Catalyst, a substance that alters the rate of a chemical reaction without itself undergoing any chemical change. Enzymes, which are among the most powerful catalysts, play an essential role in living organisms, where they accelerate reactions that otherwise would require temperatures that would destroy most of the organic matter.
A catalyst in a solution with, or in the same phase as, the reactants is called a homogeneous catalyst. The catalyst combines with one of the reactants to form an intermediate compound that reacts more readily with the other reactant. The catalyst, however, does not influence the equilibrium of the reaction, because the decomposition of the products into the reactants is speeded up to a similar degree. An example of homogeneous catalysis is the formation of sulphur trioxide by the reaction of sulphur dioxide with oxygen, in which nitric oxide serves as a catalyst. The reaction temporarily forms the intermediate compound nitrogen dioxide, which then reacts with oxygen to form sulphur oxide. The same amount of nitric oxide exists at the end as at the start of the reaction.
A catalyst that is in a separate phase from the reactants is said to be a heterogeneous, or contact, catalyst. Contact catalysts are materials with the capability of adsorbing molecules of gases or liquids on to their surfaces. An example of heterogeneous catalysis is the use of finely divided platinum to catalyze the reaction of carbon monoxide with oxygen to form carbon dioxide. This reaction is used in catalytic converters mounted in cars to eliminate carbon monoxide from the exhaust gases.
Some substances, called promoters, do not have catalytic ability by themselves but increase the effectiveness of a catalyst. Materials that reduce the effectiveness of a catalyst, on the other hand, are referred to as poisons. Lead compounds reduce the ability of platinum to act as a catalyst; therefore, a car equipped with a catalytic converter for emission control must be fuelled with unleaded petrol. Catalysts are of major importance in today's industrial world. One current area of active research in catalysis is that of e enzymes. Natural enzymes have long been used by a few industries, but fewer than 20 such enzymes are presently available in industrial amounts
Enzymes are classified into several broad categories, such as hydrolytic, oxidizing, and reducing, depending on the type of reaction they control. Hydrolytic enzymes accelerate reactions in which a substance is broken down into simpler compounds through reaction with water molecules. Oxidizing enzymes, known as oxidizes, accelerate oxidation reactions; reducing enzymes speed up reduction reactions, in which oxygen is removed. Many other enzymes catalyze other types of reactions.
LOCK AND KEY THEORY:
Enzymes are large proteins that speed up chemical reactions. In their globular structure, one or more polypeptide chains twist and fold, bringing together a small number of amino acids to form the active site, or the location on the enzyme where the substrate binds and the reaction takes place. Enzyme and substrate fail to bind if their shapes do not match exactly. This ensures that the enzyme does not participate in the wrong reaction. The enzyme itself is unaffected by the reaction. When the products have been released, the enzyme is ready to bind with a new substrate.
There are several factors that can effect the breakdown of the reaction them being; temperature, substrate concentration and the enzyme concentration.
You can measure the reaction by setting up your apparatus and every 10cm3 take a reading of time from your stop clock.
The temperature and the amount of substrate concentration will affect the production of gas.
This field studies the rates of chemical processes as a function of the concentration of the reacting species, of the products of the reaction, of catalysts and inhibitors, of various solvent media, of temperature, and of all other variables that can affect the reaction rate. It is an essential part of the study of chemical kinetics to seek to relate the precise fashion in which the reaction rate varies with time to the molecular nature of the rate-controlling molecular collision involved in generating the reaction products. Most reactions involve a series of step-by-step processes, the sum of which corresponds to the overall, observed reaction proportions (or stoichiometry) in which the reactants combine and the products form; only one of these steps, however, is generally the rate-determining step (RDS), the others being much faster. By determining the nature of the RDS from the mathematical analysis of the reaction kinetics and by investigating how the reaction conditions (for instance, solvent, other species, and temperature) affect this step, or cause some other process to become the RDS, the physical chemist can deduce the mechanism of a reaction.
The factor of collision theory can be related to my preliminary investigation because the time it takes for my reaction to finish will depend on how fast the reaction is going. If the reaction is heated then more collisions will take place between atoms meaning the reaction will be very quick. If the reaction however was to lose heat then the amount of collisions will be less meaning the rate would be slower.
PRELIMINARY INVESTIGATION:
WHY DO WE DO A PRELIMINARY?
We need to do a preliminary because it helps us to find out how it will work. It also helps us to set the constants. It helps us to prepare for the main investigation. In the preliminary we need to collect 5 sets of results with 5 different volumes of oxygen e.g. we will be reacting 5cm3 of 5% yeast with 5cm3 of 20 vol. H2O2.
From the preliminary we can also learn the basic factors that affect the breakdown of hydrogen peroxide with the enzyme catalyse.
