Below are the results of my preliminary work:
The results that I have obtained are appropriate and the time taken steadily increases without any anomalies. Thus, the method demonstrated above will be the one I will use in the actual practical
Range of measurements:
My preliminary helped affirm the range of measurements that I was going to use. I am going to vary the concentration of hydrochloric acid to 5 different concentrations. I will do this like I mentioned before by taking 10cm³ of hydrochloric acid away each time and replacing it with water. Making sure that the total volume is 50cm³ at all times to make it a more fair and accurate method. The variation in the concentrations can also be written as percentages:
100%= 50 cm³ hydrochloric acid
80% = 40 cm³ hydrochloric acid and 10 cm³ water
60%= 30 cm³ hydrochloric acid and 20 cm³ water
40%= 20 cm³ hydrochloric acid and 30 cm³ water
20%= 10 cm³ hydrochloric acid and 40 cm³ water
Fair testing:
To further ensure that the method that I was going to use was fair, I carried out the preceding precautions.
Firstly, even before the experiment is started I will rinse all the equipment to remove any previous stains that would effect the reaction. I will then ensure that the same individuals will be doing the same job. For example the same person will be timing or the same person will be measuring the gas collected each time. When taking the reading of how much gas is collected I will ensure that I read it from the bottom of the meniscus at horizontal level with the eyes, and a white background to eliminate shadow to minimize human error. When weighing the marble chips I will remember to always make sure that the weighing scale reads zero before weighing it (zero-errors.)
Moreover, the apparatus at all times will be the same. The reactants and the measuring cylinder that are used to measure the reactants will be kept separate so measurements can be taken accurately. When experimenting I will ensure that the reactants are not stirred beforehand to prevent unwanted collisions which may inadvertently speed up the reaction.
The temperature where the experiment is taking place will always be 24°C by placing it on a Bunsen burner. This is because if the temperature is increased the particles would have more activation energy and successfully collide causing the solution to react causing the rate of reaction to increase.
Also the experiment will take place directly under the light of the lab lights, so that the sun light or any dimming of light will not affect the experiment. Light intensity is an important factor to keep constant because the greater the intensity of the light the more frequently it will break up the particles into smaller particles making it more reactive then the original particles
Furthermore, the surface area is another variable that is going to remain constant so that the experiment is fair. Also there will be no catalyst added to the experiment as the catalyst lowers the activation energy making it easier for the particles to react so they have enough energy. The only variable that I am going to change is concentration as this is part of what I am trying to investigate
In addition I will ensure that the experiment will be repeated at least 3 times and then it the results will be averaged to improve the credibility. The repeat results will hopefully iron out any anomalies and give a good summary of the result of the experiment.
Safety:
My experiment will be done under supervision and done safely in order to have an efficient and productive experiment. The subsequent are the safety precautions I will take:
At all times I will be wearing goggles even if I have glasses on because acid is harmful if it gets into the eyes and possibly go in through the side of my glasses. I will also handle acid carefully because it causes irritation to the skin. Having long hair, I will ensure to tie it back at all times. I shall not taste any of the chemicals and make sure to throw the lime stones in the bin and not in the sink as they will cause it to clog. In addition, I will not run around incase I bump into anything. I shall make sure to wipe any spills rapidly to prevent accidents from occurring. If a breakage of any of the equipment occurs I will immediately inform the teacher. Incase my skin starts becoming irritated I will also report it to the teacher.
Secondary sources used:
2 GCSE Chemistry textbooks – 1) Chemistry for you by Colin Johnson
2) Chemistry for you by Lawrie Ryan
The Internet
Mrs. O’Hanlon’s lessons
The above mentioned sources were guidance in writing about the particle collision theory.
Obtaining evidence:
After carrying out the practical on the next page are the results I obtained tabulated: The acid concentration is the independent variable and the gas collected is the dependent variable.
I had obtained the averaged results from this formula:
Average result = first result + second result + third result
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On the furthest right column of the tables are my results averaged.
I tabulated rate of reaction x 1000 because the numbers would be too small to plot and a pattern can be seen more easily:
The (I), (II), (III) and (IV) are roman numerals that I used to symbolize the repeated experiment. For example (I) stands for the first trial of the experiment that I took. For the second table I figured out rate of reaction by dividing the time taken for 30cm³ to be collected by one.
