Investigate how concentration of hydrochloric acid (HCL) affects its reaction with calcium carbonate (CaCO3).
Chemistry Coursework - Rate of Reaction Investigation
Planning
Aim
Background Information
Collision Theory
For particles to react, two things must happen:
) The particles must collide with each other.
2) The particles must collide with enough energy. This initial energy is known as activation energy, and it's needed to break the initial bonds
If the collision has enough energy the reaction will take place and by products will be formed.
If the collision does not have enough energy no reaction will take place, instead the particles will just bounce away from each other.
The rate of reaction depends on how many successful collisions there are in a given amount of time.
Factors that affect the rate of reaction:
There are four factors that can affect the rate of reaction:
) Temperature
If you increase the temperature, the rate of reaction will increase. This is because at low temperatures the particles don't have as much energy, but when they are heated they take in energy which makes them move faster and collide more often. This means the collisions also have more energy, which makes more of the collisions successful. This is why as you increase the temperature the rate of reaction increases.
2) Concentration
The rate of reaction increases with concentration because when the acid is more concentrated, there are more acid particles in a given volume. This means there is a better chance of a successful collision occurring.
In dilute acid, like the one shown below, there are not so many acid particles. This means there is not as much of a chance of an acid particle hitting a limestone atom.
In more concentrated acids, like the one shown below, there are more acid particles. There is now more of a chance of a successful collision occurring.
The reaction of limestone with hydrochloric acid shows that with time the reaction slows down. This is because at the start of the reaction there are plenty of limestone atoms and acid particles. But as the time goes by these particles get used up during successful collisions. After more time there are less limestone atoms, and the acid is less concentrated. As a result of this, the reaction slows down. This is shown in the diagram below:
3) Surface Area
The rate of reaction increases as the surface area of the reactant increases. This is because when the surface area is small, the acid particles can only collide with the outside of it to get to the middle. However, if the reactant was powdered or in smaller
lumps the atoms are more exposed; this allows the acid a larger surface to collide with. This is shown in the diagram below:
4) Catalyst/Inhibitors
Catalysts and inhibitors can also affect the rate of reaction. Catalysts do not take part in the reaction, do not get 'used up' and can be used again. A positive catalyst speeds up a chemical reaction by encouraging bond breaking. Because the activation energy is lowered, the particles need less energy to react and the reaction rate increases. Inhibitors act in the opposite ways by increasing the amount of activation energy needed; this increases the rate of reaction.
Acid Rain
Acid rain is more acidic than normal rain and forms through a complex process of chemical reactions involving air pollution. The two most important pollutants that contribute to the formation of acid rain are oxides of nitrogen and sulphur dioxide, which react with moisture in the atmosphere to form nitric and sulphuric acid. The sulphur and nitrogen compounds that contribute to acid rain mainly come from manmade sources, such as industries and utilities. Emissions also come from automobiles and other forms of transportation and industrial processes, such as smelting.
Acid rain can harm forests and crops, damage bodies of water, and contribute to the damage of statues and buildings. Researchers are considering the possible effects of acid rain on human heath. These acidic pollutants can be deposited through rain, snow, fog, dew, or sleet. Large quantities can also be deposited in a dry form through dust.
Pollutants that contribute to acid rain may be carried hundreds of miles before being deposited on the earth. Because of this, it is sometimes difficult to determine the specific sources of these acid rain pollutants.
Hypothesis
I believe that as the concentration of hydrochloric acid (HCL) increases, the rate of reaction with calcium carbonate (CaCO3) will increase.
Prediction
In my hypothesis I stated that predict that as the concentration of hydrochloric acid (HCL) increases, the rate of reaction with calcium carbonate (CaCO3) would increase.
I believe this because at a higher concentration there will be more hydrochloric acid molecules in a given volume. This would mean that there would be I higher chance of the
Calcium carbonate molecules colliding with the hydrochloric acid and reacting. According to the theory, increasing the concentration would increase the rate of concentration.
