Does changing the concentration of Hydrogen Peroxide have an affect on the rate of reaction.

Concentration of Hydrogen Peroxide (cm³)

Concentration of water (cm³)

Volume (cm³)

Temperature (°C)

Size of potato (cm)

st Time (s)

2nd Time (s)

20

0

20

25

cm × 0.5cm × 0.5cm

60

73

0

0

20

25

cm × 0.5cm × 0.5cm

18

13

Preceding the first experiment I decided on changing a number of things to do with the experiment. Firstly I decided to change the shape of the potato I was using as cutting the potato into cubes was not only time consuming but was also difficult to get the correct measurements every time. By means of a cork borer I was able to get an exact diameter and surface area every time. I then only had to cut the length of potato to the right length. I decided on this to be 3cm for the main experiment. I also changed the method slightly since I found that when timing the experiments that involved a low concentration of Hydrogen Peroxide in the reaction it took a long while to get 10 bubbles. To make the time fixed I instead timed only for 2 minutes and simply counted the number of bubbles produced in that time. This way I would always know how long the experiment was going to last.

To ensure that the experiment is a fair test I will need to keep a number of different things the same. Firstly I shall need to make sure that for each experiment the amount of Hydrogen Peroxide that I intend to use is measured out accurately so that no experiment has an unfair disadvantage or advantage over another. I will do this by making sure that the base of the meniscus in the measuring cylinder is on the reading that I want. I will also make sure the surface area of the potato is kept constant by using cork borer 2 to impale the potato and then cutting it to exactly 3cm. If this is not done accurately then some potatoes will have larger surface areas than others will and the experiment will be biased. It is also important to keep the same potato throughout all the potatoes will be different to one another. Secondly I will need to keep the temperature of all the apparatus constant mainly the test tube in which the reaction is taking place so that the heat from my hands does not affect the Catalase and in turn the reaction rate. To control this variable, the temperature will need to be maintained at a fairly steady level so that the enzyme can work effectively (room temperature, approximately 23°C). I will also try to make sure that the table is not at any point nudged or moved or the solution disturbed as any of these could make the reaction go faster, slower or dislodge a bubble that was smaller than the rest and so make it an unfair test. I will make sure I am careful around the worktable so this can be avoided. Thirdly I will ensure that all equipment that has been used will be washed and dried before use again to avoid contamination. Finally, I will try to time the reaction as accurately as possible. There are no ways in which to help me do this except my own judgement.

It is necessary to control these factors as if they are not kept at the right level they can affect the position of equilibrium. To show how changing a factor can affect the rate of reaction and its position of equilibrium I have constructed a table below to indicate the condition and its effects.

Condition

Effects.

Temperature

Increasing temperature makes the reaction move in the direction which takes in heat.

Concentration

Increasing the concentration of one substance makes the equilibrium move in the direction that produces less of that substance.

Catalyst

Using a catalyst does not affect the position of equilibrium, but means the speed of the reaction n is faster.

To carry out the experiment successfully I will need a range of equipment. The apparatus I will need is listed below:

* Delivery tube

* Measuring cylinder (10cm³)

* Margarine tub

* Two test tubes

* Potato

* Potato borer 2

* Stopwatch

* Ceramic Tile

* Thermometer

* Ruler

* Scalpel

* Hydrogen Peroxide (20% conc.)

* Safety goggles

* Two bungs

* Test tube rack

Diagram

Method

(NB. Ensure safety goggles are worn throughout the experiment and that care is taken when handling chemicals.)

. Set up the apparatus as shown in the diagram above.

2. Using a measuring cylinder (10cm³) pour the following measurements into five separate test tubes. If this amount of equipment is unavailable then simply add the following into the same test tube before each experiment.

Test Tube 1 - (10cm³ of Hydrogen Peroxide)

Test Tube 2 - (8cm³ of Hydrogen Peroxide) (2cm³ of Water)

Test Tube 3 - (6cm³ of Hydrogen Peroxide) (4cm³ of Water)

Test Tube 4 - (4cm³ of Hydrogen Peroxide) (6cm³ of Water)

Test Tube 5 - (2cm³ of Hydrogen Peroxide) (8cm³ of Water)

3. Using Cork borer 2 obtain five lengths of potato each measuring 3cm long.

4. Place Test Tube 1 with contents into a test tube rack with the delivery tube out. Put one cylinder of potato (prepared earlier) into the Hydrogen Peroxide and replace the bung attached to the delivery tube to test tube 1 as quickly as possible.

