An Investigation of the weathering of limestone.
An Investigation of the weathering of limestone.
Purpose of experiment: To investigate if the concentration of acid affects the rate of reaction of the weathering of limestone.
Plan: We will situate hydrochloric acid with limestone (calcium carbonate) and we will adjust the concentration of the acid to determine if the dilution of the acid affects the speed of the reaction of the weathering of the limestone.
Pre trial run: In the pre trial run we did a quick experiment to see if there were any problems that we needed to solve. We discovered that the dilute acid was going incredible slowly and we would not have enough time to do the experiment a number of times so we could get a good average in our final results. We established that if we constantly swirled the conical flask that the rate of the reaction would be much faster. We will do this in our concluding experiment but for all the different concentrations of acid. We also uncovered that we need to measure in seconds and not minutes and seconds as to make the results easier to understand and to comprehend the rate of reaction. I found the pre trial run essential to the experiment, as we could find out the measurements we will use, and to deliberate with another group so we can set our results together so we can be able to get a enhanced average, which will lead to a more precise rate of reaction. I will explain our measurements in a later paragraph.
Safety: In the experiment I will be as safe as possible. I will tie back my hair to keep it from falling into the experiment, wear my overall to protect my clothes from the acid and wear goggles over my eyes to protect them, also from the dangerous acid. I will make sure that stools and bags are carefully stowed away so that we do not trip over them. I will also make sure that the experiment is in the centre of the table so nothing will be able to easily get broken or fall on my toes! I hopefully will not get acid on my skin but if I did I would wash it off immediately and if there was a spillage of acid I would ensure that it was quickly wiped clean and we will watch very carefully what we are doing at all times.
Fair test: I will try to make my experiment fair by only changing one variable. I will keep the amount of limestone the same at five grams and the size of the limestone chips about similar. The total amount of liquid will always stay the same at 100ml. The equipment will be the same as possible but because we are performing the experiment over two days this will be difficult, but we will still use the same kind of equipment. We will use the same kind of acid, being hydrochloric acid. We will try to keep the temperature of the acid the same, at room temperature, but the temperature of the room could differ depending on the weather, but unfortunately there is nothing that can be done to change the weather. All the time we will start the stopwatch from the first bubble and stop it when we get to 25mils of carbon dioxide in the measuring cylinder. We will also use the same units of time each time and measure time to the nearest tenth of a second, and we will also weigh the limestone to the nearest tenth of a gram. Hopefully our experiment will be fair and we will try our hardest to make sure that it is.
Changes: The only aspect we will change in our experiment is the concentration of the hydrochloric acid so we will be able to get our results and come to a conclusion.
Measurements and Trials: In our experiments we will change the concentration of the acid five times. This way we will be able to get a clear picture of how the concentration of the acid affects the rate of reaction on the limestone. Our five measurements will be 20% acid and 80% water, 40% acid and 60% water, 60% acid and 40% water, 80% acid and ...
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Changes: The only aspect we will change in our experiment is the concentration of the hydrochloric acid so we will be able to get our results and come to a conclusion.
Measurements and Trials: In our experiments we will change the concentration of the acid five times. This way we will be able to get a clear picture of how the concentration of the acid affects the rate of reaction on the limestone. Our five measurements will be 20% acid and 80% water, 40% acid and 60% water, 60% acid and 40% water, 80% acid and 20% water and 100% pure acid. We will make two trials at each measurement of the concentration of acid but finally we will have four sets of results as we are going to put our results together with another groups who are using the exactly same experiment as us so we will all be able to keep to a fair test. Then with four sets of results we will be able to get a high-quality average, excluding anomalous results. With only one or two sets of results we will not get a good average and we will not be able to tell if a result is anomalous.
Prediction: I predict that the rate of reaction will be faster in the pure acid than the dilute acid. In order for a reaction to take place the reactive particles must collide with each other with enough energy. The concentration of acid affects this because in a dilute acid there are not so many reacting acid particles; only twenty % of all the liquid particles are acid. This means there is not much of a chance of a reactive acid particle colliding with a limestone reactive particle. When all the liquid is acid only reacting acid particles can collide with the limestone particles so there are more successful collisions occurring. The more successful collisions there are, the faster the reaction. The 100% acid will go five times as fast as the trial with 20% acid because there are five times more reacting particles of acid for the limestone particles to collide successfully with. This is not quite accurate because the reaction slows down over time. In the dilute acid it has time to slow down so it has a greater impact on the rate of reaction. At the start of the reaction there are little reacting acid particles, but they get used up during the reaction so there are fewer limestone particles and fewer reacting acid particles and consequently the reaction slows down. In the concentrated acid there are more reactive particles to begin with but as they are used in the reaction there are less. But there are still quite a few reacting particles left so the rate of reaction won't be greatly affected.
