9.
Evaluation
There were many things that could affect the accuracy of our result. The pH measuring device was not reliable. It was so difficult for us to record the correct pH value as the reading was changing randomly for very long time. The measuring cylinder we used to measure the volume of H2O2 and the syringe we used to measure and transfer the blundered liver have their own uncertainty. The concentration of catalase might not be the same in each trial though we have used the same amount of liver in each case as catalase might not be found evenly distributed. The gas syringe was not big enough to hold the gas produced in some cases and we had to open the baker to let out the gas from the gas syringe to make it ready to measure the remaining gas produced from the reaction. This time some amount of gas has escaped. We have used 0.5 cm3 of blundered liver but we could use even smaller amount of liver to get more accurate result since we could get lesser amount of gas that could be measured easily. The problem is the uncertainty of the syringe we have used is high and it is more difficult to measure very small amount of the blundered liver with it accurately but we could have overcome this problem if we had used a syringe with lesser uncertainty or we had use bigger gas syringe if there was. I think if we had better pH measuring device or universal indicator we could get more accurate result. If we could use burette or pipette to measure the volume of H2O2 than using measuring cylinder we could get better result since these two apparatuses have lesser uncertainty.
