Investigating the reaction between Marble Chips and Hydrochloric Acid.
Investigating the Reaction between Marble Chips and Hydrochloric Acid
Background Information
The reaction rate tells us how fast or slow a chemical reaction is and there are four factors that can affect this greatly, they are:
Concentration: An increase in concentration means there are more particles. More particles means there will be more collisions. This should increase the reaction rate.
Surface Area: When one of the reactants is solid, the reaction can only take place at the surface of the solid. Breaking the solid into smaller pieces will increase the surface area exposed to the other reactant. This should increase the reaction rate.
Temperature: Since temperature is a measure of the motion of particles, increasing the temperature will cause the particles to move faster. When particles move faster, more collisions occur and the collisions are more violent. This should increase the reaction rate
Catalysts: Catalysts are substances that change the rate of a chemical reaction without being changed in the reaction. Catalysts are most often used to speed up a chemical reaction. They do so by changing the steps needed between reactants and the formation of the products. If the number of steps can be reduced, the reaction rate should increase. The Reaction Rate is often called the "Collision Theory", which describes the way temperature, concentration and surface area of the solid reactant affects the rate of reaction, by affecting collisions from particles.
Particles react when they collide with sufficient energy. At a higher temperature collisions are more frequent and they also have more energy, both because particles are moving faster. At a higher concentration collisions are again more frequent, as there are more reactant particles in the liquid. Increase surface are of the solid again increases the frequency of collision between reacting particles, as the liquid reactant has greater contact with the solid one. Adding a catalyst can also increase the rate of reaction, but there is not one used in this experiment.
Light intensity: Light intensity can have a very small affect on a reaction.
Aim
My aim is to investigate the affect on the volume of carbon dioxide gas produced inside a time limit if I vary the concentration (mol) of Hydrochloric Acid when it is reacted with Marble Chips. To make this a fair test I shall keep every variable the same except the one I am investigating (Concentration).
For this investigation I shall be investigating the reaction between calcium carbonate and hydrochloric acid. The products of the reaction between calcium carbonate and hydrochloric acid are calcium chloride and carbon dioxide. Below are word and symbol equations for the experiment:
Calcium Carbonate + Hydrochloric Acid Carbon Dioxide + Water + Calcium Chloride
CaCO3 + 2HCl CaCl2 + H2O + CO2
Prediction
I predict that as the concentration of the hydrochloric acid decreases, so does the value recorded of the volume of carbon dioxide gas collected, at each time station (the time stations are at 30 second intervals at: 0 seconds, 30 seconds, 60 seconds, 120 seconds and 150 seconds).
I predict that in the later stages of the timed reaction, the rate will slow down. I was able to make these predictions due to my background knowledge on how the variable of concentration of an acid affects the rate of a reaction (the more concentrated the acid is, the quicker the reaction).
Apparatus
For the experiment, I shall need:
* A Stopwatch
* A Gas Syringe
* Hydrochloric Acid
* Marble Chips (with diameters of between 2mm and 4mm)
* A Spatula
* A Delivery Tube
* A ...
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I predict that in the later stages of the timed reaction, the rate will slow down. I was able to make these predictions due to my background knowledge on how the variable of concentration of an acid affects the rate of a reaction (the more concentrated the acid is, the quicker the reaction).
Apparatus
For the experiment, I shall need:
* A Stopwatch
* A Gas Syringe
* Hydrochloric Acid
* Marble Chips (with diameters of between 2mm and 4mm)
* A Spatula
* A Delivery Tube
* A Conical Flask
* A Measuring Cylinder
* 2 Beakers
* Rubber Tubing
* Water
* A Boss Clamp
* A Stand
* Plastic Tube Connectors
* A Weighing Boat
* A Teat Pipette
* A Top Pan Balance
Safety
In order to ensure a safe experiment, I shall take the following precautions:
* I shall wear safety goggles and a lab coat, as even though the acid is not extremely corrosive, it is still concentrated enough to provoke injuries.
* As there is water involved in the experiment (for diluting the hydrochloric acid, I have to be extremely careful not to spill it as accidents (leading to injuries could be induced).
* I will not run in the laboratory, as I could have an accident, injuring myself and/or others.
* In the unlikely event of an accident occurring, I shall evacuate others and myself from the direct surrounding areas and notify the lab supervisor immediately.
