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

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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

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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

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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

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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).