effect of hydrogen peroxide concentration on the rate of reaction
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IB Chemistry HL
Name: Yoojin Lee
Candidate Number: 002213-067
1
Candidate Name :Yoojin Lee
Candidate Number :002213-067
Date of Practical :August 23, 2010
Internal Assessment – Rate of Reaction
Research Question
How will changing hydrogen peroxide (H2O2) concentration affect the rate of reaction,
represented by the increase in pressure over time, measured using gas pressure sensor?
Introduction
Hydrogen peroxide (H2O2)1 is a by-product of biochemical metabolism. An accumulation of
hydrogen peroxide can be deadly, so it has to be decomposed. One of the decomposing
factors is an enzyme called Catalase. Catalase breaks hydrogen peroxide into water and
oxygen.
The chemical formula for the reaction is,
Since this is a decomposition reaction, it is exothermic. Although hydrogen peroxide can
gradually degenerate itself, it decomposes much faster with the help of Catalase, because
Catalase lowers the activation energy, the minimum energy barrier that hydrogen peroxide
molecules have to overcome to decompose.2
1 “Hydrogen,” Wikipedia, the free encyclopedia, http://en.wikipedia.org/wiki/Hydrogen_peroxide (accessed
October 22, 2010). 2 “The Hydrogen Peroxide Breakdown Examining Factors That Affect the Reaction Rate of Enzymes,” Alief
Independent School Districts
Vanguard,http://www4.alief.isd.tenet.edu/cahowe/biology/pak%202/The%20Hydrogen%20Peroxide%20Breakd
own.htm(accessed October 22, 2010).
IB Chemistry HL
Name: Yoojin Lee
Candidate Number: 002213-067
2
Figure 1 shows the reaction trend when enzyme is present.
3
Since the enzyme lowers the activation energy, the rate of reaction increases without
consuming enzyme. In this experiment, the substrate is hydrogen peroxide. The purpose of
this investigation is to find out the relationship between the substrate concentration and the
rate of reaction, which is measured by the change of pressure overtime, measured using gas
pressure sensor.
The gas pressure sensor is used because the reaction produces oxygen gas. The faster the
reaction is, the faster the pressure will increase. Thus, by examining the change of pressure
overtime, the rate will be calculated and analyzed. For this investigation, the initial rate of the
reaction is examined.
3 Ibid
IB Chemistry HL
Name: Yoojin Lee
Candidate Number: 002213-067
3
Hypothesis
When the amount of enzyme stays constant, the substrate concentration will determine the
rate of reaction. However, when the number of substrate molecules exceeds the available
number of enzyme, the rate of reaction will no longer increase, but stay constant. Since the
gas pressure sensor can take up to 180 atm, it is very difficult to calculate the initial rate of a
highly concentrated solution. Thus, this experiment will only consider low concentrations.
The rate of reaction will increase as the hydrogen peroxide concentration increases. However,
from a certain concentration, the rate will stay the same, even if the concentration increases,
because the amount of enzyme used is fixed.
Figure 2 shows the relationship between the rate of reaction and the hydrogen peroxide
concentration.
IB Chemistry HL
Name: Yoojin Lee
Candidate Number: 002213-067
4
Variables Variables Description Method of Measuring
Independent Hydrogen Peroxide
(Substrate) Concentration,
c/%
Hydrogen peroxide solution was diluted
to 50% using distilled water. Then the
diluted hydrogen peroxide was further
diluted to prepare 20%, 40%, 60%, 80%,
and 100%. Distilled water was used for
control (0% ethanol).
Triplicate trials were performed on each
concentration to obtain the mean.
Dependant Rate of Reaction of hydrogen
peroxide decomposition
Rate of reaction is represented by the
change of pressure over time. Pressure
was measured by using the gas pressure
sensor. The same sensor was used
throughout the experiment. Also the
shortest tube was used to reduce
systematic errors.
Controlled Recording initial rate As soon as the hydrogen peroxide is put
inside the test tube, it is immediately
capped with the gas pressure sensor to
record data.
