- First, I will gather all of the equipment listed on the previous page.
- I will then make up my concentration of acid and put it into the conical flask.
- Next, I will fill the margarine tub between ½ and ¾ full.
- I will then fill the measuring cylinder full of water, and tip it upside down in the margarine tub, ensuring that as little air as possible gets in.
- The measuring cylinder will then be secured upright using the clamp.
- Then, I will put 5 marble chips, of roughly equal surface area, into the acid.
- I will then put the bung of the gas delivery tube into the water in the margarine tub.
- When the gas begins to bubble out of the end of the tube, I will place it under the measuring cylinder to collect the gas.
- At the same time as the previous step, I will set the stopwatch going.
- I will then, note the amount of gas collected every 10 seconds.
- I will then repeat the experiment as many times as need be, using different concentrations of acid.
Measurements to be Taken
In this investigation I will be measuring the amount and rate that carbon dioxide is produced, when marble chips (calcium carbonate) are put into hydrochloric acid of varying strengths. I am going to test each concentration 3 times to make sure that the investigation is fair, and will then work out averages, rates of production, gradients etc.
I will measure the amount of carbon dioxide in cubic centimetres, and will take measurements every 10 seconds. I will be collecting the gas using a measuring cylinder that has been upturned in a margarine tub between ½ and ¾ full of water.
Fair Tests
To make this investigation fair, I will be using the same amount of marble chips, and will ensure that they have roughly the same surface area. I will do this because if I used marble chips which had different surface areas then more acid would be able to reach the marble so more gas would be given off in less time.
I will also take measurements as soon as possible after the gas starts to comeout of the tube. This is because as the marble chips dissolve into the acid their surface area gets smaller, resulting in gas being given off slower.
I also tried to keep the temperature about the same throughout the experiment. This is because with more heat energy the particles will gain more energy, and therefore move faster. If the particles move faster, there will be more collisions and therefore the reaction will take place faster.
I also kept the time between measurements the same. If I had waited 12 seconds instead of 10 for one of the measurements, the amount of gas measured would not be a true measurement. Therefore, I used a stopwatch to measure time.
Safety
To help make this experiment safe I will wear goggles at all times during the experiment or whilst others are doing the experiment near me. This is so that if for any reason acid gets splashed at me, it will not go in my eyes. If acid did get in my eyes it could damage them.
I will also stand up whilst doing the experiment because if acid gets spilled, I will be able to get out of the way quickly so that it doesn’t get on me or my clothes. If I was sitting down it would be harder for me to stop the acid from getting onto me.
If I spill any acid onto me I will rinse the area under the tap, to get the acid off. I would need to do this because hydrochloric acid is corrosive and therefore would hurt or even damage me.
I will not run or mess about in the laboratory in case I spill acid, which would cause a safety hazard for the same reason as above.
The concentrations of acid I am using in this experiment are so weak that it doesn’t really matter too much if I do come into contact with it. I will still carry out the safety precautions however, so that there is no possible danger.
Section 2: Obtaining
Results Table
My results tables are at the end.
Section 3: Analysis
Analysis
From my results I can see that generally as the acid that I used got weaker, the less gas was produced. This is shown by the fact that with 100% concentration of acid I measured an average of 69.67cm³ of carbon dioxide, the average gradually decreases apart from at 70% where it increases, but from then onwards goes steadily down.
In the 100% concentration test, where I used 2M Hydrochloric acid, the volume of gas had increased by about 6, 10 seconds after the last measurement. With the 90% concentration test, I have decided to ignore the first set of measurements because I feel that they are not accurate. Therefore I have remade the table as follows:
I can see from this that the amount of gas measured goes up by about 4 cm³ every 10 seconds.
During the 80% test the gas produced increases by about 3cm³ every 10 seconds.
In the 70% concentration test the gas produced increases by about 4cm³ every 10 seconds, this is strange because, logically it should increase by less than the 80% concentration test. By surveying the other results and the patterns that have emerged from them I would estimate that it should have increased by 2cm³ every 10 seconds instead of by 4cm³. I think that this has happened because the marble chips were probably larger. This is explained in more detail under the section entitled “Anomalous Results”
In the rest of the tests the rate that carbon dioxide is given off, seems to level off at about 3-4cm³ every 10 seconds.
