Chemistry Investigation catalysts.

GCSE Catalyst Investigation Page

Chemistry Investigation catalysts

Aim

Prediction

I predict the higher the amount of catalyst used the higher the rate of reaction (ROR). This is because a catalyst speeds up a reaction; so the higher the amount of catalyst used the higher the ROR. The ROR can be measured by the amount of oxygen given off by the reaction. My preliminary work also points out that the higher the amount of catalyst used the more vigorous the reaction, I think this is because. The hydrogen peroxide is slowly breaking down, the catalyst works like an enzyme, it speeds a reaction up without taking part in it.

I predict that this reaction will be sped up by the catalyst:

2H202 → 2H2O+O2

The reaction I predict will take place:

2H202 → 2H2O+O2

MaO2

A Catalyst is a substance that alters the rate of a chemical reaction without itself undergoing any chemical change.

If a reaction has more catalyst present, the catalyst (Manganese Oxide), stands more chance of colliding with a hydrogen peroxide particle, thus creating a greater reaction rate. If there is less catalyst then, the catalyst will take longer to collide with the same amount of hydrogen peroxide and make it react. The diagram bellow illustrates this:

Manganese oxide (the catalyst) Hydrogen peroxide

My preliminary work seems to agree with this conclusion so far:

In my preliminary work I tried different amounts off catalyst with a 50% hydrogen peroxide solution and this is what I found:

From this I have chosen range of catalyst to use; 0.02g- 0.1g

Variable

I will only change one variable. I will change the amount of catalyst used. From my preliminary work I can predict that a good range of catalyst to use is 0.02g to 0.1g. I will not change the strength of the hydrogen peroxide used, I will use a 50% solution because it slows the reaction down, and so I can take more precise readings. I will keep the temperature the same (room temperature 20°C). I have not chosen to change this variable because; it would be harder to get a precise temperature than measuring a different amount of catalyst each time. Therefore, there would be three things that could potentially make my results inaccurate. If I use room temperature as my variable and check the temperature is exactly 20 will be more accurate than heating the hydrogen peroxide to 40. By using the amount of catalyst as my variable I can minimize my error margin. If I use catalyst as my variable I will have to check the temperature to make sure it’s 20.

I have chosen to use the amount of catalyst used as my variable. I will use these amounts of manganese oxide: 0.02g, 0.04g, 0.06g, 0.08g, and 0.10g.

To make it a fair test, I will keep the following variables the same: temperature, concentration of hydrogen peroxide, amount of hydrogen peroxide used
I will change this variable: Manganese Oxide

Fair test

I will only change one variable as changing two variables could have two effects on the ROR. I will do repeats for all my tests. I will make sure that each reaction happens at the same initial ...

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I have chosen to use the amount of catalyst used as my variable. I will use these amounts of manganese oxide: 0.02g, 0.04g, 0.06g, 0.08g, and 0.10g.

To make it a fair test, I will keep the following variables the same: temperature, concentration of hydrogen peroxide, amount of hydrogen peroxide used
I will change this variable: Manganese Oxide

Fair test

I will only change one variable as changing two variables could have two effects on the ROR. I will do repeats for all my tests. I will make sure that each reaction happens at the same initial temperature, by using a thermometer. I will be very careful when measuring the amount of hydrogen peroxide and the amount of catalyst (Manganese Oxide). When using a measuring cylinder, I will remember to read the bottom of the meniscus. If one of my results seems unusual, I will make sure I repeat it.

Safety:

I will wear safety goggles
I will be careful with the hydrogen peroxide, as it can be harmful as it blisters the skin.
I will be careful with all lab equipment, especially glass equipment as it could shatter.

Equipment & chemicals needed:

Burette
Delivery Tube
Conical Flask
Jack/pile of books etc
Water container
Distilled water
Water
Hydrogen peroxide
Manganese Oxide
Cork/bung
goggles

Method

I will set up the equipment as shown above. I will make a 50% solution of hydrogen peroxide by mixing 50cm3 of hydrogen peroxide and 50cm3 water. I will use 25cm3 of hydrogen peroxide solution with each test. The amount of catalyst I will use in my tests: 0.02g, 0.04g, 0.06g, 0.08g, and 0.10g. I will take readings of the amount of water displaced from the burette, as this is the amount of oxygen released from the reaction, which mirrors the reaction rate (ROR). I will take readings every 10 seconds of the amount of water displaced from the burette. so I can see how the ROR changes throughout the reaction. I will repeat each test twice.