Analyzing evidence & drawing conclusion:
Below I have graphed the tabulated results:
Conclusion:
Using the graphs with lines of best fit, I can draw a conclusion from my experiment:
Firstly, I can see that with the time graphs, that plot temperature against time taken for the reaction to take place, has a negative correlation. Meaning, that as the concentration increases, the time taken for the reaction to take place decreases. For example when the concentration was 10cm3 the reaction time was 63.2 seconds, but at 50cm3 the reaction time was 7 times less (9.50s.). Therefore I can conclude that my predictive statement that the concentration is directly proportional to the rate of reaction as there is a constant increase in both variables is supported by this practical.
On the other hand, the graph plotting rate against concentration has a positive correlation so the rate of reaction increases. This is because solutions of reacting particle become more concentrated because there are more particles per unit volume. Therefore they will collide more often successfully and with more energy. This supports my hypothesis that as the concentration increases (because the time taken decreases) the rate of reaction in turn increases.
Diagram:
I predicted that if I doubled the concentration, then the rate of reaction would double. My results and graph have verified my prediction.
40% concentration of acid = 34.4 seconds (rate of reaction x 1000)
20% concentration of acid = 15.8 seconds (rate of reaction x 1000)
When the 20 percentage of the concentration is doubled to 40, the rate of reaction is roughly doubled as well. This is because the solution of the reacting particles has become more concentrated as there are more particles per unit volume. Therefore they will collide more often and successfully.
In addition, the rate of reaction does not stay constant. This is illustrated in the graph Acid Concentration vs. Time taken to collect 30cm³ carbon dioxide gas.
It is the greatest at the start as this is where the gradient is the steepest showing that the rate of reaction is increasing steadily. The horizontal line illustrates that the reaction is finished because the reactants are no longer reacting so no carbon dioxide is given off. This is because the longer the reaction takes place the more of the reaction react leaving fewer molecules with less chance of reacting. If the graph is extrapolated then the horizontal line would continue to be a horizontal line. I also observed that the variation of the time taken is less between 30cm³ and 50cm³ concentrations than the 10cm³ till 30cm³ variations.
Evaluation
Overall the experiment was satisfactory however I cam across some difficulty. Firstly, experimental error beyond my control was induced as the plastic measuring cylinders used to measure the liquids volume were mass produced so they were not 100% accurate. A glass pipette should have been used as they are hand made and much more precise. The substances we used were made from stock solutions which are made fresh every lesson, therefore the concentration of these substances changed slightly from day to day during the experiment.
The equipment was rinsed with tap water which contains many impurities which may have contaminated or changed the concentration of the liquids. Distilled water should have been used instead as it is pure. In addition, using the stop watch affected the results due to human error causing the points not to be aligned on the graph so the line of best bit had to be drawn.
Furthermore, from my results I only came across one anomalous result. It didn’t fit in with the rest of the results affecting the average. This occurred when I was using 40cm³ acid concentrations (100%) I had got a time of 48 seconds. The reason behind this difference was because I had forgotten to add the water. So I repeated the result and replaced the anomalous result for the new result: 55 seconds. From then on I made sure not to forget to add water by always double checking that I had added water and then checking the volume.
If I were to repeat the experiment I would use a syringe because some carbon dioxide gas is soluble. Hence, I was not measuring all the carbon dioxide being produced. In addition I would use a SIV instead of weighing scales to accurately measure the surface area and the size of the marble chips. I would also make sure that the experiment would be performed in a single day so the temperature remains constant and that the solution used is the same being used through the entire experiment. I would also increase the number of tests and increase the amount of calcium carbonate so the reaction can slow down and allow for more accurate reading of the results to be taken to decrease the number of anomalous results and human error.
This experiment provides only presents one example so it does not verify my hypothesis it only supports it. To confirm it I would have to do numerous test and use a much more wider range of results.
To extend my investigation I would experiment using other variables such as, surface area, temperature, pressure for gas, and a presence of a catalyst. These variables would hopefully prove that they all help speed up a chemical reaction.