However, during my background information research I found out an important factor. The reaction of calcium carbonate with hydrochloric acid shows that with time the reaction will slow down. This is because at the start of the reaction there are plenty of magnesium atoms and acid particles. But as the time goes by these particles get used up during successful collisions. After more time there are less marble atoms, and the acid is less concentrated. As a result of this, the reaction slows down.
I have come to this conclusion because of the research I did on collision theory in my background information. Collision Theory states that to react, particles need to collide successfully. Also, the particles have to react with enough energy to break the initial bonds between the particles; this energy is known as activation energy. If there is not enough energy in the collision, the particles will bounce off each other and no reaction will take place. This is an unsuccessful collision.
The reaction will cause by products to be formed, the word equation for this reaction is:
Calcium Carbonate + Hydrochloric Acid Calcium Chloride + Water + Carbon dioxide
The balanced symbol equation for this reaction is:
CaCO3 + 2HCL CaCl2 + H2O +CO2
There is also another thing that I want to predict. I believe that if the concentration of acid is doubled, for example from 2M to 4M, the rate of reaction will double. I believe this because if the concentration doubles, I have found out that there will be twice as many acid molecules. This, should then double the chance of the calcium carbonate atoms and the hydrochloric acid molecules successfully colliding and reacting.
Apparatus
* Cone shaped conical flask
* Measuring cylinder
* Delivery tube
* Gas syringe
* Bung
* Stop clock
* Goggles
* Mat
* Balance
Chemicals Required
* Hydrochloric acid (1, 2, 3 and 4 molar)
* Calcium carbonate chips (small, medium and large)
Diagram
Safety
There are numerous precautions that I will take to make the experiment a safe one.
This experiment involves the handling of chemicals and glass, which are hazardous. Therefore, we need to be extremely careful when handling them.
Hydrochloric Acid
Nature of hazard - Higher molar acid may cause irritation to the skin. Blindness can actually occur if it comes into contact with your eyes. Lower molar acid may still harm the eyes or a cut if it drops on it.
Control measures - Wear eye protection for all but the most dilute solutions. Try to use the lowest concentration possible, using the smallest volume possible as well. Wear protective gloves if anything more than tiny amounts of concentrated acid are handled. Avoid breathing gas or fumes from the concentrated solutions e.g. by use of a fume cupboard. Do not hold acid bottles in the air when pouring, try to use a desk. Handle with extreme care and precaution.
Emergency Procedure - If acids is dropped on the skin, wask thoroughly and seek medical advice. If the acid is splashed into the eyes, wash thoroughly and seek medical advice. If the acid is spilt on a desk or the floor, wash up the acid thoroughly wearing gloves with a damp cloth. If the acid is accidentally consumed, drink plenty of water, and seek medical advice.
Calcium Carbonate
There is not really a danger with the calcium carbonate chips unless it is swallowed. If they are, seek medical advice straight away.
Glass Equipment
Nature ...
This is a preview of the whole essay
Emergency Procedure - If acids is dropped on the skin, wask thoroughly and seek medical advice. If the acid is splashed into the eyes, wash thoroughly and seek medical advice. If the acid is spilt on a desk or the floor, wash up the acid thoroughly wearing gloves with a damp cloth. If the acid is accidentally consumed, drink plenty of water, and seek medical advice.
Calcium Carbonate
There is not really a danger with the calcium carbonate chips unless it is swallowed. If they are, seek medical advice straight away.
Glass Equipment
Nature of hazard - If glass equipment is broken, the sharp glass can cause cuts to the skin. If the glass has been in contact with glass it can also contaminate blood.
Control measures - Handle with extreme care and precaution, keeping the glass equipment well away from bench edges. Dispose of broken glass using a brush and shovel.
Emergency Procedure - If you are cut, wash the injured area thoroughly with plenty of water, then seek medical advice.
I will keep the lab clear of bags, jackets, etc on the floor and avoid distracting students from their experiments. If I didn't take this precaution someone could be injured in a number of ways. E.g. slipping on a jacket left on the floor.