Quantitive diagram
Apparatus: In the experiment I will use a balance to weigh out the limestone accurately with a spatula from a beaker. I will use a 100ml cylinder to measure out the acid and the water. I will also use a conical flask for the reaction to take place, a delivery tube to carry the carbon dioxide to the 75ml-measuring cylinder to measure the gas with. We will also use a trough full off water that the measuring cylinder was sitting in. Finally we will use a stopwatch to time the experiment and a calculator to work out the rate of the reaction-taking place.
Displaying results: This is how I will show my results.
Time to measure 25mils of carbon dioxide gas C02
Concentration of acid
Trial
Trail
2
Trail
3
Trail
4
Aver-
age
Rate
ml/sec
20% acid
20
mils
80
mils
40% acid
40
mils
60
mils
60% acid
60
mils
40 mils
80% acid
80
mils
20
mils
00% acid
00
mils
0
mils
Precision: I hope my results will be fairly accurate. When we are measuring the weight of the limestone to five grams we will measure to the nearest tenth of a gram to ensure accuracy. We cannot measure the volume of the acid and water as precisely as we would like to, we can just measure it in the measuring cylinder and judge the volume with our eye to see it we have got approximately 100ml of liquid. The time we will measure in seconds and not minutes and seconds so we can easily work out the rate of reaction. We will measure the time to the nearest hundredth of a second if the stopwatch goes into that time, if not we will go as precisely as we can to make it a fair test. We will try to make everything as precise as possible but unfortunately there will probably be occasional human error involved.
Secondary Research: I searched the Internet and Encarta for research about acid rain, where the most is, and it's effects on limestone. In reference one from www.zephryus.demon.co.uk/geograghy/resources/environ/acis.html it states that acid rain has a lower pH number than vinegar making it so acidic that some things can't survive. Buildings are damaged, especially ones made from limestone. The acid eats away at the buildings and they can't survive when the acid comes into contact with it. Reference two is from the same website and explains more developed countries have now realized that acid rain can't continue as it will damage too many things and will damage the environment for us and for future generations. Reference 3 from www.doc.mmu.ac.uk/aric/eae/Acid_Rain/Older/Buildings.html includes a quote from Robert Angus Smith in 1856 who first discovered acid rain and explains that where fossils fuels are burnt to give us energy that more acid rain is present. This relates to reference 5 and 6, which I will mention later. In reference 4, which is from the same site as 3, explains that limestone is very subject to acid rain and often needs restoring. Many older British buildings have been damaged due to acidic rain because the builders didn't know the effects of acid rain on limestone or marble, which is the metamorphic type of limestone, which is a sedimentary rock. Reference 5 is from http://nadp.sws.uiue.edu/isopleths/maps2000/so4.gif it is an isopleths map, which shows the location of things. This shows the location of the sulphate concentrations in the US. It shows where the most concentrated acid rain falls, represented by the red areas. The darkest red areas are in the north-east of the US, so this must mean that according to Robert Angus Smith that there is where the most fossil fuels are being burnt, so that is where the most concentrated acid rain falls. Reference 6 is also an isopleths map but from www.soton.ac.uk/~engenvir/environment/air/acid.how.big.problem.html show it in Europe. It also explains that winds could bring clouds with acidic rainfall in to their country. Britain has a high percentage of forest damaged by acid rain but doesn't have any acidic clouds. This means that we produce nearly all of our acidic rain ourselves. References 7 and 8 from Microsoft Encarta explain all about acid rain and how it affects not just buildings but plants and animals as well. Reference 9 from www.ems.psu.edu/info/explore/acidr/effects.htm show a picture of a statue that has been affected by acid rain by only over 61years and explains if things are made from both marble and limestone what acid rain does to them. Finally reference 10 from www.epa.gov/airmarkets/acidrain/effects/materials.htlm explains that that after acid rain has come in contact with the material that the value will not be near as much.
