I predict that for each of my experiments carried out that the graph will look something like this. I think that the smaller the particle size the quicker the reaction will happen and therefore the higher the line will rise in a shorter time span. To be able to compare my results and test my theory I will but all of the averages for powder, small, medium, large, and extra large, all on one graph so that I can clearly analyse the correlation. This will help me to see if particle size does affect the rate of reaction.
Also, so that my data can be recorded and collected as efficiently as possible I will record it in a table like the one shown below, this will ensure that all my results are recorded correctly and quickly, as there is only a 10 second gap between each figure recorded in which the calculations can be written down.
Fair test: To make sure that my results are accurate I will keep all variables the same except the particle size. To do this I will use the same volume and concentration of hydrochloric acid throughout and will also keep the mass of the particle sizes the same throughout. I will also use the same scales while doing my experiment so that no faulty mass is calculated making my experiment unfair to extend on this further I will make sure all my equipment is the same throughout my experiment. I will also need to make sure that I do not stir the conical flask while the gas is coming out as this will speed up the reaction making my results inaccurate. Finally, I will repeat each particle size experiment three times and find the overall average to ensure my results are correct.
Safety: To make sure that my experiment is entirely safe I will need to make sure I consider the following things; firstly I will have to make sure that I am wearing the correct safety equipment such as goggles, lab coat, long hair tired back, etc. Secondly, I will need to make sure I mix the right quantities of chemicals so that I do not cause too large a reaction which could lead to breakage or spillage; however if a spillage or breakage does occur I will need to inform a teacher immediately. Thirdly, I will need to keep all hazardous chemicals away from eyes, open flames, etc, and to prevent any irritation wash hands after the experiment is complete. Finally, I will need to dispose of the chemical appropriately and as safely as possible.
Preliminary experiment: After carrying out one preliminary test I was able to see that the previous quantities of hydrochloric acid were too large. This is because after adding the 10cm of hydrochloric acid the rate of the reaction went so quickly we were unable to record the results in a period of 10 seconds. Due to this I had to change the amount of hydrochloric acid to 5cm and to ensure that the rate of reaction was still not too fast decided to record results every 20 seconds instead.
Results:
After collecting my results and finding the overall average I recorded each of the averages onto a graph. This enabled me to compare the correlation between the different particle sizes. From this experiment I hope to see what further improvements could be made to my experiment, for example other factors that affect the rate of reaction which I may not have realised while carrying out my experiment. After analysing my preliminary experiment I can then go on to develop and improve my experiment so that my final set of results are as accurate as possible. My preliminary graph is shown on the following page;
Analysis of preliminary graph: From the graph I can see that particle size does affect the rate of reaction. However, my preliminary experiment also showed me some improvements that could be made to make my results more accurate. Firstly, when adding the mixture into the conical flask I need to make sure that it is on a flat surface, this is because that some of the experiments, as I was putting the chemical in, got shaken/ stirred. The rate of reaction can be increased if the movement of the reactants is increased as a result of stirring. This meant that my results where unfair as I was changing more than one variable each time. Furthermore as only some of the reactions were stirred some of my results became uneven as by giving the reaction mixture a stir it created jumps in the graph in which the reaction suddenly sped up overall making my results inaccurate. I also learnt that the previous quantities of hydrochloric acid and time in seconds where unreasonable, as the reaction went too fast due to too much hydrochloric acid and the 10 seconds time spans which left us with no time to record results. In my actual experiment I will only include 5cm of hydrochloric acid and record my results every 10 seconds. Finally, I learnt that each person should have a specific duty, for example one person in your group puts on the delivery tube bung meanwhile another starts the stop watch; This allows the experiment to run as efficiently as possible and means the results are far more accurate as gas is collected as soon as it is given off.
Results:
Analysis: After looking at the graphs I can see that the reaction is not constant; it is fastest at the start when the reactants are at a maximum, I can tell this from the gradient of the line. The gradient becomes progressively less as reactants are used up and the reaction slows down. Finally, the graph levels out when one of the reactants is used up and the reaction stops. From the graph I can see that the smaller the particle the faster the reaction for example the powder at 20 seconds had given off an average of 38cm3 of gas compared to the extra large which had only given off 15cm3 of gas. This proves my prediction was correct. Below is a graph showing the stages of the reaction and how it affects the correlation.
In the reaction the calcium Carbonate reacts with the hydrochloric acid, giving off carbon dioxide gas; the equation is shown below:
Although the mass of the calcium carbonate stayed the same throughout the experiment the rate of reaction increased depending on the particle size. This is because acid particles can only collide with the carbonate particles when the carbonate particles are exposed on the surface of a piece of marble. Breaking up a solid exposes more and more of the surface area and so makes the reaction go faster.
Conclusion: In conclusion this experiment has enabled me to see that my previous prediction was correct and that the smaller the particle size the faster the reaction. Overall my results are fairly accurate; the correlation between the five lines supports my prediction as the smaller the particle size the larger the quantity of gas is given off in a shorter time. This can be seen on my graph. Below are the four main factors which I believe affect the rate of reaction:
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The concentration of the substances reacting - If the of a dissolved reactant is increased, or the pressure of a reacting gas is increased, there are more reactant particles in the same volume. The more reactant particles there are, the greater the chance of them colliding. There are more collisions, so the rate of reaction increases.
- The temperature - If the temperature is increased the reactant particles move more quickly. In addition, more particles have the activation energy. The particles collide more often and more of the collisions result in a reaction, so the rate of reaction increases.
- The size of the particles - If a solid reactant is broken into small pieces or ground into a powder, its surface area is increased. More particles are exposed to the other reactant. The reactant particles collide more often and so the rate of reaction increases.
- A catalyst being present - Catalysts increase the rate of reaction without being used up. They do this by lowering the activation energy needed. With a catalyst, more collisions result in a reaction, so the rate of reaction increases.
Evaluation: Overall my experiment was fairly successful. Most of my results where reasonably accurate and allowed me to see enough evidence to conclude that particle size does affect the rate of reaction.
From my experiment I have learnt that there are many other factors which affect the rate of reaction, for example stirring the mixture; I know this as some of my anomalies results in my preliminary experiment were due to this factor. I was then able to develop on this to get more accurate results. However there are still some anomalies in the results, for example powder at 120 seconds increases to 69 which is a far greater gap then there should be as by now the reaction should be slowing down.
If I was to do the experiment again there are still some factors of the experiment which I would change. Firstly, I would continue to do the experiment until 200 seconds had passed; this is because on the graph I was unable to see the whole reaction, as I only started to see the reaction slow down towards the very end and never actually got to see the entire curve at the point where it levels out. I would also make sure that all factors were the same such as heat and stirring etc.
I could also do the experiment a different way by measuring how quickly one of the products in the experiment disappeared. I would do this by placing the calcium carbonate and hydrochloric acid in an open beaker. I would then place the beaker on some scales. As the carbon dioxide gas is produced and escapes into the air the total mass remaining in the beaker will go down. If I measured how much mass is lost in a given time I could work out the rate of reaction. Basing this experiment on my previous experiment I believe the graph would look something like this:
In conclusion I now know that the particle size does affect the rate of reaction as the smaller the particle size the larger the surface area is. With a larger surface area more particles are exposed to the other reactant, the reactant particles therefore collide more often and so the rate of reaction increases.