Investigation into the factors that effect the rate of reaction between calcium carbonate and hydrochloric acid
Investigation into the factors that effect the rate of reaction between calcium carbonate and hydrochloric acid
Planning
Background research
In order to design my experiment more accurately, I did some research to help me understand a bit more about reactions and how they occur:
A reaction is when two particles (reactants) join to for a new product(s).
Rate is a measure of how fast or slow something is.
The rate of a chemical reaction is how fast the reactants react together.
To measure the rate of a reaction, you should measure either the amount of reactant used up per unit of time, or the amount of product produced per unit of time.
Activation energy is the amount of energy required for the reactants to react successfully react. The reactants need a certain amount of energy. Any excess energy increases their chances of a successful collision.
The rate during a reaction doesn't remain constant. A reaction is more vigorous at first but slows down as the reaction goes on. This is because the longer the reaction takes place, the more of the reactants react, leaving fewer reactants with less chance of reacting.
For the reactants to be able to react, they have to successfully collide with each other. The chance of a successful collision can be increased or decreased by using many different factors:
Temperature: temperature alters the rate of a reaction by supplying the reactant particles with more energy. The more energy the reactants have, the faster they move around, therefore increasing the chance of colliding into one another and having a successful collision. Also, the more energy they get from the heat, the more particles have enough energy to react. This is called activation energy.
Generally, the greater the temperature, the faster the rate of a reaction. The rate doubles every 10°C.
Surface area: the greater the surface area of the reactants, the more particles are available, therefore the greater the likelihood of a successful collision occurring.
Concentration: concentration effects the rate of a reaction because the higher the concentration, the higher the concentration of particles, and therefore the greater the chance of a successful collision. As the rate doubles, the concentration doubles because they are directly proportional.
Catalyst: a catalyst is a substance that changes the rate of chemical reaction but remains chemically unchanged itself at the end of a reaction.
The Collision Theory ( the reaction rate): The collision theory is the most common one used to explain the facts about rates. The two main statements of this theory are:
Particles must collide beofre they can react.
The colliding particles between them must contain enough energy to cause bonds to break.
If a collision doesn't have enough energy, the molecules bounce apart and the collision has not been successful, however, in a collsion with enough energy, bonds are broken, new bonds are formed and the collision has been successful.
The collision theory affects all the variables I mentioned above:
Temperature: an increase in temperature leads to an increase in reaction rate. This is because the temperature of a system is a measure of the average kinetic energy of the particles in it. If the average kinetic energy of the particles increases, then more pairs of particles will have enough energy between them to collide successfully.
Surface area: an increase in surface area leads to an increase in reaction rate. This is because a greater surface area means a larger number of particles are exposed. Therefore, ...
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The collision theory affects all the variables I mentioned above:
Temperature: an increase in temperature leads to an increase in reaction rate. This is because the temperature of a system is a measure of the average kinetic energy of the particles in it. If the average kinetic energy of the particles increases, then more pairs of particles will have enough energy between them to collide successfully.
Surface area: an increase in surface area leads to an increase in reaction rate. This is because a greater surface area means a larger number of particles are exposed. Therefore, there will be a larger number of collision between particles.
Concentration: an increase in reactant concentration leads to an increase in reaction rate. This is because a higher concentration means a larger number of particles in a given volume. If there are more particles, there will be more collisions. More collisions means a larger number of successful collisions. Therefore the reaction rate will increase.
Catalyst: a catalyst can speed up the rate of a reaction. This is because the catalyst lowers the amount of energy needed for a successful collision. Therefore more collisions will be successful.
Hypothesis:
From this information, my main hypothesis would be 'How does changing the concentration of acid effect the rate of reaction between hydrochloric acid and calcium carbonate?'
My hypothesis therefore would be that as the concentration of the acid increases the rate of the reaction would increase.
Method
I have decided to investigate the effect of different concentrations of hydrochloric acid on marble chips (calcium carbonate). I want to see how much carbon dioxide will be produced in 1 minute, once the acid and the chips start reacting.
