Apparatus
*Safety glasses*
Balance
Medium sized Calcium Carbonate
2 m of hydrochloric acid
Flask (with a bung and a glass tube)
Bowl full of water
100 cm³ measuring cylinder
50 cm³ measuring cylinder
Stand, Clamp and Boss
Stop Watch
Supply of water
To begin my investigation, I will put on my safety glasses for safety and use a balance to measure 1 gram of medium sized calcium carbonate. I will need a flask with a bung so the released carbon dioxide does not disperse into the air instead of going down the tube into the 100 cm³ measuring cylinder.
After setting up the apparatus like in the diagram, I will put the 100 cm³ measuring cylinder into the bowel full of water, thus filling it up with water and getting rid of any air bubbles. Then I will hold it upright using a stand, clamp and boss, and put the tube from the flask pointing up the 100 cm³ measuring cylinder. After this, I will put 1 gram of medium sized calcium carbonate into the flask and then put the particular concentration of hydrochloric acid (which I have previously worked out using the 50 cm³ measuring cylinder) into the flask, quickly replacing the bung and immediately starting the stopwatch. Then, every 10 seconds, I will record how much the level of water in the measuring cylinder has decreased.
My preliminary results are as follows:
From this experiment, I found out that as the volume of acid increases and the volume of water decreases the rate of reaction is a lot faster and therefore, more carbon dioxide is given off in the 1 minute 40 than a lower concentration. I also found out that I could probably do three different concentrations in 50 minutes, (allowing ten minutes for setting up and clearing away). By working out how long experiments will take, my actual experiments will be a lot more organised and I have a goal to work towards.
So, from my preliminary experiment I can predict that this experiment will take approximately 167 minutes. I also know that it is most likely true to collision theory and this means that as the concentration of acid increases, the rate of reaction will increase also.
Experimental Plan
From my preliminary experiment, I can now construct a more detailed plan of my experiment.
Apparatus
*Safety glasses*
Balance
Medium sized Calcium Carbonate
2 m of hydrochloric acid
Flask (with a bung and a glass tube)
Bowl full of water
100 cm³ measuring cylinder
2 x 50 cm³ measuring cylinder
Stand, Clamp and Boss
Stop Watch
Supply of water
I will begin by setting up the apparatus as done in the preliminary experiment. I will use a 50 cm³ measuring cylinder for measuring the concentrations of acid because I only need 50 cm³ of both acid and water overall, each time and by using the smallest possible measuring cylinder, I can achieve much more accurate results. I will use a 100 cm³ measuring cylinder for measuring the amount of carbon dioxide because in the preliminary experiment, the highest it got to was 75, which is less than 100, so therefore 100 cm³ measuring cylinder is ideal for this experiment for the same reasons as the 50 cm³ was used to measure the concentrations.
After setting up the apparatus, I will measure 1 gram of medium sized calcium carbonate (to two significant figures) on a piece of paper on the balance, the paper is there so the calcium carbonate can easily be transferred without losing some of the calcium carbonate. The surface area of the pieces of calcium carbonate must all be about the same each time so the experiment is fair. If the pieces of calcium carbonate are smaller than medium sized then there will be more area exposed and therefore able to collide and react, and therefore it will give off more carbon dioxide. Whereas if the pieces are too big there wont be so much area exposed and therefore to react with so the calcium carbonate will not give off as much carbon dioxide as it should.
After measuring the calcium carbonate accurately I will pour the pieces into the flask and then take one of the 50 cm³ measuring cylinders and carefully measure the 2 m hydrochloric acid, then I take the other 50 cm³ measuring cylinders and measure the water. I wont use the same 50 cm³ measuring cylinder and measure both the water and acid in it at the same time because if the water goes wrong and I have already measured the acid in it, then I would have to start the measuring all over again.
I will then pour the water into the measuring cylinder with the acid in and pour this into the flask, when I replace the bung I immediately start the stopwatch when the first bubble of carbon dioxide appears from the tube coming from the flask. Then, every 10 seconds I will take down the measurement on the 100 cm³ measuring cylinder. However, I will take down the measurement on one second before 10 so I can allow time for working out the measurement of carbon dioxide.
