Introduction: (Initial Observation)
Many chemical reactions don’t happen unless in presence of a third substance called catalyst. Although the catalyst does not enter the reaction and does not change itself, it has a key effect in start and continuation of the actual chemical process. In this project we will research to find out how catalysts work and why?
We will also research on industrial applications of catalysts and possible problems associated with them.
In the picture on the right A gentle flow of hydrogen gas is passed through a tube and over a wad of platinized asbestos. The gas ignites with a pop and continues to burn. The ignition may be repeated several times.
Information Gathering:
Find out about catalysts. Read books, magazines or ask professionals who might know in order to learn about the catalysts, how they work and their industrial applications. Keep track of where you got your information from. Following are some of the information that you might find.
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.
Mechanism of Catalysis
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. Inhibitors can provide an interesting challenge to the chemist. For example, because oxygen is an inhibitor of free-radical reactions, many of which are important in the synthesis of polymers, such reactions must be performed in an oxygen-free environment, e.g., under a blanket of nitrogen gas.
In some reactions one of the reaction products is a catalyst for the reaction; this phenomenon is called self-catalysis or autocatalysis. An example is the reaction of permanganate ion with oxalic acid to form carbon dioxide and manganous ion, in which the manganous ion acts as an autocatalyst. Such reactions are potentially dangerous, since the reaction rate may increase to the point of explosion.
Some substances that are not themselves catalysts increase the activity of a catalyst when added with it to some reaction; such substances are called promoters. Alumina is a promoter for iron when it is used to catalyze the reaction of hydrogen and nitrogen to form ammonia. Substances that react with catalysts to reduce or eliminate their effect are called poisons.
Types and Importance of CatalystsEnzymes: 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. For example, in the absence of catalysis, it takes several weeks for starch to hydrolyze to glucose; a trace of the enzyme ptyalin, found in human saliva, accelerates the reaction so that starches can be digested. Some enzymes increase reaction rates by a factor of one billion or more.
Enzymes are generally specific catalysts; that is, they catalyze only one reaction of one particular reactant (called its substrate). Usually the enzyme and its substrate have complementary structures and can bond together to form a complex that is more reactive due to the presence of functional groups in the enzyme, which stabilize the transition state of the reaction or lower the activation energy. The toxicity of certain substances (e.g., carbon monoxide and the nerve gases) is due to their inhibition of life-sustaining catalytic reactions in the body.
Laboratory and Industrial Catalysts
Catalysis is also important in chemical laboratories and in industry. Some reactions occur faster in the presence of a small amount of an acid or base and are said to be acid catalyzed or base catalyzed. For example, the hydrolysis of esters is catalyzed by the presence of a small amount of base. In this reaction, it is the hydroxide ion, OH−, that reacts with the ester, and the concentration of the hydroxide ion is greatly increased over that of pure water by the presence of the base. Although some of the hydroxide ions provided by the base are used up in the first part of the reaction, they are regenerated in a later step from water molecules; the net amount of hydroxide ion present is the same at the beginning and end of the reaction, so the base is thought of as a catalyst and not as a reactant.
Finely divided metals are often used as catalysts; they adsorb the reactants onto their surfaces (see adsorption), where the reaction can occur more readily. For example, hydrogen and oxygen gases can be mixed without reacting to form water, but if a small amount of powdered platinum is added to the gas mixture, the gases react rapidly. Hydrogenation reactions, e.g., the formation of hard cooking fats from vegetable oils, are catalyzed by finely divided metals or metal oxides. The commercial preparation of sulfuric acid and nitric acid also depends on such surface catalysis. Other commonly used surface catalysts, in addition to platinum, are copper, iron, nickel, palladium, rhodium, ruthenium, silica gel (silicon dioxide), and vanadium oxide.
Catalyst problems:
When catalyst is used in a reaction, you may want to deactivate the catalyst in order to control the rate of reaction or to stop the reaction. deactivating the catalysts is often a challenge for chemical industry.
Also catalysts used in many chemical reactions, later need to be removed. That is another problem that requires additional process.
For Industrial applications of catalysts visit the following links:
http://www.synetix.com/oleochemicals/applications.htm
Question/ Purpose:
The purpose of this project is to investigate catalysts and find out how they work and why? We will also study commercial applicants and problems with catalysts.
Identify Variables:
Variables that may affect the functionality of substance as a catalyst are the type of reaction and the type of chemicals involved in that reaction. In other words if platinum is a well known catalyst for many important reactions, it will not act as a catalyst for all reactions.
Hypothesis:
My hypothesis is that catalysts will modify the strength of bonds between different atoms in a molecule. Catalysts will do it using their own existing bonds or their potential energy.
Since different chemicals have different chemical bonds and different chemical reactions require different levels of reaction energy, catalysts have a very limited range of activity and there is no general purpose catalyst.
Experiment Design:
In our first experiment we test the most popular and well known catalyst, water. Water is a catalyst in oxidation of iron (rusting) and many other metals.
Experiment 1:
Get two large identical nails. Select a regular iron nail, not galvanized or coated type. Wash with soap, clean and dry both nails. place them somewhere exposed to the air. Spray one of them with water every day. After a few days compare the nails. Which one has more rust?
In this experiment that can be designed in many different ways, water is a catalyst for iron to react with oxygen in the air.