Amount of enzyme The amount of enzyme is set to 10 micro-
liters. Micropipette was used for accurate
measurement, because an extra drop of
enzyme can alter the rate of reaction
significantly.
Temperature Since temperature is directly related to
the rate of reaction, the entire experiment
was conducted in the lab at a constant
room temperature, which is
approximately 25℃.
Volume of hydrogen peroxide
solution
Even though the solutions differ in
concentration, the volume for all of the
solutions stayed the same, which is 1.5
cm3 for all trials.
For accurate measurement, micropipette
was used throughout.
Size and type of test tubes The size and type of test tubes were
constant, because they can alter the
pressure. The same size and type of test
tubes were used throughout.
Hydrogen peroxide A new hydrogen peroxide was used
because hydrogen peroxide can
degenerate naturally. All of the trials used
hydrogen peroxide from the same
container.
Table 1 shows the independent, dependent, and controlled variables and the methods of
measuring
IB Chemistry HL
Name: Yoojin Lee
Candidate Number: 002213-067
5
Procedure
1. Serial dilution was performed following the diagram below.
Figure 3 shows the diagram for serial dilution method
2. 10µl of Catalase is added to the testing tube and the pressure build up was measured
instantly using the gas pressure sensor.
- While collecting data magnetic stirrer was used to release oxygen gas trapped
inside the solution with constant stirring.
- Top part of the test tube was manually held to minimize the temperature rise.
3. Steps 1 and 2 were repeated and performed with different concentrations to obtain
valid triplicate trials for each concentration.
Apparatus Materials Gas pressure sensor
Micropipette (± 0.006cm3)
Magnetic Stirrer
25cm3 Pipette (± 0.03cm
3)
Test tubes
Beaker
Hydrogen peroxide Catalase Distilled water
IB Chemistry HL
Name: Yoojin Lee
Candidate Number: 002213-067
6
Data Collection – Qualitative Data
The reaction started as soon as Catalase touched the surface of hydrogen peroxide. More
concentrated hydrogen peroxide produced more oxygen bubbles and the reaction rate was
faster, because it produced oxygen gas rapidly. On the other hand, more diluted hydrogen
peroxide reacted slowly and the oxygen bubbles were released sporadically.
Data Collection – Quantitative Data
Time,
t/ sec
Pressures of Different Hydrogen Peroxide Concentrations/ kPa
1.5 0.75 0.375 0.1875 0.09875
1st 2nd 3rd 1st 2nd 3rd 1st 2nd 3rd 1st 2nd 3rd 1st 2nd 3rd
0.00 100 100 103 100 100 103 100 103 103 100 100 103 100 100 103
60.0 100 100 103 100 100 103 100 103 103 100 100 103 100 100 103
120 105 100 100 104 100 103 100 103 103 100 102 103 100 100 103
180 114 107 100 106 103 105 102 105 105 102 103 104 100 103 104
240 119 117 107 108 105 108 105 108 107 104 104 105 100 103 105
300 124 123 116 110 108 113 108 110 109 105 105 106 100 104 106
360 127 129 125 112 110 117 110 113 111 106 106 106 100 104 106
420 130 134 132 114 112 120 112 115 112 107 106 108 103 105 108
480 134 138 136 115 114 123 114 116 113 107 107 105 103 105 107
540 137 141 140 117 115 125 115 117 114 108 107 106 103 105 108
Table 2 shows condensed raw data for the experiment extracted from Logger Pro.
IB Chemistry HL
Name: Yoojin Lee
Candidate Number: 002213-067
7
Graph 1 shows the raw data for pressure build up of different hydrogen peroxide concentrations over time
IB Chemistry HL
Name: Yoojin Lee
Candidate Number: 002213-067
8
Data Processing
The gradient of a graph represents the change in pressure over time. Thus, it represents the
rate of reaction.
Table 3 shows the rates of pressure increase for different hydrogen peroxide concentrations (a)
Mean: average of triplicate trials for each set. (b)
SD: standard deviation for triplicate trials.
Sample Calculations
Rate of reaction =
Calculation of the mean rate of 1.5% hydrogen peroxide from the triplicate trials.
