There are other factors that affect the rate of reaction. A catalyst in a chemical reaction increases the rate of reaction. Catalysts speed up a reaction without being used themselves, and they remain unchanged. Another factor that can affect the rate of reaction is light presence, e.g. during photosynthesis light is needed for the reactions to actually take place.
Variables
To look at the effects of the factors effecting rate of reaction I will change certain variables in my experiments. For example, if I was to change one variable, then all the others must stay the same and remain constant, in order to acquire an accurate and fair set of results.
The four variables I could change are:
- Concentration of reactants
- Temperature of the water
- Catalyst used
- Surface area of reactants.
I have chosen to change the variable of temperature of the reactants. Whilst I change this variable, I know that as I carry out the experiments the other variables must remain constant. The temperatures I will investigate are 20°C, 30°C, 40°C, 50°C, 60°C, 70°C and 80°C.
The dependent variables are the variables that will change and the independent variables are the ones that have been deliberately altered by me to be a certain way and remain constant. In my experiment, the independent variables are calcium chloride, water and carbon dioxide. These variables help me to determine the rate of reaction for each test by measuring the amount of gas released. My controlled (independent) variables will stay the same in separate experiments, and if they are not kept constant then the test will not be worthwhile, as the rate of reaction would be constantly changing making my results inconclusive. Other variables that are also controlled are concentration (molar value) of acid, surface area of reactant and volume of acid used.
Prediction
I predict that the temperature will increase the rate of reaction as it increases. Therefore I predict that 80°C will be the quickest temperature with the fastest rate of reaction, and 20°C will be the slowest temperature, producing the slowest rate of reaction. This is due to that fact that as temperature rises the molecules are given more heat, resulting in them moving faster and more efficiently, and therefore providing a greater chance of collisions to form product molecules.
However, at low temperatures there is very little energy in the molecules. They barely move at all, and if they do collide it isn’t with enough energy to cause a reaction, and the molecules just bounce off each other. So if the temperature is increased then the molecules collide with more energy and therefore more speed, causing effective collision and reactions. I therefore predict that as the temperature doubles, so will the rate of reaction. I predict that temperature will have an effective force on the rate of reaction, as it has a great proportion of effective collisions and also an increased number of collisions.
Diagram
Method
- Firstly I will collect the equipment stated in the apparatus list, and set it up as shown in the diagram.
- I will then accurately measure out the chosen weight of calcium carbonate on the top pan balance and the selected volume and molar value of hydrochloric acid using a measuring cylinder (see preliminary experiments).
- I will then fill one beaker with tap water, and the larger beaker with the selected temperature of water, checking it with a thermometer to ensure it is correct.
- I will then pour the measured out hydrochloric acid into a conical flask, and place the flask into the large beaker of heated water.
- I will then add the calcium carbonate chips/powder to the acid, fit the bung on top of the conical flask and start the stopwatch immediately, measuring the volume of carbon dioxide produced every 15 seconds for 2 minutes.
- For the main experiment (not preliminary), I will repeat this procedure 3 times for each temperature, then work out an average volume of carbon dioxide produced for each temperature. However, for each repeat, I will still keep the other variables constant.
Preliminary Experiments and Results
In order to know what the optimum values will be for my independent variables, I must carry out various preliminary experiments first. The results of these experiments will help me to know how much and what types of calcium carbonate to use, what strength acid to use and how much acid to use. I am also carrying out preliminary experiments to ensure the method, apparatus and safety aspects work well for when I carry out the main experiment. Any flaws that appear in the set up of the apparatus will become clear in the preliminaries, and I will be able to put these right for the main experiment.
The first experiment I did was at 80°C, using 2g of powdered calcium carbonate and 25ml of 1 Molar acid. In this experiment, too much carbon dioxide was produced too quickly, and I was unable to obtain any results. This could have been for a number of reasons, such as the high temperature combined with too much powdered calcium carbonate.
The next experiment was done at a much lower temperature of 25°C, this time with only 1.5g of powdered calcium carbonate and 25ml of 1 Molar acid. Again, I could obtain no results as too much gas was produced too quickly. As the temperature was lower this time, the problem must lie with the calcium carbonate or the acid, with maybe too much powder with a too large surface area reacting too quickly.
For the experiment after this, I used 8.8g of calcium carbonate, but this time in the form of large chips instead of the powder, to create a smaller surface area and a slower rate of reaction so that I could obtain some results. Again, I used 25ml of 1 Molar acid. The results obtained from this experiment are on the next page.
Preliminary Experiment 3
This experiment provided a definite improvement in results, as the rate of reaction slowed down enough for me to take down results, but it was still to fast, as the gas was all being produced within the 2 minutes. The next experiment I did was using 13.3g of large chips, which worked out as roughly 10 chips, at 25°C again. I used the same volume of acid, 25ml of 1 Molar. The results were even better, more accurate and precise and giving a better idea of the rate of reaction. These are the results:
Preliminary Experiment 4
This experiment provided accurate and reliable results, with a good weight of calcium carbonate and a good volume and strength of acid. I will use these values for my independent variables in my main experiment:
Chip size/weight = 31.3g Calcium Carbonate (large chips)
Volume of Acid = 25ml Hydrochloric Acid
Strength of Acid = 1 Molar
From my preliminary results, I can see that the apparatus, method and safety aspects all worked well, and I have gained some sound independent variable amounts.
