Making sure that the mass of small marble chips is as close to 5 grams as possible.
Making sure that the concentration is always the same, and that the same amount of acid (50cmз) is measured and used each time
Results are taken precisely every 30 seconds to obtain a sensible set of results, which can either support or contradict my prediction
Ensure the equipment used is always the same
That I do not misread results
The temperature of the acid is heated accurately to ensure a consistent change of my variable
That the temperature is measured in degrees Celsius
Finally, that I ensure the environment I am working in is safe and suitable
Before obtaining my results, as part of my preliminary work, I tested the reaction between 50cm³ of HCL and 5g of CaCOз, in order to ensure it was a combination that could provide useful results.
AS my chosen variable is temperature, the five values that I will use that cover a wide range are:
I predict that the results of my experiment will conclude that the higher the temperature gets, the quicker the rate of reaction will be, so therefore more (CO²) gas will be produced within the 5 minute time limit. This will show a tight, positive correlation on my graph after I have plotted the results. I predict that my variables will affect each other in the following way:
The scientific knowledge I have that can support my prediction is based on the collision theory. This concludes that for particles to react they must collide with each other, and must collide with enough energy to guarantee that they do not just bounce off each other, but make a successful hit. Certain factors; concentration, surface area, or temperature in my case, increase the frequency of collisions, by causing the particles to vibrate more rapidly. Temperature also causes the collisions made between the particles to be more successful, which in turn increases the rate of reaction.
Obtaining Evidence
In the table below are the results I obtained during my experiment:
Analysing Results:
In order to evaluate my results correctly, I plotted my results. I also calculated the initial rate for each temperature.
After analysing the graph, it shows that the rate of reaction increases (more gas is produced) as the temperature increases. This affect between the two variables is shown in the overall pattern of the curves. Also, a more general correlation between the variables is shown in the gradient against temperature graph. As a result of this, I can conclude that the ‘Collision Theory’ is the correct scientific knowledge that proves why temperature increases the rate of reaction, therefore This theory is that for particles to react they must collide with each other, and must collide with enough energy to guarantee that they do not just bounce off each other, but make a successful hit. Certain factors; concentration, surface area, or temperature in my case, increase the frequency of collisions, by causing the particles to vibrate more rapidly. Temperature also causes the collisions
made between the particles to be more successful, which in turn increases the rate of reaction.
My Evaluation:
After observing the strong correlation between the increase of temperature and rate of reaction, I can prove that my experimental method was quite accurate, and proved to also be fair. The results were accurate as I only changed one variable (temperature) in order to see the effect it had on the rate of reaction. If I had chosen to change more than one variable in each experiment, it would have been impossible to conclude which factor affected the rate of reaction.
Although my results seem to support my conclusion, their correlation is not extremely tight. This could be because the way in which the results were taken might have been inaccurate, and caused one piece of data to become anomalous. The results that I found to be the most anomalous are that of 20°C. Reasons for this and mistakes in general might be:
This set of data was taken at room temperature, which is continually varying. This factor also affects the temperature of all the other readings
The mass of CaCOз used might have been incorrect
All the marble chips most definitely didn’t have the same surface area, which affects the rate of reaction greatly. This therefore, could be why the correlation between my results varies.
The measurement of HCL might have been inaccurate
Water in the conical flask might have affected the concentration of acid
The scales might have malfunctioned, causing the amount of CO² produced not to be recorded accurately
The stopwatch may have been started too late, therefore delaying recordings
The scales might have not been zeroed in time, or properly
Different equipment may have been used each time
The acid might not have been at the correct temperature
The human eye is not a very accurate means of recording data, as we are very likely to miss read results and timings.
If all the above factors were not accurate, then they might have affected all the results in some way, causing the experiment to become unfair. However hard one may try, errors will always occur. Ways in which my experiment could be improved to assure that errors and anomalous results are minimized is to make certain that all the factors stated above are as correct and accurate as possible.
In order for this to happen, I believe that the most accurate way of recording results, completing the experiment and preventing mistakes, is if a computer performs the experiment. This is because computers are the most accurate means of technology (much more accurate than us), at recording results and making sure that all the variables are controlled accurately. Also, it is so accurate that it would measure the acid to exactly the right temperature, as well as measuring the exact measurement of acid, and mass of marble chips. It would also make sure that all the marble chips have the same surface area (or roughly). A computer would also be able to design the most efficient and safe equipment for this experiment, to ensure that all results are recorded as suitably as possible. It would also ensure that the equipment used in each experiment is identical to the equipment in the previous, so that there would be a fair test.
However, computers are not available in schools to perform such tasks. Therefore, I believe I performed my experiment well, as my results proved my prediction and showed a strong pattern between variables. Like I said before, in order for the results to be as fair and accurate as possible, I must eliminate all mistakes stated previously.
To improve the experiment; although not necessary, I believe that taking an average of each measurement would make sure that my results are as accurate as possible, and show a tighter pattern of correlation.
Bearing in mind the results of my experiment, I can conclude, that the higher the temperature, the faster the rate of reaction. This can be proved by the fact, that every 30 seconds when I made my recordings; there was more CO² gas let off, as the temperature increased. The scientific knowledge I have that can support my conclusion on my outcome of results is based on the collision theory. This concludes that for particles to react they must collide with each other, and must collide with enough energy to guarantee that they do not just bounce off each other, but make a successful hit. Temperature is just one variable that causes the particles to vibrate more rapidly, which increases the rate of reaction by increasing the number of successful hits between vibrating particles.
