Results for pre-test:
Conclusion:
The results show that PH 9 was the optimum ph for the enzyme activity but after looking at a variety of sources such as The Biological science book 1 and 2 by green, stout and Taylor and our science teacher Mrs Howard we decided to use the ph 8 as we found out that the optimum PH level for this reaction was ph 7.6. After the pre-test results we decided to use a higher concentration of hydrogen peroxide going from a concentration volume of 10 to a concentration level of 20 this was because the results that we got didn’t start reacting quickly enough after we put all of the substances together in the conical flask. So that we could get a faster and more varied set of results. We therefore reduced the amount of liver we used so that the reaction wouldn’t take place too quickly giving bogus harder to track results and stop the reaction becoming too vigorous and bubbling up into the delivery tube.
Main test:
Aim: To investigate the effect of changing substrate concentration on catalase reaction rate
Hypothesis: The best concentration should be 100% as there will be more of the hydrogen peroxide to react with the catalase molecules.
Equipment:
- Gas syringe- to measure the oxygen to the nearest cm³ (dependent variable) the oxygen produced was the outcome that we decided to look at to see what was the best concentration this changed for every different concentration.
- Delivery tube- to let the oxygen pass through into the gas syringe
- Conical flask- to hold the substances
- Hydrogen peroxide(20 volume)-to react with the catalyse (controlled variable) we measured out the same volume of hydrogen peroxide only changing the amount mixed with the water leading to a fair test with reliable results.
- Balance- to weigh the liver to the nearest hundredth of a gram
- Weighing boat- to hold the liver on the balance
- Liver- source of catalase (controlled variable) we weighed this out trying to get as close to 1 gram as possible to the nearest hundredth of a gram we gave an error bar of 0.03 of a gram different either way this resulted in a very accurate and controlled test and results.
- White tile- to cut the liver on
- Scalpel- to cut the liver with
- Stop clock- to time the reaction
- Clamp- to hold the gas syringe
- Goggles- to protect your eyes
- PH buffer, 4, 5, 6, 7, 8, 9- to see which works best in the reaction (independent variable) we changed these by testing different pH levels but kept the volume of it the same keeping a fair reliable test and accurate results.
- 2 Measuring cylinders- to measure the substances accurately to the nearest cm³
- Retort stand- to clamp the clamps to the gas syringe
Method:
- Collect all equipment
- Clamp the clamp to the retort stand to clamp the gas syringe
- Attach the delivery tube to the gas syringe
- Measure out 20cm³ of hydrogen peroxide and distilled water solution in the measuring cylinder.
- Measure out 5cm³ of PH buffer 8 (as it worked the best in the pre-test)
- Mix in the conical flask with the hydrogen peroxide
- Cut and measure out 1 gram of liver
- Tip the liver into the conical flask
- Quickly start the stop clock timer and as possible after mixing them all together put the delivery tube cork in the top of the conical flask
- Wait 90 seconds to let the reaction start
- Restart the stop clock and record the oxygen produced every 30 seconds for 4 minutes
- If the gas syringe reaches 100cm³ quickly remove the syringe from the conical flask, then push the syringe back to 0cm³, then replace the gas syringe, connecting it back with the conical flask.
- Repeat twice with the same concentration
- Repeat trice with all of the other different concentrations except 0% as it will not react (being made up of just water).
- Clean your desk and put all of your equipment away and wash your hands.
How we controlled our variables: As we tested all of our different concentrations and our different levels of pH buffers we only changed the independent variable. We did this by altering our concentration level and pH buffer and kept all of our equipment the dame with thorough washes and dries after each test to keep the conical flask clean and fair. We had a fairly large error bar due to an outlier result which was far too high at the concentration of 100% we decided to keep this as our third result as we didn’t have time to repeat this test. We timed and recorded at the same time for each test allowing us to have accurate and reliable results.
Averages
Conclusion:
Looking at our graphs and tables we can see that our evidence is very conclusive, showing that the higher the concentration the better the reaction and as my graphs show the optimum concentration for the most oxygen to be produced was the 100% concentration of hydrogen peroxide as it produced the most oxygen at the end of the experiment, 193 cm³. This has been backed up from secondary sources which include the collision theory. The collision theory is when the concentration of substrate is increased; the more collisions can take place with the liver. This also changes the rate of reaction; this is due to the concentration. As the concentration of hydrogen peroxide increases, there is more to react, however, when the concentration decreases, the rate of reaction decreases, this is due to the amount of distilled water in the substrate. However, this does not mean that the reaction will keep going, as the rate of reaction increases, the less time it takes for the saturation point to be reached. The saturation point is the stage at which no more of a substance can be absorbed into a vapour or dissolved into a solution. Even if the amount of substrate is increased, there will be no more reactions. The rate of reaction can also be affected by the temperature. The temperature causes the movement to increase, therefore causing more collision to occur which increase the amount of reactions. This produced a lot more oxygen and water than the other concentrations.
Our results show that the higher the concentration of the hydrogen peroxide the better the reaction is, this is due to the fact that there are a lot more molecules to collide with the catalyse source, reacting to produce more oxygen and water. We had a number of outliers in our tables so in my averages I decided to not include them as they are obviously not reliable nor are they accurate, this may be because we measured a solution wrong or didn’t had our equipment set up properly.
With the 40% concentration, we can see that the experiment for this was the most equal and a fair test. This is shown by the line being straight and not curved like the others. This also shows that throughout the experiment, the rate of reaction didn’t change.
