The faster the particles are going, the more energy they will have. Fast moving particles are more likely to react with each other, because they collide with a stronger force and break bonds easily, and so will react a lot faster. Referring to my factor that I will be investigating, particles will move more quickly if they are heated, which will be achieved by raising the temperature.
Diagrams to explain my background knowledge.
Before I can go on I have find the best possible way of measuring the rate of decomposition.
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Change in mass over a period of time – this would be carried out on a balance. As the gas from the reaction is given off, the mass disappearing over a period of time can be measured and recorded.
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Rate of precipitation – This is only possible when one of the products of the reaction is an insoluble solid which forms as a solid in a solution (a precipitate). The solution gradually becomes more and more opaque, and so the reaction is set up in a flask over a piece of pare with a cross marked on it. The time taken for the mark to disappear is recorded. This is not possible with this investigation.
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Volume of gas – The gas given off is collected in a gas syringe and the volume of gas is recorded.
I am going to measure the volume of gas given off within a certain time.
After considering how I am going to measure the rate of decomposition, I am now going to do some preliminary experiments. These will allow me to find the right amounts of products to use and how to do fair testing.
Method for the Preliminary experiment
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30cm³ of hydrogen peroxide will be put into a boiling tube and 1g of manganese(IV) oxide will be added.
- The bung from the gas syringe will be placed on top directly after the manganese(IV) oxide is added.
- A stopwatch will be started and for 15 seconds and my helper will read off how much gas is collected when I say stop after 15 seconds.
This is the method that is going to be followed, however many trials were done with different amounts of hydrogen peroxide and manganese(IV) oxide, and also the temperature was increased. This is going to be done by using a thermometer to see the temperature of the hydrogen peroxide at room temperature, and also after heating the hydrogen peroxide a little to get a different temperature. The different trials are stated below in the following table.
From those trials I can conclude the following:
- In the first experiment too much gas was produced in 15 seconds, therefore the time must be reduced.
- Between the second and third experiments I decided that the amount of solution was too much and that was the reason so much gas was being produced in the first experiment.
I then went on taking the information above into account, and did some more preliminary experiments with a few changes to the method. I changed the amount of time to 5secs because 10secs was producing too much gas. Also changed the amount of manganese(IV) oxide added to 0.5g because that way it would allow me to do another set of experiments to make sure I do a fair test for my actual practical.
The second sets of preliminary experiments are in the table below.
From this second set of preliminary experiments I found out the right amounts that I wanted to use, which are now stated in the method that I used.
List of apparatus I am going to use
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250cm³ of Hydrogen peroxide
- 5g of Manganese(IV) oxide
- 5 boiling tubes + rack
- 5 weighing boats
- Gas syringe + clamp and stand
- Bunsen burner
- Thermometer
- Stopwatch
Method
- I am going to first set up my gas syringe by clamping it, because it will be a lot easier to place the bung on after adding the manganese(IV) oxide.
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I am then going to measure out 25cm³ of hydrogen peroxide into 5 boiling tubes each, and set them in a rack.
- I will then measure out 0.5g of manganese(IV) oxide into five weighing boats, one to add to each test tube of solution.
- I will then light my Bunsen burner and collect a stopwatch.
- I will then take a thermometer and record the room temperature of the solution. I will add in the manganese (IV) oxide and place the bung from the gas syringe on and start the stop watch. Whilst this is going on I will shake the contents of the boiling tube, as the reaction will only occur on the surface. This would produce unreliable results, as not a lot of gas may be given off and so the catalyst needs to work with all the hydrogen peroxide, for this to work fairly.
- After 5secs I will say stop and my help will read off the amount of gas that was collected.
- This will be repeated for the remaining four test tubes however, they will be heated to different temperatures which will be recorded
To make this experiment a fair test I will not change any factors except the temperature of the solution. The results of my experiment are stated on the next page.
OBTAINING
Results (1)
Another set of results was taken because I repeated the experiment with the left of equipment.
Results (2)
The results were then taken and averaged, shown in the next table.
The results were then plotted on the graphs, on the following pages.
Key
X = results for table 1
X = results for table 2
Gas given off was tested by placing a glowing splint into a test tube of that gas. The splint was relit.
