Surface area
If the chemical is a solid piece, some particles are hidden inside. Breaking it up means that more particles are exposed to collide and react.
Catalysts (including enzymes)
These speeds up reactions by lowering the energy needed for a collision to result a reaction. But they still need to meet up with the particles for the reaction to happen, so the above things (temperature, concentration and surface area) can still have an effect.
Aim:
I’m going to investigate the effect of the change in surface area of potato chip in a reaction with Hydrogen peroxide. For example if the surface area changes, will the speed of reaction change?
Prediction:
I’m going to put a piece of potato in hydrogen peroxide and see in how long fifteen bubbles of oxygen come out of the tube. I will measure the time in which the fifteen bubbles come out. Then I’ll cut the potato into smaller pieces and then count the bubbles. I think when the potato is cut into smaller pieces the bubbles come out quicker. This means that when you cut the potato you increase the surface area of the potato and the reaction will happen faster.
Apparatus:
6 test tubes Borer
Hydrogen peroxide 20ml for each experiment
Delivery tube Measuring cylinder (ml)
Stopwatch (sec) Bung
Ruler (cm) Potato
I set up the apparatus as shown in the diagram below.
Method:
Step by step method
- I purred 20ml of hydrogen peroxide into each of 5 test tubes.
- I cut out a piece of potato with a borer and took 4cm of it.
- I purred some water in the test tube and set up the delivery tube and bung.
- I dropped the first 4cm potato and quickly put on the bung.
- I shock the tube once and started taking the time.
- I started counting after the first bubble.
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When the 15th bubbles came out I stopped the time and written the results.
- For the next one I got the next tube with 20ml of hydrogen peroxide and did the whole process again with 4, 8 and 16 pieces of potato.
Safety:
To keep safe in this experiment you shouldn’t:
- Keep your head or eyes too close to the hydrogen peroxide.
- Wear goggles when using hydrogen peroxide.
- Put your hand behind the potato while cutting it with borer.
Fair test:
For making this test a fair one we will have to keep these measurements the same:
- The amount of hydrogen peroxide. (20ml)
- The size of the potato chip. (4cm)
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The volume or the amount of the bubbles. (0.8cm³) Or (15 bubbles)
I must change the surface area of the potato each time I do the test. This means that I have to chop the potato diagonally in half.
Results:
In the 1st and the 2nd round of the experiment, I had to redo the process because the difference of the results was high and I wasn’t sure. I have worked out the average time. For the surface area I used a special formula to work it out:
S/A= 2π r l + 2n π r²
But I used a simpler version of the formula above:
S/A= 8π(40+ 4n)
Volume of the oxygen bubbles, resulted by the reaction is 0.8 cm³. I had to divide it by the average time taken
Analysis:
I plotted the graph with the results I had from the table above. I drew a line of best fit to make it much more easier to read evaluate.
Conclusion:
According to the graph as the surface area is increased, the rate of reaction level rises as well. This is because as the surface area increases, more chance of the catalase colliding with hydrogen peroxide is provided. The more collision in an amount of substances the faster the reaction happens. The results of this experiment match the predictions I gave before the experiment (Look at 2nd page), because the experiments did before and now prove that, more surface area allows the reaction to happen faster and more efficient. I could have improved the experiment by using bigger chips of potato, because cutting a 4cm potato into 16 pieces was hard and may have come out inaccurate. The concentration of hydrogen peroxide could be increased to fasten the experiment.
Evaluation:
The results from this experiment are quite reliable, except the fact that some inaccuracy may have happened during the experiment. This could affect the graph and change the results. I had some problems during the experiment, chopping the potatoes, especially when I had to chop it into 16 pieces. I think the last one that we did was a bit unreliable, as you could see in the graph, all the other ones are in quite a straight line and the last one is out of the rhythm. I think this is because the cutting of the potato in cross sections wasn’t done properly, as you could see in the picture below:
At the 1st and the 2nd time on the graph I came up with the wrong results, which I highlighted with red and excluded them from the average. This was because the potatoes I used were not cut fresh. They were cut and left aside for the other experiments, therefore the catalase around the outside of the potato was damaged and this caused the reaction to slow down. This could be improved by cutting the potato chips fresh.