5. Once the first bubble has left the delivery tube start the timer.

6. Observe how many bubbles leave the delivery tube and note down each one that surfaces.

7. Stop the timer once the time has reached 2 minutes.

8. Record the final values in a table.

9. Repeat steps 4 - 8 again but instead use test tube 2, then after that test tube 3 until all have been analysed.

0. Once the initial experiment has been done repeat steps 2 - 8 twice more so that you have three complete results tables at the end.

I have chosen to repeat the experiment 3 times because it therefore allows me to calculate an average time. This will ensure that there are no abnormal results and it will increase accuracy. I have decided to start the concentration of Hydrogen Peroxide at 10cm³ and decrease the concentration by 2cm³ each time since it will allow me to see the increase and decrease of the enzyme activity. It should also be accurate enough for me to predict an optimum concentration within 1cm³.

To ensure safety in the experiment care was taken when handling chemicals in particular Hydrogen Peroxide as it is corrosive. Whilst using the scalpels, care was also taken to hold them by the handle and not the blade to prevent an accident occurring. Goggles were worn during the experiment for protection against the chemicals.

Skill Area O: Obtaining Evidence

Table 1 - Results

Concentration of Hydrogen Peroxide (cm³)

Concentration of water (cm³)

Volume (cm³)

Temperature (°C)

Size of potato (cm)

No. of Bubbles (1st test)

No. of No. of

Bubbles (2nd Bubbles (3rd)

test) test)

No. of Bubbles (3rd test)

Length (cm)

0

0

20

22

Cork Borer 2

3

1

17 16

6

8

2

20

22

Cork Borer 2

3

7

10 13

3

6

4

20

22

Cork Borer 2

3

2

9 10

0

4

6

20

22

Cork Borer 2

3

3

8 10

0

2

8

20

22

Cork Borer 2

3

7

6 7

7

Graphs - Results

The following graphs illustrate the results that I acquired during the experiment. Unlike the results table they give an indication of what would have happened in between the set concentrations of Hydrogen Peroxide e.g. it is possible to estimate how many bubbles would have been produced if 5cm³ of Hydrogen Peroxide and 5cm³ of water had been used with use of an accurate graph.

Table 1

Table 2

Table 3

No. of Bubbles (1st test)

No. of Bubbles (2nd test)

No. of Bubbles (3rd test)

AVERAGE

1

7

6

6.5

7

0

3

1.5

2

9

0

0.3

3

8

0

9

7

6

7

6.6

Results shown in red are anomalies and have not been included in the averages.

In the preliminaries I decided to use potato cubes of 1cm × 0.5cm × 0.5cm. After cutting the correct dimensions I found that it took a lot more time than simply using a cork borer and then cutting the appropriate length. I reverted to this alternate technique when doing the final experiments. I used cork borer two and then cut the potato cylinders to 3cm long. Another change I made involved the way I counted the bubbles. Instead of timing how long it took to get 10 bubbles I instead selected a fixed time, being 2 minutes and then counted the number of bubbles produced during that time.

As a precautionary measure to make the experiment more accurate I made sure when measuring out fluids that the base of the meniscus was on the reading that I wanted. As well as this I made sure to use the same potato throughout for added accuracy.

Skill area A: Analysing and Considering Evidence.

In conclusion to the experiment I can see from the graphs in particular one & two that the most oxygen was produced in the shortest time using 20% concentration of Hydrogen Peroxide. This is evident by the steep gradient that can be seen between 0 & 4 cm³ of Hydrogen Peroxide on the graph. The graph then starts to level off resembling a decrease in the reaction rate again rising between concentrations 14 - 20 cm³ on graphs 2 & 3. The third and last two concentrations on graph 1 appear to be a series of anomalies which undermine my prediction as they state that the rate of reaction is higher using 8cm³ of Hydrogen Peroxide rather than 12cm³ and 16cm³ is faster than using 20 cm³ which of course is incorrect. Graphs 2 & 3 both support my prediction as they show the higher the substrate concentration was the more oxygen was produced. As you can see from the graph, at low substrate concentrations the rate of reaction is relatively proportional to the substrate concentration because when the substrate concentration is increased the rate of enzyme-substrate collisions (reaction) is equally increased. Conversely, as the substrate concentration rises the rate of reaction will finally reach a maximum level. This is because all of the active sites are saturated with substrate and the rate of reaction or products produced by the reaction will increase no further.

However, the point at which the reaction reaches its maximum level is not shown on my graph because we did not reach that far in our tests. These ideas relate to the concepts of collision theory and enzyme theory.