Preliminary Test
There are a number of things I need to find out before I write up my final method. I need to find out what volumes, times and measurements I will use in my real experiment. To find out the answers to these things I will conduct a preliminary test.
The experiment will be to set a fixed volume of gas that has to be produced, and take eight readings changing the molar of the hydrochloric acid, and the size and mass of calcium carbonate chips each time. These readings will be taken from the reaction between hydrochloric acid and calcium carbonate.
Mass of CaCO3 (g)
Size of Chip (L, M, S)
Volume of Acid (cm3)
Concentration (M)
Time to get to 100cm3 (seconds)
Comments
5
S
50
4
6.00
Way too fast, increase chip size
5
M
50
4
5.00
Still too fast, lower mass of chip, increase size of chip, lower molar
.4
L
50
2
380.00
Way too slow, lower size of chip
.4
M
50
2
60.00
Still slow, lower size of chip and molar
.4
S
50
80.00
Slow but fine (is the 1 molar reaction)
.4
S
50
2
81.00
Very good, just right
.4
S
50
3
57.00
Excellent, just right
.4
S
50
4
39.00
Fast but fantastic (is the 4 molar reaction)
In the test I will set the volume of hydrochloric acid used at 50cm3. The volume of gas that has to be reached will be 100cm3. By changing the measurements I will see whether the experiment is better than the last. I will keep changing the measurements until I get a good set of results. This set of results should allow me to take at least six measurements when the reaction is at its fastest, and shouldn't be too long when it is at its slowest (no more than 280 seconds.) Also, the volume of acid amount and CaCO3 chips should be economical. Once I find a good set of results, I will test these measurements at 1, 2, 3 and 4 molar. This will allow me to tell how long the real experiment will take at each of the respective molars. If the times are right for me, I will use these measurements in my real experiment. The results I got are shown below:
My Adaptation of the preliminary test
I conducted eight different experiments in my preliminary test.
My first set of measurements gave a time that was way too fast at 6 seconds. I would not be able to take measurements in my real experiment if I chose these measurements, because it is too fast. To slow the experiment down I increased the chip size to medium. The second experiment was still too fast at 15 seconds. I would still not be able to take measurements in my real experiment if I chose these measurements, because it is still too fast. I decided to lower the mass of the chips to 1.4g, increase the size of the chip to large and lower the molar to 2. This would help to increase the time.
The third experiment was way too slow at 380 seconds. To help lower the time, I decided to lower the size of the chip to medium.
The fourth experiment was still a little slow at 160 seconds. To try and lower the time I lowered the chip size to small and lowered the molar to 1.
The fifth experiment was slow at 180 seconds, but this was fine as this was the molar 1 reaction. It was bound to be slow. I decided to use these measurements, but I waned to see how the time was at the other molars. I increased the molar to 2 to see how this was.
The sixth experiment at 81 seconds was just right for a molar 2 reaction. I increased the molar to 3 to see how this was.
The seventh experiment at 57 seconds was brilliant for a molar 3 reaction. I increased the molar to 4 to see the fastest time the reaction would have.
The eighth experiment at 39 seconds was fantastic for a molar 4 reaction. It was bound to be quick. It is good because it is still not too quick.
I decided that these were the right measurements, because the slowest reaction (1 molar) was not too slow, and the fastest reaction (4 molar) was not too fast.
The measurements I will therefore use for my main method will be:
Mass of CaCO3 (g)
.4
Size of Chip (L, M, S)
S
Volume of Acid (cm3)
50
These measurements look very good. Using a mass of 1.4g for the chips will be economical. The volume of acid at 50cm3 also seems reasonably economical. It is also safer to use a lower volume of acid, which is another good point about the volume of acid I have chosen.
My main method for my real experiment is shown on the next page:
Main Method
Now I will show how I plan to get my results, I will show my method in a step-by-step way:
. Take the cone shaped conical flask.