Conclusion
From this investigation I have learned that if an acid is concentrated it is more reactive. Being more reactive means that for instance, in this experiment, more carbon dioxide is produced and at a faster rate. If the acid were less reactive the reaction would take place slower, therefore less carbon dioxide would be produced overall, and at a slower rate.
Proving the Prediction
On the whole, my prediction was more or less right. As the acid got weaker, the amount of gas produced, decreased, apart from at the 70% concentration, where it instantaneously increased. This was probably caused by using marble chips that had a larger surface area to the ones I had been using before. This was due to the fact that I had to slightly adjust the size of the marble chips I was using, as there were no more marble chips that were the same size as the ones that I had been using previously. To get avoid this problem I could have used specially prepared marble chips, that had a fixed surface area, such as 1cm³ cubes. This would have increased accuracy, but would also have increased the cost of the investigation by quite a lot.
I also predicted though that there would twice as much gas produced with 100% concentration than there would have been with 50% concentration. This was nearly right as the average volume of gas produced with 100% concentration was 69.67cm³ and the volume of gas produced with 50% concentration was only 29.33cm³. Rounded up to the nearest whole number these work out at about 2.5 times more gas produced. I think that this is near enough to my prediction.
Section 4: Evaluation
Evaluation of Evidence
I do not think that all of my results are reliable. There seems to be major differences between some of the results, for instance the first repetition of the 90% concentration test, produced carbon dioxide at higher rate than that of the 100% concentration test. It also has a higher overall volume than the 100% concentration test and is double that of the other repetitions.
I also do not think that the 70% and 60% results are reliable because they both have a larger overall volume of gas produced than the 80% test.
Anomalous Results
During this investigation I did get some strange results. In the first version of the 90% concentration, overall more carbon dioxide was produced than in any of the 100% concentrations. This should not have happened because the acid was weaker so the reaction should have taken longer. The reaction took longer in all of the other repetitions, so why did it take longer in this case?
There are several reasons why this could have happened. These are: That the acid could have been stronger; or the surface area of the marble chips could have been bigger. The first of these is hard to justify, but could have happened if by accident more acid than was supposed to be put in was put in. This could have happened but it is impossible that the acid was more than 100% concentration, which it would have needed to be in order to produce more gas than the 100% concentration experiment. This only leaves the second explanation: That the surface area of the chips was larger. This could have been for any reason, such as: The marble chips were larger than in the other tests; more marble chips than should have been put in, were put in; or maybe that one of the marble chips had a crack in. I would guess that more marble chips were put in, although it could have been because of any of the other reasons. From the fact that almost twice as much gas was collected in the first repetition, I would say that either 2 lots of marble chips were put in by accident, or the marble chips from the last test (the 3rd repetition of the 100% concentration test) were still in the conical flask.
To stop this happening again, if I did another investigation, would be to always check that the experiment has been set up correctly with the right quantities and concentrations of everything.
Also the average volumes of gas with the 70%, and 60% concentrations of acid, are higher than that of the 80% concentration test. This should not have happened because the acid should have been weaker. This was probably caused by using marble chips that had a larger surface area to the ones I had been using before. This meant that there was more marble for the acid to react with, and therefore produced more gas.
In order to stop this happening, if I did the experiment again I could use marble chips which all have exactly the same surface area. This would increase accuracy but unfortunately make the investigation to expensive to carry out, as the marble chips would probably have to be specially prepared.
Evaluation of Method
I think that my method worked quite well, although next time I would use marble chips with a set surface area. This would improve the accuracy of the investigation. Also I would check to make sure that the experiment was set up properly with the right amounts of the chemicals and substances that I was using. I would do this to ensure my results were accurate.
Is the Conclusion Valid?
I think that my conclusion is valid because my colleagues all had pretty much the same sort of results.
Results
All of the units in the following tables are in cm³, apart from the units in the “Time” columns which are in seconds
