Ramchandran, Renuka
Period 2
Exercise 2D: An Enzyme-Catalyzed Rate of H2O2 Decomposition
Independent Variable: The time (the seconds or the interval between adding the catalase and
adding the sulfuric acid)
Dependent t Variable: The amount of H2O2 that decomposed or was used in the reaction
Data Collection and Processing
I.
Raw Data
Establishing the Baseline
Volume (mL) (±0.1 mL)
Initial Reading
5.0
Final Reading
2.0
Baseline (KMnO4)
3.0
Amount of H202 Used At Different Time Intervals
Volume (mL) (±0.1 mL)
KMnO4 (ml)
Time (seconds) (± 0.5 seconds)
Time (seconds)
10 30 60 120
A. Baseline
3.0 3.0 3.0 3.0
B. Initial Reading
5.0 5.0 5.0 5.0
C. Final Reading
2.5 2.6 3.0 3.1
D. Amount of KMnO4 Used
2.5 2.4 2.0 1.9
E. Proportional Amount of H2O2 Used
0.5 0.6 1.0 1.1
Catalase
Titrating
180
3.0
5.0
3.4
1.6
1.4
Qualitative Data
We noticed that when we added the catalase to the H2O2 solution,
bubbles started to form in the cup showing the decomposition into the O2
that was being released.
As time interval increased, we noticed that the KmnO4 took longer to
disappear within the clear solution showing that it would require less to
reach the persistent pink, brown color.
Pictures
KMnO4 Solution used to
titrate the Catalyzed
Reaction to determine
amount of H2O2 that
decomposed.
Different Time
Intervals
Titration of
solutions with
KMnO4 solution to
determine the
amount of H2O2
that decomposed.
II.
Data Processing
The first part of the data that needed to be calculated was the baseline. For this, we titrated the
sample of hydrogen peroxide with potassium permanganate using a syringe. We then subtracted
the final reading from the initial reading to get the baseline.
Initial - Final = Baseline
5.0 mL – 1.7 mL = 3.2 mL
This baseline was then used for the rest of the calculations. After titrating the cups with
potassium permanganate in the second experiment where the hydrogen peroxide was mixed with
catalase (which follows the procedure of adding sulfuric acid to the cups after different time
intervals), the values recorded were used to calculate the amount of hydrogen peroxide that
decomposed or was used in the reaction. First, the amount of KMnO4 used was calculated for
each time interval:
Initial Reading - Final Reading = Amount of KMnO4 Used
(At 10 seconds)
5.0 mL – 2.5 mL = 2.5 mL of KMnO4 used
Next, the proportional amount of H2O2 used was calculated:
Baseline – Amount of KMnO4 used = Proportional Amount of H2O2 Used
(At 10 seconds)
3.0 mL – 2.5 mL = 0.5 mL of H2O2 used
The proportional amount of hydrogen peroxide used was then processed to create a line graph
showing the amount used at different time intervals. Also, the reaction rates for different time
intervals were calculated using the following formula:
Reaction Rate =
E2 - E1
t2 - t1
where
E1= initial amount of H2O2 decomposed
E2 = end amount of H2O2 decomposed
t1= initial time
t2 = end time
For example, for 0 sec – 10 sec or the initial reaction rate:
0.5 mL - 0.0 mL
10 sec - 0 sec
= 0.05 mL/ sec
III.
Processed Data Presentation
The Amount of H2O2 Used in Reaction at
Different Time Intervals
Amount of H202 Used (mL) (±mL)
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
Time (seconds) (±0.5 seconds)
Reaction Rates for Different Time Intervals
Time Interval (seconds) Reaction Rate (ml H202/sec)
Initial (0-10)
(10-30)
(30-60)
(60-120)
0.050
0.005
0.013
0.002
(120-180)
0.005
Conclusion and Evaluation
From this experiment, I was able to conclude that as the time interval increased, there
was increase in the decomposition of hydrogen peroxide. This is evident as at 10 seconds, the
amount of hydrogen peroxide used was 0.5 mL and finally, at 180 seconds, the amount used was
1.4 mL. However, the reaction rates for the time intervals showed that as the time intervals
increased, the rate at which the hydrogen peroxide decomposed decreased. This is seen as the
initial reaction rate (0 sec-10 sec) is the highest reaction rate at 0.05 mL/sec. This is also seen in
the graph as the line evens out as the time increases. Therefore, the rate decreases over time of
catalase activity. The reaction rate lowers to 0.017 mL/sec and finally to .005 mL/sec. This
decrease in rate can be explained by the enzyme activity as the time progresses. (Laboratory 2:
Enzyme Catalysis) At the beginning, when the hydrogen peroxide and catalase are mixed, the
substrate concentration is high and the molecules meet the active sites often. Many active sites
are available for binding, thus causing the reaction rate to be very high. However, as the time
interval increases, most of the enzymes or active sites are already in use which causes the
reaction rate to decrease. The enzyme becomes saturated with substrates, and therefore cannot
continue to increase its rate of catalysis. As less substrate molecules become available, the
reaction rate slows down until it eventually levels off or reaches zero. This is why the rate is
lowest between 60 and 180 seconds (LabBench). Because our findings can be explained by
scientific knowledge on enzyme behavior, catalyzed reactions, and reaction rates, our data is
valid and reliable.
My group did find weaknesses within this experiment. One significant weakness involved
the use of the syringe. The syringe kept drawing in too much air and this might have affected our
results when reading the initial and final values on the syringe. Also, because we only had one
trial, the validity of our data can be questioned. In addition, the sample that was titrated was very
small and therefore, only gave a slight difference between the reaction rates. Another weakness
could have been that since the cups were open and syringes had to be reused, the catalase or the
solution could have gotten contaminated or come into contact with another substance.
One way to improve our experiment would be to use a buret instead. This would ensure
that there would be no air bubbles. To increase validity of our results, we could do more trials
and also calculate mean and standard deviation for our results. To exaggerate the difference
between the reaction rates, a bigger sample size could be used for titration. Possibly, we could
titrate 25 mL- 50 mL of the catalyzed solution with potassium permanganate. To prevent the
solution from being possibly contaminated, we could use a different syringe for each titration.
Works Cited
"LabBench." Prentice Hall Bridge Page. Web. 30 Oct. 2011.
<http://www.phschool.com/science/biology_place/labbench/lab2/design.html>.
"Laboratory 2: Enzyme Catalysis." Advanced Placement Biology. Web. 30 Oct. 2011.
<http://www.jpsaos.com/jones/labs/AP_lab_2_enzyme_catalysis.pdf>.