I carried out preliminary experiments to see what sort of ranges I was going to expect because I wanted to use the optimum concentration levels of hydrochloric acid and the optimum mass of calcium carbonate in order to make the experiment more effective and the results more accurate. I did this beforehand as I didn't have time to do this on the day of the actual experiment.
Apparatus:
* filter tubes to put the acid and marble in so that they could react
* bungs to seal the mouths of the filter tubes
* delivery tube to carry the gas from the filter tube to the syringe
* syringe to measure the amount of gas released in the experiment
* measuring cylinders to measure the amount of acid and water to be added to the marble
* clamp and stand to hold the syringe
* balance to measure the weight of the marble chips
* safety goggles because I am using acid
* boiling tube rack to hold the filter tubes
* marble chips, hydrochloric acid and water to react together
) Measure out 6 x 5g of calcium carbonate. Try and keep the size of the chips similar in order to reduce the amount of difference in surface area and therefore keeping the experiment as fair as possible.
2) Measure 10cm³ of hydrochloric acid into a measuring cylinder.
3) Place the marble in the filter tube. Pour the acid into the filter tube and as you do this start the time. Put a bung into the mouth of the filter tube to prevent any carbon dioxide form escaping.
4) Take readings off the syringe every 10s for 1 minute to see how much gas has been produced and record the results.
5) Repeat steps 1-4 using 8cm³ of hydrochloric acid and 2cm³ of water, 6cm³ of acid and 4cm³ of water, 4cm³ of acid and 6cm³ of water, 2cm³ of acid and 8cm³ of water, and finally, 10cm³ of water.
Before the apparatus was set up, the experiment had to be planned as fairly as possible. This involved making sure that I was changing only one variable, i.e. all the others remained constant. Firstly, the mass of the chips was kept constant at 5g throughout the experiment. From research and the preliminary experiments, I know that surface area greatly effects the reaction rate so I took care to try and fine marble chips roughly the same size. Another variable I am taking into account is temperature, however, I cannot control the room temperature. I would therefore have to assume that the room temperature remained constant for the duration of the experiment. As I am purposely changing the concentration of the acid, I don't need to worry about it remaining constant throughout the experiment. Also, as I will not be adding a catalyst, there should be no reason for this to affect the fairness of the experiment.
I also had to take into consideration the safety aspects of the experiment.
I will wear safety goggles throughout the experiment.
I will be careful not to spill any acid, but would take care beforehand that nothing was near the experiment that could cause an accident or be damaged if I did spill the acid.
I will be careful with all glassware in case it breaks, and if it does I will make sure it is immediately cleaned up. As I am using boiling tube racks, the risk of glass breaking is made smaller.
I will be careful with the more concentrated acids especially as it is corrosive, so I will be careful not to spill it on myself, especially in my eyes. This is why I will be wearing safety goggles at all times.
After having decided how to approach all of the variables in the experiment, I decide to carry it out. Before the experiment, I predicted that the solution with the highest concentration of acid will have a much faster reaction rate than the more dilute solutions. I have predicted this from my knowledge of the collision theory and from the results of previous experiments. I think that this will happen because the more hydrochloric acid in the solution, the greater the concentration and so the higher the number of particles in the solution. This means that there will be more particles colliding and more energy and so therefore a faster rate of reaction. The reason that I think that the rate of reaction will increase is because the reaction is an exothermic one, and this means that it will give itself more energy and therefore more collisions and faster collisions.
Therefore, I predict that the rate of reaction will increase as the concentration of hydrochloric acid in the solution increases.