Experiment 2:
The objective of this experiment is to see how does the copper catalyst work on the reaction between zinc metal and dilute sulfuric acid.
The reaction between reactive metals, such as zinc, and dilute acids, is well-known. The rate of such a reaction can be assessed by the rate at which bubbles of hydrogen gas are produced.
Zn(s) + 2H1+ (aq) ———-> Zn2+ (aq) + H2 (g)
The choice of acids may also affect the rate of the reaction. In this investigation, it is recommended that 1.0 M sulfuric acid (not hydrochloric acid) be used.
Preliminary investigation.
If two small, equal pieces of granulated zinc are placed into small tubes and covered with 1 to 2 mL of dilute (1.0 M) sulfuric acid, bubbles should be seen, although they may not come quickly, especially at first when the acid is added to the zinc. As soon as a fine stream of bubbles is visible in both tubes, add to one of them either some small pieces of copper metal, or about 1.0mL of 0.5 M copper (II) sulfate solution. Does the addition of the copper make any difference to the rate at which bubbles are produced?
If copper (II) sulfate solution is used, it should be noted that the blue color disappears fairly quickly, and the zinc darkens in color. This is due to a displacement reaction, in which copper metal is precipitated onto the zinc: Zn(s) + Cu2+ (aq)———–> Zn2+ (aq) + Cu(s)
If there is indeed a difference in the rate at which bubbles are produced, then it may be possible to explain how the copper catalyst works.
Predicting a possibility.
If bubbles are produced faster from zinc and dilute sulfuric acid in the presence of copper metal, then it must be the copper metal that makes the difference. If another two small equal pieces of zinc are placed in fresh 1.0 M sulfuric acid, with one having a large enough strand of copper wire twisted around it, it may just be possible to see a difference in the way that hydrogen is produce. Zinc and copper together in an electrolyte (sulfuric acid) make an electrolytic cell. Zinc, the more reactive metal, is the anode, copper is the cathode, so hydrogen ions are likely to be reduced to hydrogen gas at the copper electrode.
Without the copper, there is no obvious electrolytic cell, so hydrogen gas would have to be produced by the direct reaction between zinc atoms and hydrogen ions at the surface of the metal.
Testing the possibility
Test the predictions made. It should be possible to see that with zinc and sulfuric acid alone, bubbles come from the surface of the zinc, but when copper wire is twisted around the zinc, (with a loose end of wire hanging free), hydrogen gas appears at the copper wire.
Additional notes:
- This experiment is effective with quite small quantities of materials. In the second (testing prediction) stage, the pieces of zinc with and without copper may be placed side by side in the same acid sample in a small flat dish.
- More advanced students may wish to test the zinc and copper wire with probes of a voltmeter to show that an electrolytic cell has indeed been created.
- Some students might consider whether the bubbles are originating from a reaction involving copper. A piece of the same copper wire, placed near the zinc pieces without touching them, might serve as a useful control. Text books say that no hydrogen is produced from copper and dilute sulfuric acid. Is there any blueness forming near the copper?
Experiment 3:
The purpose of this experiment is to see the effect of “manganese dioxide” catalyst on the rate of a reaction.
Chemicals
- 6% hydrogen peroxide solution (available at pharmacies)
- liquid dishwashing detergent
- manganese dioxide (is a black amorphous powder, used as glaze for ceramic and also used in some energizer batteries)
Equipment
- 250-mL beaker
- chemical scoop or spoon
- stirring rod or wooden splint
Caution should be used in handling hydrogen peroxide solution and in recovering manganese dioxide from a battery; both are caustic. Wear gloves. Carry out the reaction on a tray to contain any overflow. Wear goggles throughout preparation and experiment.
MODIFICATIONS/SUBSTITUTIONS
- 6% hydrogen peroxide solution is available from a drugstore or beauty supply store as Clairoxide.
- Manganese dioxide may be obtained from a battery. Use the solid substance between the electrodes.
- Clear plastic cups may be substituted for the beakers.
PROCEDURE
- Add 100 mL of the hydrogen peroxide solution to each beaker.
- Add a large squirt of liquid detergent to each beaker. Mix and observe; note the absence, or near absence, of bubbles being formed.
- Add about 1/8 to 1/4 tsp. of manganese dioxide to one beaker. Compare to the behavior of the mixture without the manganese dioxide.
DISPOSAL
Flush down the drain using lots of water.
DISCUSSION
A catalyst is a substance that is added to a reaction to increase the reaction rate. The catalyst allows the reaction to proceed by an alternate reaction mechanism with a lower activation energy. A catalyst is not consumed in a chemical reaction.
The reaction for the decomposition of hydrogen peroxide is:
2 H2O2(aq) —> 2 H2O(l) + O2(g)
This reaction normally proceeds very slowly. When the catalyst, manganese dioxide, is added, the rate of the reaction increases appreciably; this can be seen by the large volume of foam that is generated as the oxygen gas bubbles through the detergent solution. Little, if any, foam forms without the catalyst. The foam is gray in color because of entrapped, black manganese dioxide.
Materials and Equipment:
Can be extracted from the experiment section.
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 done in 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:
List of References
http://www.cobalt.chem.ucalgary.ca/group/met_intro.html
http://www.madsci.org/posts/archives/may98/895006914.Ch.r.html