My secondary research has explored the effects of acid rain on limestone, where the problem areas are and why they are in those locations.
Method: First of all we made sure we were all abiding to the safety rules, (all are explained in the safety paragraph.) We then set up the apparatus as shown below in the diagram. We carefully chose our equipment, which I have listed in the apparatus paragraph. We carefully chose this beforehand in our pre-trial run, so as not to waste any time. We worked well as a team and assigned ourselves to different jobs that we did for each trial. One measured accurately the volume of acid and water, one cleaned the conical flask out and prepared the measuring cylinder in the trough, making sure that it had no air bubbles, one measured the weight of the limestone chips and one mopped up the table and set the stopwatch. When everything was prepared for the actual experiment we all gathered safely around the apparatus. The limestone was already in the conical flask, and we added the acid, quickly placed the stopper on it, began to swirl the flask and started the stopwatch as soon as the bung was in place. As one person watched the time, another swirled the conical flask with the limestone and acid/water, and another watched the amount of gas carefully, whilst the other already was weighing out the next set of limestone. When the measuring cylinder was filled with 25mils of carbon dioxide gas, the stopwatch was quickly stopped and the results were recorded. We repeated this procedure until all of results were done, then we tidied away and cleaned up.
Diagram:
Results:
Time to measure 25mils of carbon dioxide gas C02
Concentration of acid
Trial
Trail
2
Trail
3
Trail
4
Aver-
age
Rate
ml/sec
20% acid
20
mils
80
mils
50.97
66.7
05.87
08.93
83.12
0.3
40% acid
40
mils
60
mils
50.33*
37.66
38.38
61.02*
38.02
0.66
60% acid
60
mils
40 mils
32.19
29.13
26.29
38.58*
29.21
0.86
80% acid
80
mils
20
mils
24.27
9.56
8.13
9.67
20.41
.22
00% acid
00
mils
0
mils
9.59
7.32
9.37
1.04
4.33
.74
Accuracy: We tried to make our results as accurate as possible. We did this by doing 4 trials so if we encountered an anomalous result we could work out which it was and not include it in our averages. Our group only did two trials but we put our results with another group who used the same measurements as we did so it was fair. I do not know if their results are accurate because we were two different groups not working together. I excluded the anomalous result from the averages because they would have given us an unfair and false average. I used the averages to work out the rate of reaction. Our readings were fairly accurate and I have mentioned what we measured to in the precision paragraph. I think our results were moderately accurate although as always they can't have been that accurate because we got some anomalous results due to human error.
Conclusion: We revealed that as the acid is more dilute the rate of reaction slows down. The higher the concentration of the acid, the faster we collected 25mils of Carbon dioxide. The faster we collected the gas, the higher the rate of reaction was. The results show this because on the graph the highest point on it was of 83.12 at 20% acid and 80% water. This is the longest it took to collect the gas. The lowest point on the graph was at 100% acid with 14.33 seconds to accumulate the gas. At 40, 60 and 80% acids, they were in between these results, giving me a curve of best fit, going down from the 20% acid where it was the highest because it took the longest time, to 100% acid which took the fastest time so gave a low point on the graph.
At 20% acid it took longest because only 20% of all the particles were reactive acid particles, so that the chance of a successful collision is quite small. Whereas in 100% acid where it only took on average 14.33 seconds to collect the gas, this is because that there was only reactive acid particles can have a collision with the limestone as it is not dilute with water.
The rate of reaction is measured in mils/sec. At the most dilute acid, which only had 20% of reactive acid particles in it so it has a slow rate of reaction, with 0.3 millimetres of gas per second. In 100% acid it's rate of reaction was 1.74 millimetres of gas per second that is the fastest we recorded.
This both supports and undermines my prediction. I did predict the trends that the higher the concentration of the acid, the faster the gas was collected. I also predicted this for the same scientific reasons that I mention above the diagram. But in my prediction, I believed that the rate of reaction would be five times faster in 100% acid than in 20% acid, in fact it was more than that, but contrary to that on my graph the line of best fit misses the point I plotted for the rate of reaction at 100% acid, and it crosses instead at 1.5mils/sec which is five times as fast as the rate of reaction at 20% acid. I did account for the slowing down of reaction explained in the diagram above, but I did not realize how much it would account for.