- Size of solid particles. If you break up a solid into smaller pieces you increase the surface area. The result of this is that there is more area for collisions to take place.
- If a catalyst is added.
In this investigation the reactants are Calcium Carbonate chips (Marble Chips) and Hydrochloric Acid. My investigation is based on the collision theory. This theory states that the more collisions between the reacting particles, the quicker the rate of reaction.
I obtained this theory from the ‘CGP GCSE Chemistry’ higher-level revision guide’.
Prediction
I predict that the smaller the marble chips, the faster the reaction. This is based on the theory that the size of particles affects the rate of reaction. This means that there will be more carbon dioxide evolved by the smaller chips. I predict that the shape of the graph will be a curve shown in the diagram below.
Preliminary Work
To determine a suitable concentration of hydrochloric acid and marble chips, I carried some preliminary work. I carried out the experiment with a number of different concentrations of hydrochloric acid and how long to time the reaction and how to measure the possible products.
2HCl (l) + CaCO3 (s) CaCl2 (l) + H2O (l) + CO2 (g)
This is the chemical symbol equation for the experiment. Using this I came to the conclusion that the Carbon Dioxide was the best product to measure and that a gas syringe was the best way to measure it.
I chose to use commercially prepared concentrations of a) 0.5 Molar b) 1 Molar and c) 2 Molar for the preliminary experiment.
I decided that a 2 Molar concentration and 1.5 grams of each size marble chip were suitable to use in the experiment. The size of the marble chips, were categorized into three groups: small, medium and large. The amount of carbon dioxide evolved was measured every 10 seconds for 100 seconds. So that we could calculate the average from our results, it was decided that the experiment should be conducted five times for reliability.
Method
We set up the apparatus as in the diagram below.
The apparatus was set up in this arrangement so that we could measure the carbon dioxide evolved precisely. The concentrations of the reactants were kept the same as was the temperature, to ensure a fair test. We did not add any sort of catalyst to make sure that the rate of reaction was not altered by any other variable that the size of the marble chips, which was the only variable that was changed. As a safety precaution everyone wore goggles for the duration of the experiment.
Results
The results from the investigation are shown in the table below
A Graph To Show and Analyze The Results From The Investigation
Conclusion
The results showed that the smaller chips reacted the fastest. This supports my prediction, but the medium chips didn’t react as well as the larger chips, which is unusual because the medium chips have a larger surface area. The graph however was unlike my prediction, the reason for this is probably because we did not record enough results. I think if we had recorded more then the graph would have curved as the carbon dioxide evolved depleted over increased time.
Evaluation
The results were generally very accurate, however there was a set of anomalous results.
These results seem anomalous, as they are nearly double
the other two sets. This could have been due to the gas syringe slipping or a fault timing the experiment
If I were to do the investigation again I would take lots more readings of the carbon dioxide evolved to get a better set of results and to get a different graph. I would also take the readings at smaller intervals, perhaps as five seconds instead of twenty to get more accurate results and a better graph. If I really wanted to get a good set of results I could gather the results from everyone else’s investigation and compare them with mine providing that the apparatus and variable were the same.
I think the investigation was accurate but would have been better if a more precise gas syringe with a smaller scale was available. Finally I would use a more advanced timing system.
The investigation was not very reliable as we got a whole set of anomalous results. This was due to a fault with the gas syringe. If I were to do the investigation again I would make sure that the syringe was well lubricated every time I did the experiment to avoid repeating the same fault. I would also use a computer controlled timing system, as there was room for human error in this investigation.
To develop the investigation further I would change the following variables to see what effect they have on the rate of reaction:
1) Change the temperature of the reactants
2) Change the concentration of the hydrochloric acid
3) Add a catalyst
4) Agitate the reactants to see what affect it had on the rate of reaction
