- Catalysts: a catalyst is a substance which increases the rate of a chemical reaction, without being used up in the process. It can be used more than once to increase the rate of conversion of reactants into products. A catalyst lowers the amount of energy needed for a successful collision- so more collisions will be successful and the reaction will be faster. Also it provides a surface for the molecules to attach to, thereby increasing their chances of bumping into each other. Catalysts are specialized so different reactions need different catalysts.
Prediction:
I shall be measuring how the change in the rates of reaction changes when the concentration of acid is changed. This change in concentration will affect the rate of reaction because when acid is diluted there is more space for the particles to move so fewer collisions take place. To make these experiments fair tests, I shall make sure that I measure all reactants and make sure the temperature of the liquid are the same. I shall take great care to make sure that no catalysts are added. I shall also make sure that I use hydrochloric acid taken from the same source to make sure it is as similar as possible but I will be changing the concentration of the liquid but diluting it with various amounts of water. I will be using calcium carbonate marble chips and hydrochloric acid to measure the rates of reaction and I will change the ratio of water: acid to change the concentration. I chose to do preliminary experiments to investigate the best amount of reactants to use in my experiments. I did 5 preliminary experiments and they all came out with various results. I came to the conclusion that 1g medium sized marble chips and 10 ml of liquid gave the best results. After doing the preliminary experiments I think the best result was the experiment that I did last. So I have chosen to use those variables in my final experiment. I think that when I perform my final experiment, I shall receive similar results to my preliminary experiment.
To find the best possible outcome, I will repeat each test 3 times and will have 6 differently concentrated acid amounts. The amount of liquid will be the same at all times but the ratio of water and acid will change. I will record each reading at 20 second intervals to reduce an excess of results.
Safety: To make sure the experiment is carried out safely, I will wear protective goggles, I shall tie my hair back, wear an overall. I shall also not sit down by the equipment while the experiment is in progress because if anything gets knocked over, I would have a delayed reaction and it would take me longer to get out of the way.
Dilute hydrochloric acid+ calcium carbonate calcium chloride + carbon dioxide + water.
2HCl(aq) + CaCO3(s) CaCl2(aq) + CO2(g) + H2O(l)
Diagram of equipment:
I will use a gas syringe to measure the amount of gas given off, a conical flask to hold the reactants, a measuring cylinder to measure the acid, a set of scales to measure the marble chips and a clamp stand to hold the gas syringe. I will also have a rubber tube and bung to transport the gas into the syringe.
Results of Rates of Reaction Experiments:
Throughout the experiments, I used 2 molar hydrochloric acid and 1gram of medium sized marble chips. This was to keep the tests fair. I varied the concentration of he hydrochloric acid by combining different amounts of water with different amounts of hydrochloric acid to decrease the molarity but keep the same amount of liquid in the equation.
Conclusion:
From analysis of the results I have recorded, I have come to the conclusion that the rate of reaction gets slower when the concentration of acid is weakened. This is proven by the graphs showing my data. This proves my prediction about the particle theory. I stated that when concentration was increased, the rate of reaction increased because the amount of particles increases but the surface area stays the same so the particles are closer together and therefore have more collisions.
Evaluation: the experiment I carried out went according to plan but the results I obtained weren’t what was predicted or expected. I have obtained sufficient amounts of results but it still doesn’t help me come to a conclusion. I feel that I controlled the experiment well but I don’t quite understand why the results turned out like they did. The only resemblance I can see between the results is that all the results travel upwards except for the averaged results for 90%.looking at the averaged results, the results are quite ‘jumbled up’ because 30% is higher than 50% and 90% and 70% are higher than 100%.
From these results, it is unclear to see whether or not the rates of reaction changes when concentration is changed.
The experiments were very suitable to test whether concentration changes the time taken for a reaction to occur between calcium carbonate and hydrochloric acid. The results given were hard to decipher because some reactions were quicker than others and lasted longer than others but that was because I used the averaged results to make the averaged results to make the graph of all results. I think that when I averaged the results, there was one or two anomalies singly which changed the average for each result. This also altered the 90% result because it was impossible for the results to go down but they did at 90%.
I chose a sufficient range of variables to test because I don’t think it was necessary to do any variables less that 30% because it would have been extremely slow with not much reaction taking place and that is evident from the other results.
The results for 50%, 80% and 100% were anomalous because 100% was below 90% and 70% while 50% was the lowest result, lower than 30% and also, 80% was lower than 80%. But it could also be seen as 30%, 70%, and 100% being anomalous because 30% is higher than 50%, 70% is higher than 80% and 100% and 100% is lower than 70% and 90%. So in comparison to reach a final result, it is impossible to define which result/results were anomalous except I came to the conclusion that 100% is anomalous.
Looking back on when I performed the experiments, I have realised that I obtained the results of each variable on different days so I came to the conclusion that we may have used different equipment each day which caused the range in results. I am quite sure that it was the gas syringe that was faulty but that is the only reasonable explanation I can think of.
I received plenty of results to come to a conclusion and if I could do it again, I would do more variables and test each variable one or two more times so that I can pick out the best three for each variable. That would give me a more consistent result.
