Reasons for the method
I decided to use 25cm3 of Hydrogen Peroxide because the breakdown of Hydrogen Peroxide by Catalase is quite vigorous and a substantial amount of oxygen may be produced. 25cm3 ensures that I will have enough time to record a trend on how long it took, and that all the results will not be bunched together.
I have decided to use 1g of liver because it increases the amount of Catalase available to convert Hydrogen Peroxide into water and oxygen, so producing a measurable amount of oxygen in a suitable amount of time.
The quick placing of the bung into the top of the test tube as soon as the liver has been added is to minimise the amount of oxygen not collected when the reaction starts. If the time took to put the bung in place was great some oxygen might be missed and not collected into the measuring syringe, so reducing the reliability of the results.
Filling the measuring cylinder with water makes sure that no other gases except the ones I will be collecting are present in the results. Since the rubber tube coming from the test tube is fed straight into the measuring cylinder it is only that gas from the test tube that is allowed to be measured. But if gas was already in the cylinder then the results would be hindered.
Leaving the water in the 200ml beaker to acclimatise ensures that the temperature of the test tube is at room temperature. This makes certain that the volume of oxygen produced is reliable by concentration of Hydrogen Peroxide alone.
A 50cm3 measuring cylinder has been used for collecting the oxygen due to the accuracy of the markings. They are good enough to allow sufficient precision in the readings taken.
Repeats are taken to increase the accuracy of the results obtained. If any inaccurate results are taken then the two accurate results reduce the inaccuracy on the average produced. It also makes it much easier to see anomalous results.
Six different concentrations of Hydrogen Peroxide are being investigated. This means the results can be plotted on a line graph with sufficient points to allow a trend to be identified. Too few points would make it hard to see the trend. Using a maximum of 6% concentration ensures that the chemical is not too dangerous to work with.
Factors to keep constant
Ensuring that the evidence is reliable and accurate
To make sure that the results are able to be compared the factors mentioned in the table above will be carefully upheld to throughout the investigation.
The taking of repeat readings will allow to me verify that the results are reliable and accurate. To do this, I will check the repeats to certify that the consistency is to an acceptable accuracy.
If any of the results turn out to be anomalous I will take a reading at that level of Hydrogen Peroxide concentration to deny of confirm the inaccuracy.
Since I have a belief of what results I should get, if any results seem to disobey this trend I can take that reading again to ensure that it is correct.
There are some possible times where error could occur in my experiment and if these are limited then the results are to be more accurate. Some examples in this department include:
- Making sure that the measuring cylinder is completely full of water and that no air is trapped inside before the collection of the gas.
- Making sure the scales are set to zero prior to measuring the mass of the liver. If they are slightly out then different amounts of liver may be processed.
Preliminary work’s influences
The plan above was based upon several experiments I conducted preceding the writing.
Firstly to see how much liver should be used. For this I used 10cm3 of 6% Hydrogen Peroxide. I used 10 because it is a nice round number. I also used 10cm3 collection of oxygen produced because again it was a nice round number.
I decided to go for 1g of liver to be used because using 0.5g of the substance led to results which were hard to be timed. So for accuracy’s sake 1g gave the best results.
I then decided to see what concentrations of Hydrogen Peroxide to use. The maximum concentration I could use safely was 6% so I was limited resource wise to this. To find a good trend at least 5 results are needed. Since 6% was the largest I decided to take 6 readings, each at an interval of 1%. I tested out 3 of them to see if they were far apart enough to set the trend. I used 1g of liver and took the time at a volume of gas at 10cm3
These results seemed plot able so I decided to stick with them and use them for the experiment.
I was then left to decide what volume of gas to collect. Since I was using a 100cm3 measuring cylinder at the time of the preliminary work I tried 25cm3 because it was a large figure but small enough not to take too long. 10cm3 had worked fine, but did seem too little to be using for the experiment.
I used 1g of liver and the concentrations of H2O2 stated below.
These results seemed to be good to plot so I chose to use them in the experiment.
Prediction
Since I had 3 rough readings of time for different concentrations of Hydrogen Peroxide I plotted them on a graph to see if a trend was forming so I could make a prediction.
From seeing this, I predict that as the concentration of Hydrogen Peroxide decreases the amount of oxygen produced per second will decrease. Therefore the time taken to produce 25cm3 of oxygen will increase.