2. Measure 50cm3 of 1 molar hydrochloric acid in a measuring cylinder. Keep the cylinder on the table and bend your knees to keep an eye on the volume of acid.
3. Weigh 1.4g of small calcium carbonate chips.
4. Connect the delivery tube up to the gas syringe.
5. Connect the other end of the delivery tube up to the conical flask.
6. Pour the 50cm3 of 1 molar hydrochloric acid into the conical flask.
7. Add the 1.4g of small calcium carbonate chips to the conical flask with hydrochloric acid in it.
8. Put on the bung and start the stop clock immediately.
9. Every 10 seconds measure the volume of hydrogen gas given off, by reading the 0-100 side on the gas syringe.
0. When the barrel on the gas syringe has stopped moving the experiment has ended.
1. Record results in a suitable table.
2. Clean equipment and dry.
3. Repeat the experiment using 1 molar hydrochloric acid at least 1 more time (2 more if you have the time), in order to gain and average of results, so results will be accurate.
4. Clean equipment and dry.
5. Repeat the experiment using 2, 3 and 4 molar hydrochloric acid using the above method.
Fair testing/variables?
There is one variable in my experiment, this is concentration. I will be varying the concentration because I will be using 1 molar acid, 2 molar acid, 3 molar acid and 4 molar acid.
There are various things that I will have to do to ensure that I get fair, accurate and reliable results. These are:
* I will try to keep the surface area of the calcium carbonate chips the same. If they were not the same, I would get inaccurate and unreliable results. This is because the surface area of the calcium carbonate chips affects the rate of reaction with the hydrochloric acid. If we increase the surface area, the rate of reaction with the hydrochloric acid will increase. This is because when the surface area is larger, more particles are exposed for the acid to collide with. However, if the surface area is small, the acid has to first react with the exposed reactant, then work its way in to the middle. This slows down the rate of reaction. I will use only one size of calcium carbonate chip (small). Obviously, not every calcium carbonate chip will be the same size, but they will be roughly the same size.
* For the experiment to be a fair one, I also need to keep the temperature of each experiment the same. The temperature, if different all the time, will create inaccurate and unreliable results. Increasing the temperature will affect the reaction in two ways:
. The particles are moving faster, so we get more collisions in a period of time.
2. The particles have more energy, so we get more successful collisions.
To try to avoid having different temperatures for each experiment I will not warm up any of the reactants. I will carry out the experiments at room temperature; this will hopefully stop some of the errors that could occur if I did the experiments at different temperatures.
We only want to find out the effect of concentration on the rate of reaction in this experiment; therefore, we do not want to create another variable by having different temperatures.
* Another factor that I will have to keep the same to have a fair test is the mass of the calcium carbonate chips. The larger the mass of the calcium carbonate chips, the faster the rate of reaction with the hydrochloric acid will be. This is because the acid will have more chips to react with, increasing the number of collisions. This, in turn increase the possible amount of Carbon dioxide there is to be produced. So this does not happen, before each experiment I will accurately measure the mass of the calcium carbonate chips I use on an electronic balance.
* I will also keep the volume of the acid the same. This can affect the number of hydrogen ions the calcium carbonate can react with. Although the amount of hydrogen ions present in any given volume will not increase, there will be more of it and therefore this will increase the rate of reaction. So this does not happen, I will accurately measure the amount of acid I want using a measuring cylinder. The volume will be kept constant.
* Catalysts and inhibitors can also affect the rate of reaction. Catalysts do not take part in the reaction, and do not get 'used up' and can be used again. A positive catalyst speeds up a chemical reaction by encouraging bond breaking. Because the activation energy is lowered, the particles need less energy to react and the reaction rate increases. Inhibitors act in the opposite ways by increasing the amount of activation energy needed; this increases the rate of reaction. So that my experiment is as accurate as possible I will not add any catalysts or inhibitors to my experiment. This will hopefully ensure that my experiment is not affected by catalysts or inhibitors.