Method
I chose to use a gas syringe instead of the method of water displacement, as in my opinion it presented more accurate values of the volume of gas that had been collected. I believed this as I tried both methods in a preliminary experiment that I carried out. I chose to use distilled water, as tap water may have contained traces of calcium carbonate, or other substances which may have influenced the reaction.
After setting up the apparatus as shown in the diagram, I weighed out 1.0 gram of Marble Chips (using the weighing boat and the top pan balance), and measured out 40ml of a specific concentration of hydrochloric acid (using the measuring cylinder and water to dilute the acid if it needed to be less concentrated than 2molar), using the table below to give reference as to how to dilute the acid:
Concentration of Acid
Volume of acid to take
Volume of water to add
Total volume
(mol/dm3)
(ml)
(ml)
(ml)
2
50
0
50
.8
45
5
50
.6
40
0
50
.4
35
5
50
.2
30
20
50
25
25
50
0.8
20
30
50
0.6
5
35
50
0.5
2.5
37.5
50
I then put the acid and the chips in the conical flask, secured the bung in it, and started the stopwatch.
Every 30 seconds till 150 seconds, I recorded the value of the volume of carbon dioxide gas that had been collected in the gas cylinder. I repeated this experiment in exact detail, three times for each of the five concentrations that I used. The only variable that was changed during the whole experiment was the concentration of the acid, so this meant that in every run-through of the experiment I was using exactly 1.0 gram of Calcium Carbonate chips.
When I had finished the experiment, I recorded the data I had collected, plotted it into a table of results, and using the table of results, plotted 5 graphs. Each graph shows the average results obtained for each different value of the concentration (molar) of the hydrochloric acid (2,1.8,1.6,1.4,1.2). Each graph uses the label "Volume of Carbon Dioxide gas collected (Millilitres)", on the x-axis, and the label "Time passed in reaction (Seconds)", on the y-axis.
Results
Below is a table which displays the results I obtained from the experiment.
Amount of Carbon Dioxide gas already collected (ml) at these set periods of time (seconds) in the reaction
Acid Concentration (Molar)
0
30
60
90
20
50
2
0
24
48
64
86
n/a
2
0
25
50
66
93
n/a
2
0
20
43
62
82
98
Average Results for 2 Molar Acid
0
23
47
92
87
n/a
.8
0
23
42
61
81
97
.8
0
21
39
59
78
93
.8
0
22
39
60
81
95
Average Results for 1.8 Molar Acid
0
22
40
60
80
95
.6
0
5
30
47
60
80
.6
0
8
40
55
70
90
.6
0
8
33
48
75
91
Average Results for 1.6 Molar Acid
0
7
34.3
50
68.3
87
.4
0
1
9
33
41
57
.4
0
5
32
40
57
72
.4
0
7
34
45
56
73
Average Results for 1.4 Molar Acid
0
4.3
28.3
39.3
51.3
67.3
.2
0
0
8
28
39
50
.2
0
1
9
31
39
51
.2
0
3
23
31
42
52
Average Results for 1.2 Molar Acid
0
1.3
20
30
40
51
Analysis
From looking at each graph and comparing the straight line that my results produce, with the line of best fit that I have included, it is obvious to the human eye that my results are not completely true to my prediction. On each graph there is one or more plots that are not on the line of best fit (albeit only very marginally in all cases). The shape of each graph is nearly a perfect straight line, however the fact that they are not perfectly straight tells us that the method I used was not totally accurate.
In the case of every graph I have produced, the pattern my results show is that the more concentrated the acid, the higher the volume of gas recorded at each time-station. For example, below are the average volumes recorded at the second time station (30 seconds into the duration of the reaction), for each different concentration. They are displayed below in ascending concentration.
My results agree very closely with my prediction that "...as the concentration of the hydrochloric acid decreases, so does the value recorded of the volume of carbon dioxide gas collected, at each time station..." There is not a single result that disagrees with this prediction. The fact that each graph has produced straight lines that are almost exactly the same as its line of best fit, adds reliability to this prediction. The increase in the line of each graph does seem to be proportional, as the gradient of the line seems to increase by roughly the same amount between each recorded mark.
The reaction rate did not seem to show any signs of slowing down in the latter stages of the timed reaction, which was an opposite event to that I had predicted. This was almost certainly due to the fact that the experiment was not timed for long enough.
One/some of the factors that can speed up a reaction that I referred to in my "Background Information" section may be to blame for any inaccurate results. It cannot be a catalyst that is responsible, because as mentioned previously, a catalyst was not used in the experiment. Concentration was the only variable that I was concentrating on, thus it cannot possibly be this factor.
