Name: __________________________________________________________________________________ Date: ________
Kinetics - A Study of Chemical Reaction Rates with Enzymes
Period: ______
Integrated Science 4
BACKGROUND INFORMATION
Many of the chemical reactions that have been observed so far in Integrated Science have resulted in color
changes, formation of a precipitate, and evolution of a gas. Most of these have occurred almost immediately upon
mixing. The rate of these reactions appears to be controlled by diffusion. Many other reactions, however, occur at a
slower rate and the progress of the reactions can be followed over time. How fast a reaction occurs has application
not just in chemistry, but also in biology, geology, ecology, and engineering. Kinetics is the study of the rates of
chemical reactions. Kinetics is from the Greek word kinein meaning “set in motion, or move”. Scientists must be able
to measure and control reaction rates in order to make compounds both safely and economically. Controlling the
rates of reactions can also allow the time needed to understand how reactions occur at the molecular level. Being
able to study how a reaction occurs helps in understanding the pathway of the reaction.
Several factors can influence or control the rate of a reaction. These include concentration of the particles,
temperature, and surface area of the particles. For instance, if a piece of wood gets hot enough, it will burn. This
combustion process could take several hours. However, if the log were ground into a powder and then spread out, it
would create an explosion when lit. Still the same combustion reaction, but the rate of the reaction would be
changed. The reason for the change involves a difference in surface area of the particles. Powdered wood has more
surface area than a log, therefore, exposure to oxygen molecules in the air would be greater.
Previous lessons have indicated that a chemical reaction occurs when the chemical bonds between atoms are
broken, the atoms rearranged, and new substances formed. For this to happen, energy is required. The amount of
energy to start a reaction is called activation energy. Scientists have decided that reacting atoms or molecules must
collide with sufficient energy if they are to react. In the example above, lighting the log or powdered wood provided
the activation energy needed to get the reaction started. The energy for collisions could also come from the
temperature of the system as well as the concentration of colliding particles. This, however, does not alter the
activation energy needed. There are substances that can lower the energy needed to get start a reaction.
A catalyst is any substance that increases the rate of a chemical reaction by lowering the activation energy.
By doing this, the rate of the reaction is, therefore, increased (Nelson, 2000). Iron rusts faster, for example, in the
presence of sodium chloride; food molecules are more efficiently digested in the presence of vitamins; and gasoline
is more thoroughly combusted in the presence of platinum, the active component of most automotive catalytic
converters. In these examples, sodium chloride, vitamins, and platinum are catalysts. Rather than being consumed
during a chemical reaction, a catalyst can be regenerated or recycled to continue to form more product molecules
(Hewitt et.al., 1999). Biological catalysts, called enzymes, also alter the rate of reactions. Enzymes are protein
catalysts that speed up or slow down a biochemical reaction but are not consumed by the reaction (Childers, 1994).
The reactants of an enzyme-catalyzed reaction are known as substrates.
In this investigation, hydrogen peroxide (H2O2) will be decomposed into water and oxygen. This chemical
reaction occurs spontaneously, but the rate is very slow. Temperature, concentration, and surface area will be used
to study how the rate of this reaction can be altered. The source of the enzyme, catalase, will be potato .
2 H2O2 --------> 2 H2O + O2
Works Cited:
Childers, M. (May, 1994). Enzymes. Retrieved January 25, 2002 from
http://askeric.org/Virtual/Lessons/Science/Biology/BIO0024.html.
Hewitt, P., Suchocki, J., and Hewitt, L. A. (1999). Conceptual Physical Science. Menlo Park, California: Addison
Wesley Longman Inc.
Nelson, G. (2000). Catalase Lab. Retrieved on January 25, 2002, from:
http://www.accessexcellence.org/AE/ATG/data/released/0074-GenNelson/
PROBLEM STATEMENT:
Read the design and then use the EDR to write a problem statement on YOUR OWN
piece of paper.
HYPOTHESIS:
After reading the background Information AND readings given in class, use the EDR to hypothesize
the effects of surface area of potato, temperature of the reaction, and concentration of hydrogen peroxide on
enzymatic reactions. Use APA format to CITE YOUR SOURCES. Write this on YOUR OWN piece of paper.
DESIGN:
Materials
2- 1L plastic beakers
2 - 400 mL plastic beakers
2 - 100 mL graduated cylinders
2 - test tubes
test tube rack
thermometer
test tube brush
1 – scoopula
1 - forceps
mortar and pestle
metric ruler
wax pencil
2 - glass elbows with stoppers and hoses
1.5% hydrogen peroxide (H2O2) solution**
3% hydrogen peroxide (H2O2) solution**
Multiple pieces of fresh potato (1 g each)**
ice
**Materials that will be discarded in the waste jar (after each trial)
Safety:
Hydrogen peroxide is a reactive material. Avoid skin/eye contact. Should a splash or spill occur, call your teacher
immediately; flush the area with water for 15 minutes. Goggles should be worn during lab. Wash hands, glassware,
and lab table thoroughly following the experiment.
