Kera PezzutiPer. 4

In this lab, we observed the effect of varying times in a reaction involving an enzyme called catalase. Before we could get to the actual lab, several values needed to be obtained that would be important during the calculations of the reaction. First, we observed the reaction to be created, H2O2 H2O + O2 with the assistance of catalase. In contrast, another experiment was held to determine the rate of hydrogen peroxide decomposition spontaneously. “Spontaneous” means that the solution will be left alone for twenty-four hours and the reaction will occur without any enzymes. Also to be determined was the baseline—an index of the initial concentration of hydrogen peroxide in solution. This value was utilized to establish the amount of H2O2 used in the multiple timed reactions. Finally, the timed reactions were done by using the same procedure in the test of catalase activity. These solutions were allowed to progress at several times from one to six minutes. By comparing the timed reactions with the uncatalyzed reaction, we could determine the effectiveness of catalase.

First, the reaction was observed by adding 1 mL of catalase to 10 mL of 1.5% H2O2 and bubbles of oxygen were seen exiting the solution. From this we could determine the equation of the reaction, H2O2 H2O + O2, and that the enzyme was catalase. To be certain the gas that was created was water, titration similar to that done in the dissolved oxygen lab had to be performed. A very similar procedure was followed to determine the base line, but catalase was left out and replaced by H2O. 10 mL of sulfuric acid was also added to the solution. 5 mL were removed from and then titrated with potassium permanganate. This showed us the initial amount of hydrogen peroxide in the solution to be used throughout the course of the lab. In our group, we came up with a baseline of 3.8 mL of potassium permanganate that was needed to change the color of this solution.

We determined the rate of spontaneous conversion of hydrogen peroxide to dihydrogen oxide and dioxide without catalase. In order to complete this, a small amount of 1.5% H2O2 was put in a beaker. After being left for twenty-four hours, this solution was titrated just like the baseline including adding the water, sulfuric acid, and potassium permanganate. By subtracting this new titration value by the baseline a percent of spontaneously decomposed hydrogen peroxide was found. Ours was 26.3%

In the main part of this lab, we measured how much substrate disappeared over various increments of time. To find these values, the solutions went through the same procedure, but the amount of time allowed for catalase to catalyze differed. In seven beakers, 10 mL of 1.5% hydrogen peroxide were inserted and followed by 1 mL of catalase extract. Each beaker was then swirled for a different amount of time—10, 30, 60, 90, 120, 180, and 360 seconds. After whichever increment of time, 10 mL of H2SO4 was added to stop the reaction so measurements could be made. For 10 seconds, .7 mL of hydrogen peroxide was used. For 30 seconds, .9 mL of hydrogen peroxide was used. For 60 seconds, 1.8 mL of hydrogen peroxide was used. For 90 seconds, 2.1 mL of hydrogen peroxide was used. For 120 seconds, 2.2 mL of hydrogen peroxide was used. For 180 seconds, 2.0 mL of hydrogen peroxide was used. For 360 seconds, 1.3 mL of hydrogen peroxide was used.

Although some of our data breaks the mold, the general trend is that more substrate is converted as the time goes on. By comparing the uncatalyzed reactions to the solutions that included catalase, it was evident the enzyme had a great impact on the progress of the reactions. Through all the different solutions created and titrated in this lab, one can conclude that time is a great factor in the progress of a reaction and that enzymes make a remarkable difference.