Comparison of the Effects of Inorganic Catalysts and Enzymes on Peroxide Decomposition.

Introduction: (Initial Observation)

All catalysts can speed up a chemical reaction, however not all catalysts have the same effectiveness. Some catalysts increase the rate of reaction much more than others. That is why it is common for scientists to test multiple catalysts to see which ones yield a better results.

In some chemical reactions you have the choice of using organic catalysts or inorganic catalysts. That is where you compare samples of both groups.

In this project, you will compare different organic and inorganic catalysts for their effectiveness on decomposition of Hydrogen Peroxide.

Information Gathering:

Find out about catalysts and their mechanism on changing the rate of a chemical reaction. Read books, magazines or ask professionals who might know in order to learn about different organic and inorganic catalysts as well as chemical reactions that require catalysts. Keep track of where you got your information from.

Following are samples of information that you may find.

What is a Catalyst?

A Catalyst is a substance that can cause a change in the rate of a chemical reaction without itself being consumed in the reaction; the changing of the reaction rate by use of a catalyst is called catalysis. Substances that increase the rate of reaction are called positive catalysts or, simply, catalysts, while substances that decrease the rate of reaction are called negative catalysts or inhibitors.

Catalysts work by changing the activation energy for a reaction, i.e., the minimum energy needed for the reaction to occur. This is accomplished by providing a new mechanism or reaction path through which the reaction can proceed. When the new reaction path has a lower activation energy, the reaction rate is increased and the reaction is said to be catalyzed. If the activation energy for the new path is higher, the reaction rate is decreased and the reaction is said to be inhibited.

Natural Catalysts Enzymes are the commonest and most efficient of the catalysts found in nature. Most of the chemical reactions that occur in the human body and in other living things are high-energy reactions that would occur slowly, if at all, without the catalysis provided by enzymes.

What Catalysts can be used for Hydrogen Peroxide Decomposition?

It is interesting to note that a wide variety of substances catalyze the breakdown of hydrogen peroxide into water and oxygen gas,

H2O2 —> 1/2 O2(g) + H2O

Some of these substances include various metal salts and the Catalase enzyme which is widespread throughout the living kingdom. There is some logic to this in that hydrogen peroxides strong oxidizing nature tends to make it a toxic substance. Interestingly, the action of hydrogen peroxide on open cuts is due to the Catalase in our blood, not due to bacteria. The hydrogen peroxide acts as a disinfectant because bacteria lack the enzyme to render it harmless. Thus the bacteria are killed, while our Catalase protect us. Not every bacteria is killed in this fashion. Bacteria can be categorized as “Catalase positive” or “Catalase negative” using a procedure much like this lab. The body can also produce its own hydrogen peroxide which can be used to attach foreign cells at the molecular level. The hydrogen peroxide is particularly effective in reacting with the biomolecules with carbon-carbon double bonds.

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

The purpose of this project is to compare the effect of different organic and inorganic catalysts in decomposition of hydrogen peroxide. We need to know which catalysts are the most effective.

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

Independent variable (also known as manipulated variable) is the type of substance that we for catalytic ability in decomposition of hydrogen peroxide.

Dependent variable (also known as responding variable) is the rate of decomposition. We determine the rate of decomposition by the rate of oxygen production.

Controlled variables are all other environmental factors that may have a side effect on decomposition of hydrogen peroxide. These variables are temperature and light.

Constants are the concentration and the amount of hydrogen peroxide in each experiment, as well as method and procedures.

Hypothesis:

Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.

Following is a sample hypothesis for this project.

Manganese Dioxide is the most effective catalyst for decomposition of Hydrogen Peroxide.

My hypothesis is based on my common sense and the fact that Manganese Dioxide is well known as a catalyst.

Note that hypothesis does not have to be correct. You may have to reject your own hypothesis based on the results on your experiments.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Experiment 1:

This experiment compares inorganic catalysts and enzymes in terms of their effect on the decomposition of hydrogen peroxide.

Procedure:

• Place 5 ml of the hydrogen peroxide in each of the 7 test tubes
• Add the catalysts according to the chart below
• Observe the rate of oxygen production in each tube and use it to rank the catalysts
• Make comparisons between the organic enzymes as opposed to the inorganic catalysts in rate of production of gas.

You can visually determine the rate of oxygen production and rank the catalysts based on their effectiveness. However, If you really want to measure the amount of gas produced in each tube, you can use one of these two methods.

• Mount a balloon on the top of each test tube immediately after adding the catalyst. The rate of inflation of balloons is the rate of oxygen production. Record the size of balloon after a certain period of time such as 5 minutes or 60 minutes.
• The balloon that you use for this purpose must be soft and easy to blow. You may need to blow up the balloon with air and leave it overnight before doing your experiment. Then you can empty the air; suck the extra air out and connect it to the mouth of the test tube.
• You can connect a narrow glass or plastic tube to the mouth of the test tube. Produced oxygen will push back a small amount of water that is already in the tube. This water must be placed in the narrow tube before the experiment starts. To seal the narrow tube to the mouth of the test tube you may use chewed/ soft gum.

Experiment 2:

In this experiment you will test the effect of heat on organic and inorganic catalysts.

Procedure:

Repeat the procedure for part A, except boil the catalysts before adding it to the hydrogen peroxide. DO NOT HEAT THE HYDROGEN PEROXIDE.

To boil the catalysts, put the catalyst substances in each of the six test tubes and then place the test tubes in a boiling water bath for about 5 minutes. You can use a a 400 ml beaker half filled with hot/boiling water for the bath. Add the hydrogen peroxide after the substances have cooled. Record the reactions of the hot catalysts with new samples of each of the materials used in Part A.

Reactions with Hot Catalysts

DISPOSAL: Any solids can be disposed in the wastebasket. Liquids may be washed down the sink.

HAZARDS: Use caution with hydrogen peroxide. It can cause eye and skin irritations and is an oxidizer. Avoid contact with ferric chloride as it is a tissue irritant.

Materials and Equipment:

Materials Needed for this project may vary based on the catalysts that you choose to test. The following is a sample list of material.

1. 1000 ml of 6 % hydrogen peroxide (From pharmacy or supermarket)
2. Test tube rack (From MiniScience.com or other science suppliers)
3. 5 g of solid MnO2 (From MiniScience.com or ChemicalStore.com)
4. 5 g of solid FeCl3 (From electronic component stores, radioshack, or art stores)
5. 5 ml blood (from uncooked meat)
6. Paring knife
7. One each of banana, potato, pineapple and apple or any other fruit (From supermarkets or farmers markets)
8. 7 large test tubes (From MiniScience.com or other science suppliers)

MnO2 or Manganese Peroxide (Manganese Dioxide) is the black substance that you may carefully remove from a cheap alkaline battery. The battery can be new or old. Wear gloves and goggles if you want to try this. You may also buy this from chemical stores (or ChemicalStore.com).

FeCl3 or Ferric Chloride is an etching substance available from electronic component stores.

If you do not want to measure the amount of oxygen, you can substitute test tubes with petri-dishes, aluminum foils, or similar small plates.

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.

Calculations:

No calculation is required for this project.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.

Conclusion:

Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.

References:

Visit your local library and find books related to catalysts or general chemistry books that contain a chapter about catalysts. Such books can provide you with some valuable information about catalysts.

Following are some web resources.

http://www.bact.wisc.edu/microtextbook/Metabolism/Enzymes.html

http://lib.harvard.edu/e-resources/details/c/catareac.html

http://www.ecu.edu/si/cd/stella/enzstudent.pdf

Catalysis