Results:

Table recording the amount of gas (oxygen) given off from the reaction at different time intervals:

1st Set of Results:

2nd Set; Repeats

Table showing average amount of time each reaction takes two displace 25cm3 of water

Conclusion:

My results show that the higher the amount of catalyst used the higher the reaction rate.

Manganese oxide (the catalyst) Hydrogen peroxide

I can conclude that this is because a catalyst speeds up a reaction, and Manganese Oxide is a catalyst, so the higher the amount of Manganese Oxide used the higher the ROR. The hydrogen peroxide is slowly reacting (breaking down), and the catalyst works like an enzyme speeding this reaction up without actually taking place in it. The hydrogen peroxide is slowly breaking up into its chemical ingredients, (hydrogen and oxygen) because the bond between the hydrogen and oxygen particles is not very strong. The bond between the two oxygen atoms and the two hydrogen atoms is stronger. So to summarize I can say that the oxygen and hydrogen particles prefer to be separate.

The reaction that took place was:

2H202 → 2H2O+O2

MaO2

If a reaction has more catalyst present, the catalyst (Manganese Oxide) and the hydrogen peroxide particles stand more chance of colliding with each other, thus a greater reaction rate. If there is less catalyst then, the catalyst will take longer to collide with all the hydrogen peroxide particles and thus the reaction time and speed increases. The diagram above illustrates this.

I can conclude that I was correct in my prediction; my results show the higher the amount of manganese oxide used, the higher the ROR.

Evaluation

I am reasonably pleased with the majority of my results. My results confirm my prediction and look reasonable constant on a graph. I have a few abnormalities, or anomalous results for example; 0.08g of catalyst does not fit in well with the line of best fit on my graph.

My results may be inaccurate for a number of reasons; the measurement of the chemicals used could have been inaccurate. For example when measuring out the 50% hydrogen peroxide solution I could have made a measuring error. It is hard to measure precise amounts of liquid because of the meniscus, which distorts the actual level of water. When measuring out the manganese oxide, I could only be accurate up to 0.00 of a gram, so I could have been experimenting with 0.04 9g instead of 0.04g,which may have made my results very inaccurate. Another thing that made my results inaccurate was when the manganese oxide was added to the hydrogen peroxide, the reaction was already being affected by the catalyst, but the bung was not added to the conical flask for a second or so, this may cause my results to be inaccurate. Another factor is that not all of the manganese oxide from the measuring dish was actually going into the hydrogen peroxide, as after it was added there was still a black mark of the measuring dish, where the manganese oxide had been. I could have made a timing error, or a reading error when noting down results.

I could have made my results more accurate in a number of ways; I could have used more precise measuring equipment; for example a weighing scales that measures up to 0.000g, this would increase the accuracy of my results greatly. I could do more repeats, as this would make my results more accurate, if I took the average of all sets of results.

Although my evidence/ results are not perfect, they are still satisfactory to support my conclusion. I set out to see how the amount of catalyst used affects the reaction, and my results show a trend. What makes me more convinced that I can support my results is that my prediction is similar to what actually happened. My results contain a few anomalies but they are still sufficient to support my conclusion. My results are not accurate enough to say; for example that it takes 32 seconds for the reaction to complete if 0.01g of catalyst is used.

I now know the affect that the amount of catalyst (manganese oxide) used has on the reaction rate off hydrogen; I could keep this variable the same and alter the strength of the hydrogen peroxide solution. I would still use the same equipment set up as before, but would use the concentration of hydrogen peroxide as my variable, instead of manganese oxide. I would use these concentrations of hydrogen peroxide: 20% 40% 60% 80% 100%, the hydrogen peroxide would be diluted with water.