ANALYSING
From the results in each of the tables you can clearly see that as the temperature rose, so did the amount of gas collected within the 5 second time period. Once plotted on the graph you can see the result more visually. The curve of best fit supports my conclusion from the tables and my hypothesis. As the temperatures rises the curve becomes steeper, showing the increase in gas given off. Therefore, from all this you can see that the rate of decomposition was increasing as the temperature also increased.
To explain this I can refer back to my scientific knowledge. As the temperature was increased, the particles were given larger amounts of energy. This meant that the particles were increasingly colliding faster and stronger and as the result the rate of decomposition was steadily increasing. For example, at room temperature the particles did not have as much energy as they did at 32ºc, and so were not colliding with each other as much. Also there is a higher chance of collision as the temperature increases.
The graph that shows the average set of results also supports my hypothesis. As the temperature increases, the decomposition of hydrogen peroxide increases, because the particles collide more frequently breaking bonds, which then cause the hydrogen peroxide to decompose.
The curves that were drawn on both graphs lie around the same place; this goes to show that both sets of experiments were close in results. This shows the amount of accuracy I tried to put into making sure my results were fair. Also both curves have the same steepness and so this also shows how accurate my calculations were.
The gas that was collect relit a glowing splint. This is the test for oxygen, and so I can come to the conclusion that the gas collected at each stage was in fact oxygen. This proves that the hydrogen peroxide was decomposing to produce the element oxygen and water, as a result.
Hydrogen peroxide + Manganese(IV) oxide → Oxygen+ Water + MnO2
2H2O2 (aq) MnO2 (s) O2 (g) 2H2O2 (l)
The manganese(IV) oxide that was added was able to speed up the decomposition of the hydrogen peroxide fast enough to be able to collect the amount of gas that was given off.
EVALUATING
The method that I used, did indeed give me clear enough results to have been able to come up with a conclusion that supported my hypothesis. The results were reliable to a certain extent that they were not as accurate as possible, but this is likely to happen. They can however, be counted on as correct because they do prove my hypothesis to be correct and support the theory of increasing the temperature which increases the rate of reaction, or in this case the rate of decomposition.
The graph that was plotted as a result of my two experiments shows how reliable my results are. However, there are some anomalous results, which have been circled. Although none of my plots lie directly on the curve of best fit, this was to be expected because when measuring the amount of gas collected, or even the change in mass, there are bound to be some errors.
In my case, the reason for the anomalous results, or the fact that the plot do not lie directly on the graph is that the time between adding the manganese(IV) oxide and placing the bung on from the gas syringe some gas was lost. Each time I repeated that step some gas was lost on account of it is almost impossible to add the manganese(IV) oxide and place the bung on at the same time. Also from the table you can see how the temperature for both sets was not exactly the same. For example, the first time the room temperature was 22ºc and the second time it was 21ºc. This was because they were done on different days, showing that day 2 was colder and so my room temperature decreased slightly. Also the temperature that was shown on the thermometer kept on changing. For example, after heating it to 25ºc, it rose up to 27ºc, and this is why my temperatures do not match exactly but are close. This also shows that my fair testing did not come into practice too well. As to have made it fairer I should have done both sets of experiments on the same day.
The largest error made was between the last two plots on the graph. At 42ºc 50cm³ of gas was collected, whereas on the second day at 39ºc 55ºc of gas was collected. Again this is due to the faults I stated about that could not be avoided.
The graph that shows the average set of results shows that the plots lie directly on the curve of best fit. This shows that despite the minor errors made between the two experiments, the average shows a reliable set of results, which erases all the anomalous results shown before.
Taking into consideration that the method did produce a reliable set of averaged out results, to make this experiment more reliable in the future I can:
- Do all sets of experiments on the same day, to improve my chances of gaining fairer results
- The time between adding in the manganese(IV) oxide and placing the bung on top could be reduced by having both sets of apparatus closer together.
- I could have done more temperatures, some higher than the one I stopped at and maybe even some lower to get more sets of results. This may prevent anomalous results happening and give a more precise average. Also this could support my scientific background to larger extent.