Results
Below are the four results tables in which the data has been arranged into:
Concentration - 1 molar
Volume of Carbon Dioxide Gas Produced (cm3)
Time (seconds)
st Run
2nd Run
Average Of Both Runs
0
0
0
0
0
4
5
5
20
5
6
6
30
7
7
7
40
9
0
0
50
2
1
2
60
5
4
5
70
8
9
9
80
22
21
22
90
27
26
27
00
32
31
32
10
37
36
37
20
42
40
41
30
48
47
48
40
53
51
52
50
57
55
56
60
62
60
61
70
67
66
67
80
71
72
72
90
77
76
77
200
80
80
80
210
85
84
85
220
88
88
88
230
92
91
92
240
95
94
95
250
98
99
99
260
00+
00+
-
Concentration - 2 molar
Volume of Carbon Dioxide Gas Produced (cm3)
Time (seconds)
st Run
2nd Run
Average Of Both Runs
0
0
0
0
0
2
0
1
20
24
9
22
30
35
30
33
40
48
41
45
50
58
55
57
60
71
68
70
70
88
82
85
80
00+
93
-
90
00+
-
Concentration - 3 molar
Volume of Carbon Dioxide Gas Produced (cm3)
Time (seconds)
st Run
2nd Run
Average Of Both Runs
0
0
0
0
0
6
4
5
20
31
29
30
30
42
40
41
40
55
57
56
50
68
70
69
60
87
89
88
70
00+
00+
-
Concentration - 4 molar
Volume of Carbon Dioxide Gas Produced (cm3)
Time (seconds)
st Run
2nd Run
Average Of Both Runs
0
0
0
0
5
2
2
2
0
9
22
21
5
28
30
29
20
40
41
41
25
48
52
50
30
55
58
57
35
65
65
65
40
75
75
75
45
86
90
88
50
95
98
97
55
00+
00+
-
In order to be as accurate as possible I repeated each experiment two times. This allowed me to calculate an average which would lessen the possible errors or anomalies.
To work out the average for the volume of CO2 gas produced I:
. Add the values of the 1st and 2nd runs together
2. Divide this total by two.
3. Round up or down the number you get to the nearest whole number.
I did my averages to whole numbers because when I was doing the experiment I could only record the volume of CO2 gas to whole numbers. I could not take measurements of the CO2 gas to one decimal place, so I decided not to do that when I was doing my averages.
I did not take an average of all the runs. For example, I could not take an average of the two runs for 55 seconds on 4 molar hydrochloric acid because each showed that more than 100cm3 CO2 gas was produced. As each showed that more than 100cm3 CO2 gas was produced it was impossible for me to take an average because I did not know the two exact values. For example, one of the values could be 102 or 104 and the other could be 105 or 107. I only took an average of results that had a definite value.
Another thing I want to mention is that for molar 4 hydrochloric acid, I shortened the time interval for taking measurements of the gas to 5 seconds. This was because I wanted to get at least eight readings. If I used the time interval of 10 seconds as I did for all of the other experiments I would have had only seven readings. Having more readings made my experiment more accurate, which is why I wanted to have at least eight readings in the first place. I felt this was a suitable number of readings as it was not too many and not too few.
Analysis
If you turn to my next page you will see my graph.
The graph shown on the last page shows the volume of CO2 gas produced (cm3) against time (seconds). The time (seconds) is shown on the x-axis while the volume of CO2 produced (cm3) is shown on the y-axis.
The points on the graph were obtained by taking an average of the two runs I did for each molar. Once I had the average results, I simply plotted them on the graph. However, I did not take an average of all the runs. For example, I could not take an average of the two runs for 55 seconds on 4 molar hydrochloric acid because each showed that more than 100cm3 CO2 gas was produced. As each showed that more than 100cm3 CO2 gas was produced it was impossible for me to take an average because I did not know the two exact values. For example, one of the values could be 102 or 104 and the other could be 105 or 107. I only took an average of results that had a definite value. As a result of this, not all the lines on my graph go to 100cm3. The 1 molar line goes to 99cm3, the 2 molar line goes to 85cm3, the 3 molar line goes to 88cm3 and the 4 molar line goes to 97cm3.