We changed our volume of molar from 10 to 20 voles from the pre-test to the main test so that the reaction would take place more vigorously and we would see result quicker and at a more varied state across the different concentrations. The rate of reaction was (at 120sec): at 100%-1.892cm³ of O2 per second, 80%-1.275cm³ of O2 per second, 60%-0.792cm³ of O2 per second, 40%-0.567cm³ of O2 per second, 20%-0.05cm³ of O2 per second. The rate of reaction shows us how quickly the 100% concentration reacted with the catalyse source. Our dependant variable is the amount of oxygen produced showing us the best concentration that collided the most with the catalase molecules. Our independent variable in the main test were the different concentration levels of the hydrogen peroxide mixed with the distilled water at different percentages; 20, 40, 60, 80 and 100 the solution altogether always added up to a total amount of 20cm³.
From the pre-test we decided to wait for 90 seconds again to let the reaction start occurring and gave it a chance to start producing more oxygen so that we can record our results from the start above zero. The lowest concentration and highest concentration suffered because of this as we found that they started to get to the point that the reaction would not take place anymore before we could record the results until this point so were unable to show their rise of O2. This is because the enzymes have reacted with the liver as fully as possible. I think that we used too much mass for our liver as we had to push the delivery tube back to zero several times letting the gas escape from the conical flask before we could reattach it. This made the test for the higher concentration unreliable. The graphs and results show us that as concentration of the hydrogen peroxide decreases there are fewer molecules to collide with each other producing less oxygen and water. On the other and when we used a higher concentration we noticed that there would be more molecules to collide with each other allowing a production of oxygen and water to increase.
Evaluation:
From our Pre -tests, we knew what we had to do, if anything were to happen. This was especially important with the gas syringe, because when the oxygen level reached 100cm³, we had to unplug the syringe, push back the syringe and then plug this back into the conical flask. We had to perform this routine several times, and this affected our end result. This didn’t change the result massively; however it was enough to change it by a couple of cm³, which would have a knock on affect on the average results. This could be improved for later tests using this equipment, by using a bigger syringe, meaning that less movement of the syringe and conical flask would be necessary.
To make my procedure better I would try to keep all of my measurements completely accurate putting in and testing only the correct amount of the sources(catalyse and hydrogen peroxide). This would allow us to have better result and cut out the outliers and reduce the size of our error bars on our graphs. Although some factors affected our results and test we managed to keep our procedure reliable by sticking to the same jobs throughout so that all of our practice would be in use and lead to a more reliable set of results.
As the results weren’t always roughly the same, we had to consider why these were way off the average results. As I have said before, the gas syringe may have changed the result at the end by a couple of cm³; however this would not have affected the end result by this much. We should also consider the temperature in which the experiment took place. The temperature can be affected by many factors, including the temperature of the room, the time of day, and the temperature of water we wash the equipment in. These all contribute to the end result and all could be watched when doing the experiment. We did the experiment at different times of the day; this would affect the room temperature. In the mornings, the radiators would not have been on for as long as at the end of the day, this may have affected the end result. Also which may have changed the temperature is the temperature of water that we washed our equipment in. In our experiment, we didn’t keep track of what temperature of water we washed up in, this could have been a contributing factor of these outliers and keep a fair test. This is especially important when washing the conical flask as this is what the chemical reaction will take place in. It is important to keep the temperature the same as different temperatures have different rates of reactions.
If I were to do the test again I would either use a smaller amount of catalase source or use a larger gas syringe to measure the oxygen with. To change the source of catalase I would us yeast this is because it has a better, more even surface area and you could measure it easier on the scales, I would change the source further by using only half a gram for the experiment as this would allow us not to push the gas syringe from 100cm³ to 0cm³ losing valuable cm³. I would also try and increase the size of the gas syringe for the same reason making the results much more accurate and fair. This would allow us to have results which were much more accurate but may affect the range of results given by the different concentrations. We would also record the results straight away rather than leaving it for 90 seconds until we start to record down the amount of oxygen produced. This would allow us to see the slow and steady build up of oxygen in the gas syringe until the saturation point were the reaction would stop taking place. We managed to weigh out the solutions well and the mass of liver extremely well so our independent variable was the only thing that varied keeping the test fair allowing us to have very reliable and accurate results. The only thing that we would try and change next time we did the result was the surface area of the liver so would try and blend the liver in a blender allowing us to have an identical surface area for each of the different concentrations.
Together the three of us in our group allowed to keep the same job for each experiment so I weighed the liver, Jack recorded the results down and Tom measured the substrate concentrations and pH allowing us to complete the experiment with more accurate and more reliable results having even less chance of faulty change for each result. This was confirmed as we compared our error bars and averages to the other class members showing that our results were correct and our error bars were small. We followed our method properly keeping to the health and safety aspects at all times and staying alert writing down any notes on the changes of each of the experiments. This allowed us to keep a record of what happened at the time when it happened so were not working by memory but on valuable and reliable notes.
After looking at the error bars for the experiment, we can see that the experiment we have done for the 20% concentration was extremely reliable. However, as the experiments went on, the results became further apart, which suggests that the experiments we performed on the other concentrations were not as reliable as they could have been. These could have been caused by the different factors which were talked about earlier. Despite the size of some of the error bars, the general trend still follows the theory. If we had more time, we would have repeated the experiments again, so we would not have any outliers. This would have made the results more reliable.
The conclusion is based around the collision theory; this is most reliable theory to explain the test that I have completed. This theory makes my conclusion very reliable as most scientists agree with the facts produced alongside the highly tested collision theory and as I have explained in my conclusion it is the theory of the collation between the molecules producing the reaction.
Working completely in our group of three we managed to complete the task to our full potential, this allowed us to see the changes occurring as we changed the different concentrations of the ph buffer and of the concentration of the catalyse source (which I would change if I were to do it again).