Skill Area E: Evaluating

One area in which I had no control over in was deciding which apparatus that we would use. The measuring cylinder we used held 10cm³ of liquid which was perfect for our use as we only needed to measure out this amount for each experiment. Using a burette or a pipette of fixed volume would have been a more accurate way of measuring out the liquids but this equipment was unavailable hence the use of a measuring cylinder. The stopwatch that was used was perfectly accurate. Although it was a budget school model I doubt there would have been any discrepancies in its time keeping. I however found it difficult to stop the stopclock at the exact time in which the bubble left the delivery tube. This will have affected the results but not so much as to make them greatly inaccurate. The thermometer that was used was fairly accurate and although as the stopclock was not an expensive model it did the job and provided a relatively accurate temperature This is also the case for the ruler I used to measure the lengths of the potato.

In terms of quality, my results overall portray a fairly accurate synopsis of what would have occurred in a perfect situation. My prediction, based on fact that I was already aware of was backed up by my results, however the first experiment that was carried out went wrong due to a unknown fault and so affected the way I which I looked at the other sets of results. If had I not done three experiments then I would have been unable to tell which set of results was incorrect due to the inaccuracies that I faced in the initial experiment. In the first experiment I had three anomalous results being the third, fifth and sixth. In no other experiments did anything else go wrong. Although I am not sure of the exact reason why these occurred it may have been due to a variety of reasons. One possibility could be that fluctuations in temperature caused the rate of reaction to increase or the delivery tube to expand, forcing the bubbles out at a higher rate. Although minimal contact was made with the apparatus during the investigation, slight undetected variations in the room temperature may have led to inaccuracies.

The method I devised was suitable for testing my prediction because it explored all aspects of varying concentration and was for the most part accurate. When the results were obtained the accuracy of them brought about an agreement with the prediction and this confirmed that the procedure was suitable.

The first experiment that was done was for the majority very inaccurate. The second and third experiments showed a trend in results and confirmed a good set of accurate results. This was backed up by the similarity of the two graphs. The main reason for the inaccuracy of the first was down to the various bottles I used acid from. Owing to my placement in the experiment I was last to get hold of any equipment, I had to change the Hydrogen Peroxide that I used frequently because many bottles were nearly empty and so I was forced to take a small amount from each. This could have seriously affected my first experiment as some acids may have been more or less concentrated than others may. To eliminate this problem using a larger bottle containing acid would be appropriate so that there would be no change in the quality of the chemicals I was using.

I gained enough quality evidence to support my prediction throughout the study although the first experiment could be considered a flop despite the fact that we gained only three anomalous results. I am happy with the way in which the tests were conducted and also the results that were found. To carry out, the tests were enjoyable and everything ran smoothly throughout the experiment. Apart from the irregular results the experiment was practically faultless.

There are several sources of possible error in the results of this investigation and there are many suggestions that may reduce these inaccuracies and improve further investigations in the future. If done these suggestions could provide additional relevant evidence to back up my conclusion and extend the investigation.

i) Readings - Due to time restrictions in this investigation, I was only able to take three readings at each substrate concentration. These readings were then averaged so that the extent of any anomalies would be minimised. However, to ensure that accurate results were being obtained a larger number of readings should have been taken. In a future investigation, I would recommend that at least five readings should have been taken at each temperature variation to gain the best results and most accurate graph.

ii) Variation of substrate concentration - In this investigation, I measured the rate of bubbles per every two minutes, at varying substrate concentrations. These concentrations were 2cm³, 4 cm³, 6 cm³, 8 cm³, and 10 cm³ of Hydrogen Peroxide. Although this is a fairly good range of concentrations, it is still difficult to conclude a decent idea of how the substrate concentration can affect the rate of reaction. To gain the full picture one must carry out a greater range of tests to investigate the number of bubbles produced up until the point where the reaction can produce no more oxygen and down to the point where no reaction happens at all.

iii) Accuracy of measurements - When carrying out the tests I was forced to assume that all the bubbles consisted of the same amount of oxygen. This, as I was aware of, was not true but having no control over this aspect of the study disabled me from being able to rectify the problem. In a future investigation I would advise the use of a gas syringe to measure the amount of oxygen that is produced rather than counting the bubbles, because as long as the equipment is accurate then the results will be a lot more also.

iv) To widen my range of knowledge on enzymes and their properties especially Catalase it would be useful to investigate other variables, enzyme concentration, temperature, pH to name a few. Other studies that involve for example investigating the factors that affect the activity of the enzyme Amylase or Sucrose for instance would also be a idea to work on in the future.

James Black

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