From looking at the graph I can immediately tell that by increasing the concentration of the hydrochloric acid, the rate of reaction increases. I can also tell which concentration is fastest by looking at my graph. I can tell this because the fastest concentration (4 molar) is the steepest line. When the line is steeper it means that it takes less time for that molar to produce 100cm3 of CO2 gas.
I can back this up by comparing how long the 1 molar and 4 molar hydrochloric acids took to produce at least 100cm3 of CO2 gas. The 1 molar acid took 260 seconds while the 4 molar acid took 55 seconds. This proves that by increasing the concentration of the hydrochloric acid, the rate of reaction increases.
Now I will calculate the gradient for each line. This is calculated by the 'change in y divided by the change in x' I have decided to take the gradient from the first 20 seconds of the experiment, because this is where the reaction should be at its fastest.
The gradient above shows the number of cm3 of carbon dioxide produced in a second (cm3/s).
From the gradients I can again see that as the concentration of the hydrochloric acid is increased so is the rate of reaction. This is because the gradient of the line increases when the concentration is higher. When the gradient of the line is high, it means the rate of reaction is high. Also if the line is steeper it means the gradient will be higher.
In my prediction I stated that predict that as the concentration of hydrochloric acid (HCL) increases, the rate of reaction with calcium carbonate (CaCO3) would increase. Now I will use my scientific knowledge to prove why the rate of reaction increases as the concentration of the hydrochloric acid increases.
The rate of reaction increases with concentration because when the hydrochloric acid is more concentrated, there are more hydrogen particles in a given volume. As there are more hydrogen particles there is more of a chance that the calcium in the calcium carbonate will collide with the hydrogen particles. When there are more collisions there will be more successful collisions, this will increase the rate of reaction. However, with time the reaction will slow down. This is because at the start of the reaction there are plenty of calcium atoms and hydrochloric acid particles. But as the time goes by these particles get used up during successful collisions. After more time there are less calcium atoms, and the hydrochloric acid is less concentrated. As a result of this, the reaction slows down. This is not shown clearly on the graph because I could only measure the gas to 100cm3, I could not see the ending of the reaction when it would slow down.
In my prediction, I also stated that if the concentration of acid is doubled the rate of reaction would double. I believed this because if the concentration doubles, I found out that there would be twice as many acid molecules. This should have then doubled the chance of the calcium carbonate atoms and the hydrochloric acid molecules successfully colliding and reacting.
However, by taking readings off the graph I can see that this is not the case. At 40 seconds on the 1 molar line 8.5cm3 gas has been produced. At 40 seconds on the 2 molar line 43cm3 gas has been produced. I can see that the effect of doubling the concentration more than doubles the rate of reaction.
I can also prove this point by looking at the gradients. At 1 molar the gradient was 0.18cm3/s, at 2 molar the gradient was 1. From this I can again see that the effect of doubling the concentration more than doubles the rate of reaction.
The results did not fully support my prediction, reasons for this could have been:
* The gas syringe was sometimes jerky.
* The surface area of the calcium carbonate chips varied.
* The room temperature could have varied.
* The temperature of the conical flask could have changed.
* The temperature of the calcium carbonate chips could have changed.
* The amount of light given to each experiment might have been different, for example, because of an open window letting light in.
* Human error in the measurement of things in the experiment.
* Water in the conical flask.
* The pureness of the calcium carbonate chips.
* Layers of coating on the calcium carbonate chips.
* The bung could have been placed on the conical flask at different times.
These factors would have affected my set of results; therefore the gradients I got would have been affected. They could be the reason why the gradients I got did not fully support the prediction I made.
I have explained each factor listed in detail in my Evaluation.