Obtaining Evidence
Results:
For 10cm³ of hydrochloric acid, 0cm³ of water:
time (s)
gas collected (cm³)
0
25
20
52
30
73
40
90
50
96
60
00
For 8cm³ of hydrochloric acid, 2cm³ of water:
time (s)
gas collected (cm³)
0
4
20
34
30
48
40
63
50
75
60
84
For 6cm³ of hydrochloric acid, 4cm³ of water:
time (s)
gas collected (cm³)
0
6
20
8
30
29
40
38
50
47
60
54
For 4cm³ of hydrochloric acid, 6cm³ of water:
time (s)
gas collected (cm³)
0
3
20
9
30
5
40
21
50
26
60
30
For 2cm³ of hydrochloric acid, 8cm³ of water:
time (s)
gas collected (cm³)
0
20
2
30
2.5
40
3
50
4.5
60
6
For 0cm³ of hydrochloric acid, 10cm³ of water:
time (s)
gas collected (cm³)
0
20
30
40
50
60
Analysing the Results and Conclusions
From looking at my results and graphs, I am able to conclude that the more concentrated the solution, the faster the reaction occurred. There was a dramatic change in the amount of gas collected as more water was added to the solutions to make them more dilute. For example, if you look a graph (a), it shows how much more gas is collected with 10cm³ acid compared to the amount of gas collected with 0cm³ acid.
From looking at my results, I can also see that as the time increases, the rate of reaction decreases and as the volume of acid in the solution increases, the time of the reaction decreases.
From my results, I also plotted the moles of the solution against time and found that as time increases, the moles of the solution decreases, i.e. as the moles of the solution increases, the reaction time decreases.
All of these I had predicted in my hypothesis and had learned about when researching the collision theory, therefore, from my results I can see that my predictions were correct and fit the theory.
At this point, I was able to answer the main hypothesis, which was 'How does changing the concentration of acid affect the rate of reaction between hydrochloric acid and calcium carbonate?' The answer to this would be that changing the concentration of the acid will either increase the rate of reaction or decrease it, and so would therefore increase or decrease the amount of gas produced in the reaction, depending on whether the acid was more concentrated or diluted. These factors affect the number of collisions of reactant particles, and this in turn effects the rate of the reaction. If the number of collisions per second increases, then the rate of the reaction will increase.
If a solution is more concentrated, then there are more reactant particles per set volume. This makes collisions between the reactant particles more likely. Therefore there will be more collisions per second, so more particles reacting per second, i.e. the rate of the reaction is increased.
Overall, I think this was a very successful experiment and everything went smoothly, which is why my results are very good, and from this I am able to make a conclusion.
Evaluation
I feel that this was a successful experiment. My results seem to indicate a clear pattern from which I was able to draw a sensible conclusion. This conclusion confirmed my hypothesis. The method produced results accurately and quickly enough to complete the experiment in the hour that we had.
My results are reliable as I made sure that the experiment was as fair a test as possible. I ensured this by keeping all of the variables not involved in the experiment constant. These were the presence of catalysts and the starting temperature of the reactants. I could not control the temperature at any time in the reaction, except for a 0 seconds. This is because the reaction was exothermic and so released heat, which I could not control.
The only problem with my method was that I had to drop the marble chips into the acid, place the bung in the mouth of the filter tube and then start time. However, as this is a relatively long sequence of events to complete in the time it takes for the marble chips to hit the surface of the solution. There is a potential error. I think that one explanation for any points which didn't fit very well could be that I did not start time at the exact same point in each experiment as I could have had trouble putting the bung in the filter tube in one of the experiments but not in another one, so would therefore have started time after the reaction had already started.
Another change I would make is maybe, instead of using filter tubes, I would use a conical flask as then I would not need to use boiling tube holders, and also as it has a wider base it is more stable so could reduce the risk of accidents occurring from acid spillage's. It would then also be easier to place on a balance with a solution inside it as I would need to do for any further experiments.
To provide more evidence for my investigation, I could use a thermometer to measure the temperature during the experiment at the same regular intervals as I measure the amount of gas produced (every 10 seconds for 1 minute). This would show whether my theory of the lower concentration not heating up the reactants is true or not. For further investigation, I could use stronger acid to se if there is a limit to how quickly the reaction can take place. Also, I could measure the mass loss of the reaction by weighing the mass of the filter tube on the balance. I could take away the mass at regular intervals from the original and find out how quickly the reaction takes place.
Claire Ainscow
Chemistry coursework - Rates of Reaction