Mean ( ) =
=
0.113 kPa s
-1
Calculation of the standard deviation of 1.5% hydrogen peroxide from the triplicate trials.
Standard deviation =
=
= 0.015 kPa s-1
Hydrogen Peroxide
Concentration, c/%
Rate of Reaction, r/ kPa s-1
Trials
Mean(a)
Mean ± SD(b)
1 3 3
1.50000 0.130 0.110 0.0994 0.113 0.015
0.75000 0.0527 0.0417 0.0437 0.0460 0.0059
0.37500 0.0389 0.0299 0.0306 0.0331 0.0050
0.18750 0.0174 0.0251 0.0128 0.0184 0.0062
0.09875 0.0156 0.0251 0.0150 0.0186 0.0057
IB Chemistry HL
Name: Yoojin Lee
Candidate Number: 002213-067
9
Graph 2 shows the processed data of average rate of pressure increase over the hydrogen peroxide concentration
(a) Vertical error bar shows the standard deviation of the triplicate trials for the rate of reaction
(b) Horizontal error bar shows the uncertainty in H2O2 concentration.
y = 0.0678x + 0.0063
R² = 0.9695
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
-0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8
Avera
ge R
ate
of
React
ion, a/
kPa/s
ec
Concentration of Hydrogen Peroxide, c/%
Average Rate of Pressure Increase of
Different Hydrogen Peroxide Concentration
(a)
(b)
IB Chemistry HL
Name: Yoojin Lee
Candidate Number: 002213-067
10
Uncertainties
Concentration of
H2O2, c/%
% uncertainty for volume use
Total %
uncertainty/ %
Concentration
with uncertainty
Volume of H2O2
using
Micropipette
(ΔV = ± 0.006)
cm3
% uncertainty in
volume/ %
Volume of water
using
Micropipette
(ΔV = ± 0.006)
cm3
% uncertainty in
volume/ %
3.00000 0 0 0 0 0 0
1.50000 1.5 ± 0.012 (0.012/1.5)x100
= 0.8 1.5 ± 0.012
(0.012/1.5)x100
= 0.8 0.8+0.8 = 1.6 1.5±1.6%
0.75000 1.5 ± 0.012 (0.012/1.5)x100
= 0.8 1.5 ± 0.012
(0.012/1.5)x100
= 0.8
0.8+0.8+1.6
= 3.2 0.75±3.2%
0.37500 1.5 ± 0.012 (0.012/1.5)x100
= 0.8 1.5 ± 0.012
(0.012/1.5)x100
= 0.8
0.8+0.8+3.2
= 4.8 0.375±4.8%
0.18750 1.5 ± 0.012 (0.012/1.5)x100
= 0.8 1.5 ± 0.012
(0.012/1.5)x100
= 0.8
0.8+0.8+4.8
= 6.4 0.1875±6.4%
0.09875 1.5 ± 0.012 (0.012/1.5)x100
= 0.8 1.5 ± 0.012
(0.012/1.5)x100
= 0.8
0.8+0.8+6.4
= 8.0 0.09875±8.0%
Table 4 shows the percent uncertainty for volume use
Concentration of H2O2, c/% % uncertainty in concentration,
Δc/%
Absolute % uncertainty in
concentration,
Δc/%
Concentration, c/%
3.00000 0.0 0.0 3.00000±0.00000
1.50000 1.6 (1.6/100)x1.50000 = 0.02400 1.50000±0.02400
0.75000 3.2 (3.2/100)x0.75000 = 0.02400 0.75000±0.02400
0.37500 4.8 (4.8/100)x0.37500 = 0.01800 0.37500±0.01800
0.18750 6.4 (6.4/100)x0.18750 = 0.01200 0.18750±0.01200
0.09875 8.0 (8.0/100)x0.09875 = 0.00790 0.09875±0.00790
Table 5 shows the absolute uncertainties
IB Chemistry HL
Name: Yoojin Lee
Candidate Number: 002213-067
11
Conclusion
The data suggests that as the hydrogen peroxide concentration increases, the rate of diffusion
increases and that my hypothesis is valid. The linear regression and the high R2 value show
that there is a positive correlation between the rate of reaction and the hydrogen peroxide
concentration. However, it cannot be proved that the correlation is always directly
proportional. When observing the first two data on 0.09875% and 0.1875%, there is no
obvious increase and rather seems overlapping. Perhaps, this might be due to the fact that the
hydrogen peroxide concentration was too low. On the other hand, 1.5% has a huge error bar,
representing that the triplicate data were not consistent. Thus, it will not be taken into account
for examining the trend for this investigation. Otherwise, the graph seems to be smoothly
increasing. All data except 0.09875% show a legitimate positive correlation, because the
vertical error bars to not overlap at all. The results tell that when the hydrogen peroxide
concentration is high, the reaction rate increases. Thus, the results lead to the conclusion that
the rate of reaction is directly proportional when the hydrogen peroxide concentration is
greater than 0.09875%.