Evaluation
After doing my experiment I can say that it went reasonably well. This is because the results I got from the experiment were good enough to support my hypothesis that I made at the start which was:
"I believe that as the concentration of hydrochloric acid (HCL) increases, the rate of reaction with calcium carbonate (CaCO3) will increase."
There were a few things during the experiments that I found difficult, they are as follows:
* It was hard to put the bung on the conical flask as soon as the calcium carbonate chips had been put in. This would have let a little bit of gas out at the start of every experiment.
* It proved difficult to fully dry the conical flask and measuring cylinder after they had been washed with water. This was because it was hard to get the paper towel to the bottom of the conical flask, and especially the measuring cylinder. I just had to try my best. It could have resulted in some contamination of the acid.
On my graph I can see three anomalous points. They are as follows:
Concentration of acid - 1 molar
0 seconds - 5cm3 CO2 gas produced
20 seconds - 6cm3 CO2 gas produced
30 seconds - 7cm3 CO2 gas produced
40 seconds - 10cm CO2 gas produced
Concentration of acid - 2 molar
70 seconds - 85cm3 CO2 gas produced
I recognised all of the anomalies for the 1 molar set of results by looking at my graph. I looked at the molar 1 line of best fit and I could see that the points of the four anomalous results were not stuck closely to the line. All of the points of the anomalous results were above the line of best fit. From this I can tell that too much gas was being produced. There are not too many anomalies for the 1 molar acid set of results, so I can say that the results are pretty reliable. They do not affect my conclusion to the point where I doubt my prediction, because the set of results are still pretty reliable.
I recognised the anomaly for the 2 molar set of results by looking at my graph. I looked at the molar 2 line of best fit and I could see that the point of the anomalous results was not stuck closely to the line. The point of the anomalous result was above the line of best fit. From this I can tell that too much gas was being produced. There is only one many anomalies for the 2 molar acid set of results, so I can again say that the results are pretty reliable. It does not affect my conclusion to the point where I doubt my prediction, because the set of results are still pretty reliable.
There can a number of reasons why these anomalous results occurred. These reasons might have been:
* The gas syringe was jerky at times during the experiment. This was probably due to dirt or moisture being in the tube. It could have also just been a bad gas syringe. When the gas syringe jerked it affected the reliability of the results because it made it hard to read how much gas was being produced. It could have caused the anomalous results.
* The surface area of the calcium carbonate chips varied from piece to piece. In some cases the chips were found to be very small and in others they could be a lot larger. This would have affected the reliability of the results. Smaller chips have a larger surface area, which would lead to an increase of reactant particles being exposed. As more of the reactant would be exposed the rate of reaction would be generally faster. Larger chips have a smaller surface area, which would lead to a decrease of reactant particles being exposed. As less of the reactant would be exposed the rate of reaction would be generally slower. This could have caused the anomalous results.
* The room temperature could have varied. This could be due to someone opening a window, making the room colder. If the room was warmer it could lead to an increase in the rate of reaction. This is because the particles would have more kinetic energy, therefore they would move around more quickly. This would increase the chances of a successful collision, causing the rate of reaction to increase. If the room was colder it could lead to a decrease in the rate of reaction. This is because the particles would have less kinetic energy, therefore they would move around more slowly. This would decrease the chances of a successful collision, causing the rate of reaction to decrease. This could have caused the anomalous results.
* The temperature of the conical flask could have changed. This is because if I handled the conical flask for a long period of time, some heat energy from my hand would transfer to the conical flask. This would increase the rate of reaction because the conical flask would be warmer. Another reason why the temperature of the conical flask might have changed is if it were washed after each experiment in hot or cold water. This would have made the conical flask warmer or colder, increasing or decreasing the rate of reaction. This could have caused the anomalous results.
* The temperature of the calcium carbonate chips could have changed. This is because if I handled the calcium carbonate chips for a long period of time, some heat energy from my hand would transfer to the calcium carbonate chips. This would increase the rate of reaction because the calcium carbonate chips would be warmer. This could have caused the anomalous results.