Procedure:
Part 1: Surface Area of Potato
1. Fill the plastic 1 L beaker half full with tap water.
2. Fill both 100 mL graduated cylinders completely with water and invert into the beaker of water. If any air bubbles
present, refill the cylinder(s) again.
3. Insert the end of a hose into each graduated cylinder.
4 Label two test tubes #1 and #2. With a marking pencil draw a line 2 cm from the bottom of each test tube.
5. Pour 3% H2O2 up to the mark in both test tubes.
6. Get two pieces of potato that weigh 1 gram each.
7. Cut one piece of potato into pieces with a scalpel (this will be the “chopped” potato ).
8. Use a scoopula to place the CHOPPED potato into test tube #1 while another member puts the sample of the
WHOLE potato into test tube #2. Stopper the test tubes IMMEDIATELY. NOTE: Be certain that the potato makes
contact with the H2O2. Gently swirling the test tube to ensure constant contact is a great way to keep the reaction
going.
9. Record any qualitative observations for the reactions in your data table.
10. After 2 minutes, record the volume of oxygen produced.
11. Pour the contents of test tubes into the waste jar. Wash the test tubes thoroughly with water and a brush.
12. Repeat steps 1-11 for a total of three (3) trials.
Part 2: Temperature of H2O2
1. Repeat steps 1-3 from Part 1.
2. Get two pieces of potato that weigh 1 gram each.
3. Fill one 400 mL plastic beaker half full of water and add ice to the water. Let it sit for 1 minute and record the
temperature of the ice water.
4. Fill the other 400 mL plastic beaker half full of warm TAP water. Let it sit for 1 minute and record the
temperature of the water.
5. Label the two test tubes C and W. If necessary, re-draw a line 2 cm from the bottom of each test tube.
6. Pour 3% H2O2 up to the mark in both test tubes.
7. Set one test tube in the beaker with ice and the other test tube in the beaker with warm water.
8. AT THE SAME TIME, add the 1 g pieces of WHOLE potato pieces to each test tube. Stopper both test tubes
IMMEDIATELY. NOTE: Be certain that the potato makes contact with the hydrogen peroxide (H2O2). Gently swirling
the test tube to ensure constant contact is a great way to keep the reaction going. Keep the test tubes in the hot
and cold water as you swirl.
9. Record any qualitative observations for the reaction in your data table.
10. After 2 minutes, record the volume of oxygen produced.
11. Pour contents of test tubes into the waste jar. Wash the test tubes thoroughly with water and a brush.
12. Repeat steps 1-11 for a total of three (3) trials.
Part 3: Concentration of Substrate (H2O2)
1.
2
3.
4.
5.
6.
Repeat steps 1 - 3 from Part 1.
Label two test tubes #1 and #2. If necessary, re-draw a line 2 cm from the bottom of each test tube.
In test tube #1, pour 3% H2O2 up to the mark.
In test tube #2, pour 1.5% H2O2 up to the mark.
Repeat steps 8 – 11 from Part 2.
Repeat steps 1 – 5 for a total of three (3) trials.
RESULTS:
Table 1. Effects of surface area of potato during enzymatic reactions
Test
tube
Substance Tested
Volume of oxygen
generation (mL)
Qualitative Observations
Trial 1
1
Ground Potato
and
3% H2O2
2
Whole potato and
3% H2O2
Trial 2
Trial 3
Table 2. Effects of temperature of potato during enzymatic reactions
Test
tube
Substance Tested
Temp
(C)
Volume of oxygen
generation (mL)
Trial
1
C
Trial
2
Qualitative Observations
Trial
3
Cool Potato and
3% H2O2
W
Warm potato and
3% H2O2
Table 3. Effects of concentration of hydrogen peroxide during enzymatic reactions
Test
tube
Substance Tested
Volume of oxygen
generation (mL)
Qualitative Observations
Trial 1
1
Trial 2
Trial 3
Whole Potato and
3% H2O2
2
Whole potato and
1.5% H2O2
DATA PROCESSING AND PRESENTATION:


Refer to the EDR!!
Calculations: Complete calculations to analyze the data for the tests conducted.
Graphs: For each test, make a bar graph of the average amount of oxygen generated by the reaction (you’ll
make 3 bar graphs)
CONCLUSION AND EVALUATION:
Use the EDR to write and TYPE a conclusion and evaluation.