The temperature of the acid/room may have affected the reaction, but the differences in temperatures would have been so small that they would not have been significant enough to induce anomalous results. The surface area of the marble chips however were very varied (diameters of between 2mm and 4mm), therefore meaning that the variable of surface area was also controlling the results that I obtained from the experiment in addition to that of concentration. However I knew the precise concentration of the acid that I was using for every step of the investigation, but only had a limited idea of the surface areas that the chips possessed.
Conclusion
In my conclusion to this investigation, I have ruled that the experiment that I carried out was not scientific enough. Instead of only one variable (concentration) being used as I had planned, two (concentration and surface area) were used and I didn't realise this at the time. Even though the differences of the second variable (surface area) were small, these differences will still have had an affect on the experiment. Therefore my results are not accurate enough for a direct conclusion to be made.
Evaluation
My plan worked extremely well. The results that the investigation provided me with give me reason to believe that my prediction that "...as the concentration of the hydrochloric acid decreases, so does the value recorded of the volume of carbon dioxide gas collected, at each time station...", is reliable. My prediction that "... in the later stages of the timed reaction, the rate will slow down.", was not supported in any way by the results that I recorded. I still however support that this prediction was correct and the reason I have, and strongly stand by for its not working, is that the reactions were not timed for long enough, as there were still large amounts of marble chip reacting with the hydrochloric acid meaning there was still a long time before one of the reactants would be completely diminished.
As you can interpret by studying the data that the experiment provided me with, there are few results that didn't appear on their graph's line of best fit. This tells us that the method I used was not totally accurate. All my graphs appear to show fairly accurate results, as each graph's plots appear to produce a near perfect straight line. However, the results cannot be very accurate, as they do not create perfectly straight lines.
There is a realistic possibility that the gas syringe may have encountered friction while collecting gas. This would have affected the results obtained, as the syringe would not have allowed any more gas to enter until the pressure of the trapped gas built up high enough to overcome the resistance (the friction in the gas cylinder). In order to improve this experiment I would have to use a gas syringe that encountered no friction when in operation.
It was obviously impossible for me to start the stopwatch at the exact time that the reaction started, for each individual experiment (due to my limited selection of apparatus). This meant that the stopwatch was started a small period of time after a reaction started, thus meaning there would already be gas in the syringe when the timing started, making my results inaccurate. However, if this was the only error inducing factor in the experiment I would more than likely be unable to unearth it, because as the error would be repeated for every individual experiment, it would not show make much difference to the trend line as it would be averaged out. I could have improved this performance factor by obtaining another person to start the stopwatch for me me, thus reducing the extremity of the problem.
Also, when I dropped the marble chips into the conical flask (which started the reaction with the hydrochloric acid), I then had to secure the bung back in the head of the flask. This means that small amounts of gas will have escaped from the flask instead of making its way to the gas syringe. I could have improved this performance factor by obtaining another person to do this for me, thus reducing the amount of gas lost.
There is a chance that when recording values of the volume of gas obtained, I may have misread the value that the syringe showed, therefore recording inaccurate results. There is also a possibility that when I reset the syringe for another experiment, that I didn't set the value indicating the volume of gas contained exactly to "0". This would also have provided me with inaccurate results.
The gas syringe measures the volume of the gas it contains, every cm3, meaning that for some recording I found myself having to make split-second choices, estimating which marked value the gas volume was closer to. This will probably have created inaccurate results.
The top pan balance gives its readings to 0.01g. This means that there was no way of telling that the marble chips being weighed had a total weight of exactly 1.0g. This would also have therefore have induced inaccurate results being recorded. In order to improve this experiment I would have to use a top pan balance that gave more precise readings.
I think that my results are accurate enough to be used as a rough guideline for future investigations, to let the scientists know whether they are recording extreme anomalous results, but this is about all they are good for. They are definitely not accurate enough for a direct conclusion to be drawn from them, as I have outlined so many aspects of my method that may have induced inaccurate results.
Because the surface areas of the marble chips were varied (with diameters of between 2 and 4 mm), the experiment was subsequently not scientific enough. In order to improve this experiment I would have to use marble chips with less differences in their surface areas, e.g. diameters of between 2 and 2.5mm. I could also have improved the experiment by narrowing the range of the independent variable (concentration).
Centre Number - 25176 08/05/2007 Candidate No. 9014
Centre Name - Uppingham School 1 Candidate Name Callum Bush