I shall be investigating how the variable of concentration affects the decomposition of Hydrogen Peroxide. I have chosen this variable, as it shall be easy to observe, alter and control. I shall alter the concentration of the Hydrogen Peroxide by adding different amounts of water to it in a solution, depending on the desired concentration.
Despite the use of the catalyst, Manganese (IV) Oxide, the decomposition of Hydrogen Peroxide is not affected. This is because the catalyst is kept at a constant throughout the investigation.
My hypothesis is that as the concentration becomes weaker, the longer the duration of time, for which it takes Hydrogen Peroxide to decompose. This is because if the concentration in the solution is weaker and there will be less chance of successful collisions between the particles of Hydrogen Peroxide and the Manganese (IV) Oxide due to there being less Hydrogen Peroxide particles.
Therefore I predict the results graph shall look as follows: -
To conduct this experiment I shall be using the following apparatus and equipment: -
Gas Syringe Hydrogen Peroxide Manganese (IV) Oxide
Retort Stand Clamp Water
Stopwatch Glass Beakers Cone - shaped Flask with cork
Measuring Cylinders
These apparatus shall be set up as shown in the diagram below: -
To perform this experiment I shall gather together the apparatus as stated in the Apparatus section, and set up the experiment as shown in the diagram.
Then I shall dilute the Hydrogen Peroxide in water to achieve the concentration I desire, 20%, 15%, 10% or 5%. This is because I shall be carrying out the experiment using each of the concentrations. Then I shall add the Hydrogen Peroxide and the Manganese (IV) Oxide together into flask attached to gas syringe. As I do this I shall begin my stopwatch and observe the gas syringe. Every 10 seconds I shall record how much oxygen has been given off of the solution and delivered to the gas syringe, as the syringe reaches its capacity I will lift the cork off of the top of the flask and push the syringe back to its original position then replace the cork. This will release the recorded oxygen and allow the experiment to continue without hassle. After conducting the experiment for each desired concentration, I shall how a comprehensive set of results and be able to draw up graphs and my conclusions. My range will be 0 to 300 seconds to ensure the Hydrogen Peroxide will be completely decomposed. However, if the gaseous release stabilizes and stops, I shall end the experiment, as the Hydrogen Peroxide will be decomposed.
The main risk, which scientists carrying out this experiment would experience, is the corrosiveness and harmfulness of the Hydrogen Peroxide. It blisters the skin and can be poisonous. This hazard can be overcome by handling the compound with care, wearing protection i.e. gloves and eye protection e.g. goggles.
Another risk is the hazard glass can pose when not handled and used correctly. The gas syringe can pop out causing a danger to the scientist conducting the experiment. This minor hazard can be overcome by handling all glassware with care and full attention.
Due to the experiment only taking a short duration of time to complete, most variables are ineffective. Categorical, Continuous and discrete variables will all be at a constant throughout the practical ensuring a fair test. The Independent and Dependant variables shall be calculated, controlled and recorded by the scientists performing the experiment, this shall also ensure a fair test.
To ensure fair testing measuring cylinders and spatulas are used to make sure that the exact same amount of each substance is used for each experiment.
Whether it be just one scientist conducting the experiment, or three, the same set of eyes and actions shall carry out the same job in each experiment to ensure fair testing.
Conclusion
- From my research I have discovered the formula: -
Rate of Reaction = volume of oxygen given off
Time taken to complete
Experiment
This formula enables me to calculate the rate of reaction for each concentration: -
20% = 377.5 ÷ 240 = 1.57 cm²/s
16% = 200 ÷ 240 = 0.83 cm²/s
12% = 296 ÷ 240 = 1.12 cm²/s
10% = 521 ÷ 240 = 2.17 cm²/s
8% = 246.5 ÷ 240 = 1.025 cm²/s
4% = 139 ÷ 240 = 0.58 cm²/s
- From my research and roughly displayed in my results I can conclude that as the Concentration of the Hydrogen Peroxide increases the rate of reaction increases and the oxygen is given off quicker. This is because when the concentration is higher, the Hydrogen Peroxide contains more tightly packed particles therefore, increasing the chance of a successful collision and speeding up the rate of reaction.