TABLE OF PRELIMINARY RESULTS:
PRELIMINARY CONCLUSION:
We do a preliminary to inform the plan in our investigation. It helps us to find the concentrations to use and if there are any problems with the experiment, which can be improved for the main investigation. It also helps us to decide on the quantities to collect and measure. From my preliminary I found that I should use: 5cm3 of yeast solution and 5cm3 of 20vol. H202. I have also decided to collect 40cm3 of distilled water in order to allow for the factor of displacement.
PRELIMINARY INVESTIGATION APPARATUS:
FAIR TEST:
In this experiment I will need to make it a fair test so that my results are fair. Factors that can affect the test not being fair are:
- Too much hydrogen peroxide in one of the tests
- Too much yeast solution in the conical flask
- Not enough water in the burette
- Make sure that I clean the apparatus properly when I change the amount of yeast solution and hydrogen peroxide.
If I were to make the test unfair the results that I took would all be wrong meaning that my experiment would be wrong and I would have to write it again.
MAIN INVESTIGATION:
I began my investigation by setting up the equipment I was going to use in my investigation. I then took a note of the constants I said I was going to use in my main investigation from my preliminary so as I knew what dilutions I needed.
After the beginning points in my investigation I had to start the main experiment. I started with 5% yeast solution in the conical flask and 5cm3 20vol. H202 in the syringe. I began the experiment from 40cm3 because I wanted to allow for the factor of displacement from 50cm3 to 40cm3. Every 10cm3 of the solution in the burette that was lost I took a reading from the stop clock i.e. from 40cm3 to 30cm3 etc. I carried out this test 3 times so that I could find an average time. After the experiment I cleaned all of the equipment in order to make sure that there were no particles left over from the previous experiment, in order to keep it a fair test.
I then reduced the yeast content to 4% and kept the concentration of H202 the same (the concentration of H2O2 will be the same throughout the entire investigation.) and carried out the same test I had done in the previous experiment.
In the next experiment I reduced the concentration of yeast to 3% and followed the same guidelines as I had done in the previous experiments.
In the next experiment I reduced the concentration of yeast to 2% and followed the same guidelines as I had done in the previous experiments.
In the next experiment I reduced the concentration of yeast to 1% and followed the same guidelines as I had done in the previous experiments.
After I had completely finished taking results I put my average results into a table. I will also find an average time as well as an average rate. I will work out the average rate by using the equation rate = volume of O2/ time taken.
RESULTS:
ANALYSING MY RESULTS:
After observing my results I can see that as I reduced the amount of yeast in the conical flask the average time became slower meaning the average rate was very slow. I also found that when I reduced the amount hydrogen peroxide in the syringe but increased the amount of yeast back up to 5cm3 of 5% yeast the average time was a lot slower and the average rate was very slow too.
In conclusion of my investigation I have found that the more hydrogen peroxide there is, the more yeast solution you would need. That is why I feel it went quicker when there was a large amount of yeast mixed with a large amount of hydrogen peroxide. But when there is less yeast but the same amount of hydrogen peroxide the breakdown of the H2O2 becomes a lot slower. I can also see that when the amount of hydrogen peroxide is reduced but the amount of yeast increased the reaction is a lot slower and is even more slower when the amount of yeast is reduced in the conical flask to 3cm3 of 5% yeast and the amount of hydrogen peroxide is kept the same in the syringe at 5cm3 of 10 vol. H2O2.
EVALUATION:
A good evaluation for my investigation would be that at first I didn’t think it went particularly well. This is because I struggled to get the apparatus together quickly as I was on my own doing the experiment. This meant that I lost time whilst doing the experiment meaning some of my results were rather rushed because I had to try and get all of the readings I needed in the time limit we had. Although I could have made up for this by going in at different times and doing my experiment again in my own time.
I think my method was good in its own way but could have been improved if I had spent more time on it and the apparatus I used would probably have been put together better had I spent more time on it which I should have done. The fact that I rushed the experiment could play a part on whether or not the experiment was a fair test. I say this because I may not have cleaned the apparatus properly when I was rushing to do the next test or I may have accidentally put to much yeast in the conical flask.
If I was to do the experiment again I would improve it by setting myself enough time to get the experiment done, this would mean that the tests would be fair and the results would be ‘true’. I would make sure that I set up the apparatus in a better way and if needed get the teacher to check it for me so that I know I am doing the experiment correctly. Also I would make sure that I concentrate in order to get the specified amounts of H2O2 in the syringe and yeast in the conical flask measured correctly so that the test is fair.
To conclude my investigation I feel my experiment went ok except for the errors that could have been avoided if I had put more time into my main experiment. These are factors that I can look at next time in order to improve my investigation.
BY MICHAEL BROWN YEAR 11/ SET 5