Evaluation
Although the trials for 1.5% had a wide range, the experiment is justifiable because reliable
triplicate trials were obtained. This is also reflected by the small vertical deviation on the
Graph 2. The uncertainty of the hydrogen peroxide, shown by the horizontal error bar, varies
with the concentration; higher concentrations have wider uncertainty than lower
concentrations. Although it seems likely that there is a positive correlation according to the
Graph 2, the linear regression does not pass through the origin of the graph, because based on
the linear regression equation, the y-intercept is 0.00063%. This shows that both systematic
and random errors were present.
IB Chemistry HL
Name: Yoojin Lee
Candidate Number: 002213-067
12
Since this experiment dealt with small amount of Catalase as well as the substrate hydrogen
peroxide, small systematic errors led to large uncertainties. For instance, in preparing
different concentrations of hydrogen peroxide, one extra drop of a solution could have altered
the concentration to a great extent. Major errors could have been reduced if the experiment
was conducted under larger system.
Limitations and Improvements
Limitations Improvements
Since the amount of Catalase was limited and
small in quantity, only 10µl of Catalase was
used for each trial to ensure enough is left for
multiple trials. Although a micropipette was
used, there was small amount of the enzyme
solution left on the wall of the tip after
releasing. Because only small amount of
Catalase was used, this could have resulted in
huge uncertainties in measuring the rate.
Additionally, the entire substrate amount was
reduced to 1.5ml. Thus, small errors yielded
huge uncertainties.
The whole system needs to be enlarged to
reduce uncertainties. Thus, a greater amount
of Catalase and hydrogen peroxide is needed.
In larger scale experiments, small errors will
be negligible and the results will be more
reliable and justifiable.
Since the test tube had to be manually capped
with the gas pressure sensor, it inevitably
included human error because of human
reaction time. Thus, the initial rate might not
be accurate.
To reduce human errors, more advanced
apparatus has to be used. To obtain accurate
data, the pressure has to be measured as soon
as Catalase hits the surface of hydrogen
peroxide, because the reaction starts
instantaneously, even if the concentration is
low.
The solutions were prepared by performing
only serial dilutions due to time constraints
and limited amount of Catalse. Since the
different concentrations were obtained by
performing serial dilution, the concentration
decreased by half, lacking variety in
concentrations. The results would have been
better if more solutions of different
concentrations between 0.4% and 1.5% were
tested.
To prepare more solutions of different
concentration, more amount of hydrogen
peroxide has to be used and enough Catalase
must be present. A variety of solutions could
be prepared by altering the percentages
manually and not perform serial dilutions.
Table 5 shows the limitations and the improvements
IB Chemistry HL
Name: Yoojin Lee
Candidate Number: 002213-067
13
Bibliography 1 “Hydrogen.” Wikipedia, the freeencyclopedia.
http://en.wikipedia.org/wiki/Hydrogen_peroxide(accessed October 22, 2010).
2 “The Hydrogen Peroxide Breakdown Examining Factors That Affect the Reaction Rate of
Enzymes.” Alief Independent School Districts
Vanguard.http://www4.alief.isd.tenet.edu/cahowe/biology/pak%202/The%20Hydrogen%20
Peroxide%20Breakdown.htm(accessed October 22, 2010).
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