Enzyme Lab

Purpose

    In this lab we are observing the concentration of Hydrogen Peroxide (H2O2) in water and oxygen gas by the enzyme catalase. Then we are going to measure the amount of oxygen generated and calculate the rate of the reaction. Also, we will observe environmental factors such as pH and temperature changes.  

Introduction

   Enzymes are proteins that can speed up or slow down reactions. They are known as catalysts in reactions. Enzymes are the only thing not changed throughout the reaction. Enzymes can become denatured due to heat and pH changes. When they are denatured the enzymes become biologically inactive. Enzymes have specific duties and their active sites interact with certain substrates.

Methods

Part 2B: In this part, we put 10 mL of a 1.5% H2O2 solution in a clear plastic cup and added 1 mL of water, then 10 mL of 1 M H2SO4 solution, using a 1 mL and 10 mL syringe respectively. We mixed the resulting solution, then took a 5 mL sample of it and placed it in a separate clear plastic cup. Using a burette, we titrated the sample drop by drop with a 2% KMnO4 solution until the sample turned pink then brown and measured the amount of KMnO4 had been used.

Part 2C: In this part, we followed the same procedure as part 2A, but used a sample of 1.5% H2O2 solution that had been decomposing for 24 hours instead of the fresh 1.5% H2O2 solution.

Part 2D: In this part, we followed the same procedure as part 2A, but instead of the 1 mL of water, added 1 mL of a yeast solution that acted as a catalase to the H2SO4. We allowed the mixture to sit for 10 seconds  for reactions to occur before titrating a 5 mL sample. We then repeated the process seven times, allowing the reaction to be catalyzed for each of 30, 60, 90, 120, 180, and 380 seconds before titration.

Data

Graphs & Charts

Discussion

Part 2B: The initial reading of the burette was 13.5 mL. After completion of the experiment, the burette’s reading had dropped down to 10 mL. The baseline was calculated by subtracting the initial reading from the final reading, giving us the result of 3.5 mL of KMnO(4). This means that the initial amount of H(2)O(2) present in the 1.5% solution was also 3.5 mL. The other two groups in our class had results ranging from 3-4 mL so it’s safe to say that our results were rather valid. To ensure results, it’s never a bad idea to redo a baseline but in this case we didn’t see any reason to have to do so.

Part 2C: The initial reading of the burette was 26.5 mL and and after the completion of this experiment, the burette reading was at 31.0 mL. This resulted in 4.5 mL of KMnO(4) titrant used. Therefore, the amount of H(2)O(2) spontaneously decomposed (mL baseline-mL KMnO(4)) was 1.2 mL. The percent of the H(2)O(2) that spontaneously decomposes in 24 hours [(mL baseline-mL 24 hours) / mL baseline] x100 was approximately 3.5%.

Part 2D: Before starting the experiment, we once again conducted a baseline with the result this time being 3.3 mL of H(2)O(2) being present in the 1.5% solution. This was still in the range that most other groups were getting so there was no concerns with that. Even if the change had been slightly greater than that what we got the day before, it wouldn’t have caused much alarm because it was expected that some chemical changes may have taken place in the bottle that held the solution with it being constantly opened and closed. For both my sake and the reader’s, I will now direct you to look at the table above with all our data for this experiment, rather than me typing it all out once again. The biggest trend seen here is that there is an inverse relationship between the amount of KMnO(4) consumed and the amount of H(2)O(2) used. As the time given for the reaction to occur increases, the amount of KMnO(4) consumed decreases while the amount of H(2)O(2) used increases. The results obtained were within the range that we were looking for as well as the inverse relationship I just mentioned. We definitely ran into a little error the first time we tested the 30 sec reaction because the results we obtained did not match the pattern seen in the other experiments, but it was easily solved by simply redoing that one, so we strongly suggest to anyone else doing these experiments to keep the solution samples until you are 100% satisfied with the results you obtain :)

Conclusion

In summary, we learned the importance of conducting a baseline and that the amount of KMnO(4) used also represents the initial amount of H(2)O(2) in the 1.5% solution. Also, if you let a solution of 1.5%H(2)O(2) stand for 24 hours, a portion of it will spontaneously decompose. The most important thing that we got out of this those, is the concept that the longer an enzyme has to do its work, the more it can produce in form of the desired reactions.