I will take a total of five measurements then repeat them so it is easier to spot anomalies. I will take measurements for a concentration of completely acid (2 M), this will act as a control for the experiment and will show that my results are reliable, by showing that the water does have an effect on the amount of carbon dioxide produced and therefore the rate of reaction. 1.75 M (43.75 cm³ of acid and 6.25 cm³ water), 1.5 M (37.5 cm³ of acid and 12.5 cm³ of water), 1 M (25 cm³of acid and water) and 0.5 M (12.5 cm³ of acid and 37.5 cm³ of water). I feel that these measurements as well as being relatively easy to work out cover a wide range of measurements and from them I will probably be able to make a valid conclusion.
My prediction for this experiment is based on the preliminary results, I think that generally, as the concentration increases the rate of reaction becomes slower and therefore will produce less carbon dioxide in the 2 minutes, 20 seconds than a lower concentration. I think this because in the collision theory, the more acid to react with the calcium carbonate the more likely a successful collision will be, so
The more acid the more collisions the more reactions the more carbon dioxide produced the bigger the rate of reaction.
Results
You work out the rate of reaction by volume divided by time.
Conclusion
The averages of the two experiments I did for each concentration show that my prediction was correct. As you add more and more water to the hydrochloric acid, the rate of reaction lessens. This is because it is the hydrochloric acid and the calcium carbonate, which react by collision theory. By making the acid less concentrated by adding the water, it means that there are fewer acid particles to collide and therefore react with the calcium carbonate, by making the solution more concentrated; there is a much bigger chance of a successful collision.
Evaluation
My results in places were quite anomalous, however, averages of the two results and then averages of the rates for each one, caused my results to look reasonably successful and accurate. However, looking at both of my graphs it is clear that the results I received from the 2 M concentration were faulty. If you compare the line of best fit of the 2 M concentration to the others, you can see that in the averages of my results graph, the gradient is incredibly steep compared to the others and in my average rates of reaction graph, it shows the 2M concentration is incredibly faster than the other concentrations and though it is the highest concentration, the results should not be that high compared to the others.
If you look at the repeats of my experiments, you can see that throughout my experiment, the repeats have been pretty similar to the first set recorded. The only exception being the concentration of 1 M, where peculiarly one set of results ended at 15 and the other at 31. Perhaps what happened here was a case of human error, I think the most likely explanation was that I used the wrong surface area of calcium carbonate, as this would be very easy to do accidentally.
In my averages of results graph, there are no particular anomalies, all the points follow pretty much the same line, the only problem is that the 2 M concentration line of best fit is an anomaly in itself, as I have previously mentioned. However, in the average rates of reaction graph, there are quite a few anomalies, these I have circled on the graph. These anomalous results are all at the beginning of the experiment and therefore are probably due to human error by misreading the volume on the measuring cylinder, or they could be due to not putting the bung in the flask quick enough.
In my method, I did find one extreme flaw, when I used my 100 cm³ measuring cylinder, I thought, with evidence from my preliminary experiment, that I would not need a bigger one because my results would not go past 100 cm³. However, as you can see from my results in the 2 M experiment, it did go beyond 100 cm³ and this made it incredibly hard to measure the volume of carbon dioxide after this point. As it so happens the 2 M experiment was flawed due to human error anyway but in future I will use a 250 cm³ measuring cylinder just in case.
I could extend the experiment to provide further evidence for my conclusion by investigating the separate surface areas of calcium carbonate. If my conclusion is true, then from these experiments I should conclude that as the surface area increases, the rate of reaction is much faster. This is again due to collision theory. Because the acid particles can only collide with the outer calcium carbonate molecules, if there is a big block of calcium carbonate, the acid particles can only collide with the outer layers. However, if the calcium carbonate were powdered, many more molecules would be exposed, so the acid particles have a much greater chance of successful collision and so the rate of reaction is faster.
