To investigate what affects the rate of which catalase decomposes hydrogen peroxide.

GCSE Science

Aim

The aim of our investigation is to find out what affects the rate of which the catalase decomposes Hydrogen Peroxide.

Introduction

The reaction between the substance (Hydrogen Peroxide), and the catalase (potato), produces water and oxygen.

Hydrogen Peroxide catalase Water + Oxygen

2H2O2 catalase O2

Variables

There are 8 variables that we could have used. These are as follows: -

Temperature
pH
Concentration of enzymes
Concentration of substrates
Type of potato
Age of potato
Size of the cylinder of potato
Raw or cooked potato

The variable that we have decided to use is temperature, and I have put a little star next to it. We decided to use this because we thought it would be the easiest, and most accurate possible.

We were thinking of using pH as our variable, but we decided that it was too difficult to do and that it is more than A* grade work.

Prediction

I have predicted that the more the temperature is increased, the faster the rate of reaction will be. I think this because the molecules will leave and enter the active site faster. I also think there will be more successful collisions meaning that there will be more bubbles produced.

Fair Test

I will try and make the majority of things the same during the experiment, to make it as fair a test as possible. I have listed them below: -

We will keep the pH of the Hydrogen Peroxide the same.
We will keep the concentration of the substrate the same.
We will use the same potato throughout the experiment.
We will not cook the potato.

We are keeping the pH of the Hydrogen Peroxide the same because if we do change it, then it will act like a change in temperature, and this would affect our results.

We will keep the concentration of the substrate the same because if we do change it, there will be different amounts of molecules in the active site and this once again will change our results.

We will use the same potato throughout the experiment because if we used a different one, we couldn’t guarantee that the concentration of the enzyme would be the same and again it ...

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We are keeping the pH of the Hydrogen Peroxide the same because if we do change it, then it will act like a change in temperature, and this would affect our results.

We will keep the concentration of the substrate the same because if we do change it, there will be different amounts of molecules in the active site and this once again will change our results.

We will use the same potato throughout the experiment because if we used a different one, we couldn’t guarantee that the concentration of the enzyme would be the same and again it would affect our results.

We will not cook the potato because cooking it would denature the enzyme, and would kill off the cells.

Preliminary Work

Here are the results for the preliminary work we did, prior to the experiment.

The results of our preliminary work were to try and find out what the best and most suitable temperature of catalase and substrate to use was. From looking at our results we decided to use 200C-600C.

Apparatus

All of the apparatus that we need for our experiment is listed below: -

5 50cm3 measuring cylinders
5 100ml beakers
5 test tubes
5 boiling tubes
1 potato
1 delivery tube
1 stopwatch
Kettle
5 thermometers
Cork borer
Scalpel
1 beaker of ice cold water
1 beaker of boiling water
Safety glasses

Method

First of all we will collect all of the apparatus required for our experiment.

Use the cork borer to get 6 cylinders (1 spare) of potato.

Now that we have the 6 cylinders of potato, we need to cut them all to the exact same length using the scalpel.

Put 1 cylinder of potato into each test tube, leaving us with the spare piece, in case something goes wrong.

Now put 25cm3 of Hydrogen peroxide into each of the 5 boiling tubes

Now fill the 5 100ml beakers with there specific temperature of water.

Now put a test tube with potato in, into a beaker of water along with a boiling tube with Hydrogen peroxide in it.

Wait until the potato and Hydrogen peroxide have reached the temperature of the water that they are in.

Once they have reached the desired temperature, put the potato into the hydrogen peroxide, and immediately place a delivery tube on top.

Start the stopwatch, put the end of the delivery tube into some water, and count the amount of bubbles produced in the water for 3 minutes.

After 3 minutes is up, record the amount of bubbles produced into a results table.

Now repeat for the remaining 4 temperatures.

Accuracy

We always measure to the nearest second because our human reactions are not quick enough to be exact with the stopwatch and the result may not be very accurate, so measuring to the nearest second is more accurate. We made sure that the measuring cylinder was on a flat surface and that we look eye level on. If you are not on eye level with the certain point then you will not get an accurate measurement because of the parallax of the top of the liquid.

When there is a liquid in a tube the upper surface is curved so we always measure the lowest measurement of the liquid.

Sometimes when we do experiments we can make mistakes and you may end up with some anomalous results, so we repeat the whole experiment again once we have done it the first time. We have decided to use a 50cm3 measuring cylinder to measure the water and acid because it is best to use the lowest possible measuring cylinder. If we used a 100cm3 cylinder then it might not be as accurate.

Results

Here are our results from our experiment.

I have also drawn a scatter graph to show my results.

Conclusion

When we did our experiment we found out that the highest amount of bubbles was produced, when the temperature was at 300C. From point A on my scatter graph to the optimum, the amount of bubbles being produced increased. This is because the enzyme (potato) and substrate (Hydrogen peroxide) are having more successful collisions. This is because they are both moving faster, at a result of being hotter. From the optimum on my graph to point B the amount of bubbles being produced decreased. This is because the temperature is too hot and the active site is becoming distorted. If we were to carry on heating the substrate and enzyme we would eventually end with no bubbles being produced. This is due to the fact that the active site will be totally denatured.

Before we started our experiment we predicted some results and compared them to our actual results. They were reasonably close.

Evaluation

Overall, our results were accurate and in my opinion we chose the correct variable to use. We eliminated all of the variables apart from concentration of the catalase, which we were unable to control.

I think our experiment was very well done and our results were very accurate. We were sure that our results were accurate as we repeated the experiment twice and we got roughly the same results each time.

We had one anomalous result from our experiment. This was when there were 32 bubbles produced from a temperature of 400. There may have been a leak in the delivery tube that caused this to happen.
To make sure that our results were definitely accurate we could have repeated the experiment for a third time, but we did not have enough time.

A different type of method that we could have done was to collect the gas in a gas syringe instead of counting bubbles. This way might have been more accurate but we would have had a problem when the gas syringe was full, we would have had to empty it.

From my prediction, I was not correct in predicting that the hotter the temperature, the more bubbles were produced. I know fully understand why I was incorrect.