Reliability of Results
In my experiment, my results must be fair, accurate, safe and reliable, and I will have to take precautions to ensure these are achieved. Thanks to my preliminary results, I have been able to change the weight of the calcium carbonate and the volume of acid I will use for the main experiment. I have to make sure that temperature is the only variable I change, and that the other variables remain constant and accurate, e.g. the time intervals. I will repeat each test 3 times, making sure that when I average out the results, the final results are accurate with no anomalous results outstanding. I need to use averages because I could make mistakes due to me or the environment, so repeating the experiment will rectify these mistakes and enable me to smooth over any anomalous results.
Safety
To ensure my experiments are carried out smoothly and safely, I will wear protective safety goggles at all times, set up the equipment safely and handle all chemical substances with great care, washing my hands after handling them. I must also be careful when using electrical equipment, such as the kettle, near water during the experiment. I must keep my concentration throughout, to prevent harm or injury through risk or danger. Any spills or breaks must be reported to the teacher immediately, again to prevent the risk of injury or harm.
Results Temperature 20°C
Temperature 30°C
Temperature 40°C
Temperature 50°C
Temperature 60°C
Temperature 70°C
Temperature 80°C
Conclusion
From my graph, you can see that as time went on, the rate of reaction increased greatly, and more carbon dioxide was produced faster. This happened as the temperature increased, with the greatest amount of carbon dioxide produced at 80°C and the least amount of carbon dioxide produced at 20°C. This is just as I stated in my prediction.
From looking at my data I was able to work out the rate of reaction. You can see from looking at the graph that as the temperature increased, so did the rate of reaction. Again, this is just as I predicted. The rate of reaction for 80°C was 23.36 times faster than the rate of reaction for the 20°C experiment.
There is an increase in the rate of reaction when the temperature is increased because the reactants are given more energy, so they travel further with more speed, and more collisions occur with more force. This increases the chance of more effective collision, as there is a greater proportion of particles, so they have sufficient energy to overcome activation energy.
I can now conclude that increasing the temperature at which a reaction takes place increases the rate of reaction, which is greater than that of the concentration. Temperature has a greater effect on the rate of reaction than, for example, concentration. This is because increasing the concentration only increases the number of particles that can collide, which obviously causes more collisions. However, an increase in temperature gives these particles more energy and force, so they collide better, creating an increase in the proportion of effective collision, whereas increasing the concentration just increases the number of particles.
Evaluation
I believe that the results I have obtained have been greatly conclusive, accurate and reliable. I believe they are accurate and reliable as I repeated each experiment 3 times before working out an overall average. I also kept the amount of calcium carbonate and hydrochloric acid constant throughout each experiment, and I have only changed the dependent variable of temperature. My results are reliable as I have been correct in my predictions, and then gone on to back up these predictions with scientific theories and explanations, for example the collision theory.
I believe most my results were accurate, as I repeated each trial 3 times then worked out averages, although there were a few inevitable anomalous results. These were, however, unnoticeable when the averages were worked out, and as a result my results tables all contain accurate and reliable results. These anomalous results could have been caused by human error, the environment (room temperature for example) or poor timing with the stopwatch. Limitation of techniques could also have caused the anomalous results.
I think that my experiment produced accurate and reliable results, which were good enough to be conclusive. There were a few limitation and human errors to produce anomalous results, but fortunately these were kept to a minimum, and easily eradicated when averaged out. The only major problem was the speed of the reaction at 80°C, my maximum temperature. I ended up missing the last few results because the gas was produced slightly too quickly. If I did the experiment again, I would only go as high as 70°C to prevent this happening again. Unfortunately, the experiments for 70°C and 60°C became slightly anomalous in themselves, as 60°C had a faster rate of reaction than 70°C. This was most probably an error on my part, perhaps timing that was too slow or a measurement that wasn’t accurate for the 60°C or 70°C trials. The anomalous temperature, 60°C, has been highlighted in red on the first graph. Here, the line can be seen clearly overtaking the line for 70°C after 15 seconds, and the results on the 60°C are anomalous as a result. All the other lines on the graph, however, correspond with my prediction and back it up. As the temperature increases, so does the rate of reaction.
If I were to repeat the experiment again, I would work under strict environment, such as in a closed room with no winds or temperature changes. I would also try and use more accurate ways of reading the temperature and keeping the temperature constant, such as by using a water bath. Doing this would possibly make my results even more accurate. I would also try and make my timing even stricter, possibly using a smaller time interval such as 10 seconds instead of 15, to get slightly more accurate results. I may also use a larger range of acids. I only tried the 1 molar acid, but if I were to repeat the experiment again, I would perhaps use 3 and 4 molar acids and test them under high temperatures. I would like to investigate in future the effect of catalysts and surface area on the rate of reaction, to be more conclusive on the subject and widen my knowledge.
All in all, my experiment was a success. Everything went well, and I believe that the techniques and methods I used were accurate and sufficient enough to provide me with a sound set of conclusive results.
Frances Duffy 11H1
