6x 250cm3 Glass beakers – Where my 6 different concentrations will be stored.
6x Glass measuring cylinders – Will be used to measure out the 6 concentrations to a good degree of accuracy.
Thermometer – Used to try to keep temperature constant.
Pestle and mortar – Will be used to grind liver up to keep surface area constant.
Sand – Will grind liver up easily.
Stop watch – Will measure the time taken for the liver to break down the H2O2. To a good degree of accuracy.
Knife – Used to cut liver into small pieces.
White Tile – Where liver will be cut on.
Balance – Will weigh the liver to 2 decimal places more accuracy.
Syringe 10cm3 – Will be used to input the hydrogen peroxide into the test tube. Also measure the H2O2 to a good degree of accuracy.
Diagram:
For the experiment I will choose 6 different concentrations and do the experiment 3 times with each one. My variable is the concentration of the substrate which is the hydrogen peroxide. Reason for choosing this variable is because enzymes are affected by the concentration of the substrate. My concentrations will be:
The water and hydrogen peroxide will always make up 10 Cm3.
6 Concentrations I feel is more than enough to see how it affects the rate of reaction.
I choose these concentrations as the concentrations lower then these took a bit of time to get the reaction started. This was when I was doing some preliminary results.
Preliminary:
For the preliminary I choose the highest and lowest concentration so straight away I could get an idea of how the substrate concentration affects the rate of reaction.
Highest: 10 Cm3 Hydrogen peroxide.
Lowest: 5 Cm3 Water 5 Cm3 Hydrogen Peroxide
Preliminary results:
From this you can see that the highest concentration was quickest to react.
Procedure:
Put on protective clothing such as safety goggles, lab coat and gloves. First I will set up equipment appropriate as shown in the diagram. Using the knife I will cut the liver into small pieces on the white tile. After this has been done, I will weigh the liver on the balance to a weight of 2.00g. Next the liver will be placed in the pestle with some sand. Using the mortar I will grind the liver into smaller pieces. After this the liver will be transferred into a test tube. This will then be put into a test tube rack.
After I will then make my 6 concentrations. I will start off with my highest concentration which is 10% Hydrogen peroxide (10 Cm3). To make the other concentrations for instance my lowest add 5 Cm3 of hydrogen peroxide and the 5 Cm3 of water etc. Using the syringe I will collect my first concentration which will be the 10cm3 hydrogen peroxide (Highest). After the syringe will be placed onto the bung. The hydrogen peroxide can be inserted into the test tube with the liver when ready.
The liver needs to be at the bottom of the test tube. If not liver may be left un-reacted therefore it will not be a very precise test. An effected way is to use tweezers when placing the liver in the test tube. Next place the bung on top off the test tube. Make sure rubber tube is connected to the bung and gas syringe. After keep stop watch ready in one hand and then insert hydrogen peroxide from the syringe into the test tube. As soon as this has been done start the stop watch.
When the hydrogen peroxide is being broken down by the liver (catalase) oxygen is given off. The gas syringe volume will move up. When the syringe has stopped this is a signal to stop the stop watch. The time on the stop watch will be recorded in my table of results. The experiment needs to be done 3 times for each concentration.
Safety Precautions:
When using hydrogen peroxide safety precautions should be taken.
It is extremely corrosive which can cause severe burns and vapour can be irritating.
Therefore:
- Goggles and safety clothing should be worn.
- Gloves worn
- If spilt clean up
- If spilt on clothing change clothing
- And the knife
When experiment is redone:
Pestle and mortar need to be cleaned out because more catalase will speed up the reaction. Test tubes need cleaning out. Also the syringe needs cleaning out. These factors may cause inaccuracies if not followed. More catalase means more active sites so therefore rate of reaction will increase. I will need to keep the ph and the temperature the same.
Results:
Overall the reliability of my results is pretty reliable. However there is an anomalous in the 8 Cm3 concentrations as it is a lower value than the previous concentration. Other anomalous is the 1st time for the 10 Cm3 Hydrogen peroxide. This is a slight error with the timing. However you can still see a trend in the results. Precision is good. I worked out the average time by adding up all the 3 different times for each concentration and then dividing by 3. The limitations were that when the gas of oxygen being produced was inconsistent there for anomalies could have been down to this.
Analysis:
My results show a trend that as concentration increases so does the rate of reaction. The reaction is speeded up due to this. The 10 Cm3 concentration was broken down fastest due to all the enzyme active site being used therefore the enzymes are working at fastest rate. To also explain this, the higher the concentration the more collisions there were between the enzyme molecules and the substrate molecules. As concentration goes up so do the active sites.
The anomalous results could have been down to the equipment not being cleaned properly after each experiment. The equipment may have contained extra catalase therefore this will increase the number of active site for the enzymes causing the hydrogen peroxide being broken down quicker. Another factor was that the room temperature rose as the day went on. It was cool in the morning and then got hotter.
Temperature affects the enzymes and substrate by causing the molecules to move faster. This causes the molecules to collide more often. And therefore the rate of reaction was increased. This could be used to explain why the time for the lower concentrations was so small a measurement.
Surface area of the liver could have been a factor. The liver was not cut up equally so there for the larger the surface area the molecules have a bigger surface to work on. More useful collisions are made.
This could have also been down to human error where measurements were inaccurate. For instance the concentration of the hydrogen peroxide was measured wrong. Also equipment was not cleaned properly.
Considerations when doing the experiment again:
If I was to do the experiment again I would make sure that the equipment was cleaned properly. Also measurements are taken more accurately and precisely. I will have to make sure the temperature is constant throughout the whole experiment.
