Use a Catalyst
A catalyst reduces the activation energy in a reaction. This means more particles have enough energy to react.
A good thing about catalysts is that they are never used up by the experiment. This means they are reusable and do not have to be bought again. This means that the catalysts are not in the equation either.
More About Catalysts
There are two types of catalyst.
Homogeneous Catalyst – They are in the same phase as the reactants and are in close contact to them. This means that they are very effective and cause a different route for the experiment easily and so lessens the activation energy. The problem with this though is that they must be separated after the experiment, usually by distillation.
Heterogeneous Catalyst – These are not in the same phase and are usually solids. These do not have much surface area exposed so are NOT very effective but are easy to separate from the products. They are very expensive also.
Prediction
I predict that changing the concentration of the Hydrogen Peroxide will make the rate alot slower. This is supported with the information on the last few pages. The less the concentration, the more space between the particles and so there will be less collisions meaning the rate will be less. Also, I predict that all the reactions we do today will become slower in rate by the end, as there will be fewer particles to collide so often as most would have reacted in the beginning.
This is also backed up by previous experiments, for example, an experiment with Thiosulphate and acid.
Na2S4O4 ----> S(s) + SO2 (g) + H20 + Na2SO4
We reacted the reactants in a beaker and placed it on top of a piece of card with a black cross on it. When the cross was invisible through the reactants we stopped the timer.
The results were as follows:
As shown in this experiment, as the concentration was diluted, the rate decreased. I believe a similar occurrence will happen in our experiment.
Strategy
The reaction produces oxygen. We can use this to our advantage either in two ways. A) We could find out how much of this gas is produced in a certain amount of time, or B) Find out how long it takes for a certain amount of gas to be collected.
Apparatus
2 Measuring Cylinders – To measure the chemicals,
Chronicle Flask – For the reactants to be contained and mixed,
Water bath – To contain water so as the oxygen can reach the top of the delivery tube,
Stop watch – To time the experiment,
Set up the apparatus as shown below:
>Oxygen
Delivery
Chronicle Flask Tube
Hydrogen Peroxide
ManganeseOxide Water
Method
- Place Safety Glasses and Laboratory Coats on
- Set up the apparatus
- Measure the appropriate volumes of water and hydrogen peroxide found in the table.
- Measure out the correct mass of Manganese dioxide.
- Place them together in the chronicle flask.
- Immediately start timing.
- Collect the results in a table.
- Do again with the next measurements.
- Make a graph from the results
- Finally find the gradient, which is used to find the rate of the reaction
Fairness
To keep this experiment fair, we will keep certain variables constant throughout the experiment, we will take atleast 5 readings to ensure an accurate graph, we will alter the dilution by adding and removing in 5cm2’s to keep a constant change. We will also repeat certain tests.
There are certain factors that MUST be kept constant, and some that are to be changed. They are shown on the next page
Results
Finding the Rates of Each Concentration Using Gradients from the Graphs on the Last Pages
25mls Water and 5mls Hydrogen Peroxide
X= 60, Y= 12, rate = 12/60 = 0.2
30mls Water and 5mls Hydrogen Peroxide
X= 45, Y= 9, rate = 9/45 = 0.2
35mls Water and 5mls Hydrogen Peroxide
X= 75, Y= 13, rate = 13/75 = 0.17
40mls Water and 5mls Hydrogen Peroxide
X=75, Y= 14, rate = 14/75 = 0.01
45mls Water and 5mls Hydrogen Peroxide
X= 45, Y= 14, rate = 14/45 = 0.32
50mls Water and 5mls Hydrogen Peroxide
X= 60, Y= 10, rate = 10/75 = 0.13
Using these, we can now make an overall comparison on all the concentrations’ rates. The graph of this is on the next page.
Conclusion
The rate of the reaction is proportional to the concentration of the Hydrogen Peroxide. The less the concentration the rate decreases in speed and takes longer. We also found that the rate decreased in each concentration towards the end.
Justification
The reason for this is because when a concentration is high, the particles have less space between them, so they collide more often, meaning that more are successful. The reason why the rate always slowed down towards the end was because, as the reaction went on, fewer particles were there to collide as many have already reacted. This means that more space was between the particles and so collisions were not as common. This is as predicted in the prediction.
Problems
Errors
Reliability
To make sure if our results are reliable, we can re-do the experiment to double check our results but we did not have enough time to do this.
There are many ways we could improve our experiment. We could have used an electric water bath that kept the temperature at a constant temperature for example. We could use a computer to measure the amount of oxygen left at the start to make it more accurate than our sight allowed. We could also have extended the amount of results to see if the rate slowed down.
Further Work
If we had more time, there would have been alot more useful information that we could have gained. We could use other concentrations of Hydrogen Peroxide to test if this affected the rate even further or we could use other acids completely.