* The amount of light given to each experiment might have been different. This could have been due to doing the experiment near to an open window. This would allow UV rays from the sun the reach the experiment, warming up the conical flask and its contents. This would increase the rate of reaction. This could have caused the anomalous results.
* Human error in the measurement of things in the experiment. Errors would have occurred when measuring how much gas was being produced, how much acid was put in the conical flask and the mass of the calcium carbonate. However, this is not very likely because I put in a lot of effort to measure things properly and accurately. This could have caused the anomalous results.
* Water in the conical flask. This is because when I washed the conical flask after every experiment it was very hard to completely dry it with the paper towels. This would have made the acid less concentrated meaning a slower reaction would take place. This could have caused the anomalous results.
* The pureness of the carbonate chips was unclear. One bottle of the chips had a powdery substance around it, whereas the other bottles of chips looked like marble. This could have increased or decreased the rate of reaction. However, we spotted this before the experiment and tried not to use the powdery chips. The powdery chips could still have been mixed with some of the marble looking chips, so it could have caused the anomalous results.
* The bung could have been placed on the conical flask at different times. Gas could escape before the bung was put on the conical flask, causing the gas given off to be lower then it should have been. The longer delay there was to put the bung on, the more gas could escape. This could have caused the anomalous results.
Despite these errors that might have taken place, I felt that my experiment was still reliable enough to come to a conclusion.
It wasn't that difficult to read the scale on the gas syringe or the measuring cylinder. The scale on both pieces of equipment was quite big, so it wasn't hard to measure the volume of acid and the gas produced accurately.
My mass measurements of the calcium carbonate chips were very accurate. This is because we used a good quality electronic balance provided by the school. It was very accurate, and it was easy to get all the mass measurements for the experiments the same. I decided to use a mass of 1.4g for my calcium carbonate chips.
My measurement of the acid in the measuring cylinder was quite accurate on the whole. I measured 50cm3 hydrochloric acid for our experiments. As I said in my method I kept the cylinder on the table at all times of pouring, and I bent my knees so my eye level was at the 50cm3 mark on the cylinder. I got the volume of acid on the line of 50cm3 at most times. However, there were times when the line was just over or under the 50cm3 mark. This was the case even when I had done all of the things to try and get 50cm3 of acid.
There are a few things that can be done to improve the reliability of my results, they are as follows:
* The experiment should be carried out on one day, although my group did this I heard other groups didn't. Some groups did the experiments over two days. That is why I'm making this point. Also no windows should be opened during the experiments so that the room would stay at a fairly constant temperature. Therefore the results would be more reliable as the temperature of the room would be more or less the same throughout.
* The surface area of the calcium carbonate chips can be kept constant by cutting equal cubes from a big block of calcium carbonate. Therefore if the chips used in each experiment had the same surface area, then this would also mean a fair test leading to more reliable results.
* All of the equipment should be checked before the experiment for faults. This includes the gas syringes. The gas syringes should be cleaned after every experiment, so that they don't jerk. However, this would be very time consuming and considering the time we had to do the experiment, it wouldn't always be possible.
* A new conical flask and measuring cylinder should be used after each experiment. This would solve the problem of having water in both pieces of the equipment after washing the equipment. However, this would obviously cost to much so wouldn't probably be able to be done.
* I could to more repeats of each experiment at each molar. This would improve the reliability of each set of results, as the average would be more accurate.
There are a number of ways in which you can extend the experiment, they are as follows:
* You could use a bigger range of concentrations of acid.
* You could use different reactants with hydrochloric acid, and compare how they react. For example, you could use magnesium.
* You could use different types of acids, for example, you can use nitric acid or sulphuric acid. Then you could compare how the reactant reacted with each acid, and see whether the same conclusions applied.
* You could use different variables, like temperature, and see whether the same conclusions applied.
Nabeel Tariq 10Z1
Dr. Clayson