- My results do not exactly correlate with my hypothesis; this may be due to many factors affecting the experiment and the accuracy of the concentrations of the Hydrogen Peroxide. However, from my extensive research I have discovered that when in the perfect environment and conditions for the experiment and Hydrogen Peroxide, the results should be the same as to what I had predicted; as the concentration of the Hydrogen Peroxide increases the rate of reaction does as well.
Accuracy
The experiment we conducted in class was not very accurate due to a number of reasons: -
- The freshness of the Hydrogen Peroxide may have varied throughout the experiment. Due to the school funds, the school cannot produce Hydrogen Peroxide for each experiment; therefore it is stored in the science department for duration of time. Depending on the length of the storage the Hydrogen Peroxide may become weaker due to it decomposing on its own, especially if it comes into contact with sunlight. This problem could be overcome with more money to produce more amounts of Hydrogen Peroxide.
- The purity of the Hydrogen Peroxide may have also varied throughout the experiment because the whole class was taken the Hydrogen Peroxide from the same container and contamination was a possibility, this would alter the accuracy of the experiment dramatically as the Hydrogen Peroxide may have already started to decompose. This problem could be overcome with more money to produce more amounts of Hydrogen Peroxide so everyone could have a beaker-full each. Therefore, reducing the chance of contamination.
- The apparatus used was not very accurate, and in the method there was a high risk of inaccuracy. For example, the gas syringe used was only to 1 decimal place causing an element of inaccuracy, and the method to reset the syringe during the experiment would almost definitely cause an inaccuracy. The scientist conducting the experiment would take the cork off of the flask containing decomposing Hydrogen Peroxide and reset the syringe whilst releasing excess oxygen. This method would bring an inaccuracy because too much oxygen may be released when resetting the syringe, therefore causing an inaccuracy. This problem could be overcome by having larger and more accurate gas syringes or with more money having a computer monitored gas release system for the oxygen given off in the experiment.
Strange results
We had a strange result in our experiment containing the 10% concentration Hydrogen Peroxide. It decomposed at a fairly steady rate then jumped dramatically about 230cm² of Oxygen in 40 seconds. This sample of Hydrogen Peroxide also gave off 530cm² of Oxygen. I believe this was due to two things. The dramatic jump was due to there being particles of water vapour in between the gas syringe, and therefore reducing the movement of the syringe until it popped out dramatically increasing the amount of Oxygen given off. The abnormal amount of Oxygen given off was due to the freshness of the Hydrogen Peroxide as it had just been made up by one of the laboratory technicians at school, therefore making it more reactive as it had not had anytime to decompose itself in anyway.
I will modify and expand the original experiment in a number of ways. Firstly I must decide what I’m going to investigate.
I am going to investigate how temperature affects the decomposition of Hydrogen Peroxide.
Method to investigate how temperature affects the decomposition of Hydrogen Peroxide: -
- Pour 10ml Hydrogen Peroxide into a test tube.
- Place the test tube into a water bath at a certain temperature and begin the stopwatch.
- After 3 minutes in the water bath, withdraw the test tube and re-measure the Hydrogen Peroxide left. Record the amount left in the test tube.
- Carry out the experiment for temperature ranging from 10ºC to 90ºC. Don’t range the temperatures near the boiling and freezing points of water (100ºC and 0ºC), as the state of the Hydrogen Peroxide will affect the rate of reaction.
- After recording the set of results, place them onto a table and graph from analysis and observation. Enabling an investigation into how temperature affects the decomposition of Hydrogen Peroxide.
- Encarta Encyclopaedia 1998 Version CD – ROM.
- Britannia Encyclopaedia 2002 Version CD – ROM.
- Multimedia Science Software
- CGC Chemistry GCSE Revision Book.
