Fair Test
To ensure that this experiment is a fair test I will make sure I keep the other factors that can affect the reaction rate the same.
By keeping the temperature the same the rate of reaction will neither increase nor decrease. If I were to alter to temperature and it rose then it would make the test unfair as there would be more frequent collisions between the particles, this would be due to the heat applying more energy to the particles. So I will try to carry the entire experiment out on the same day and it should be all at the same temperature, by doing this I will neither increase nor decrease the frequency of collisions between the acid particles and the calcium carbonate.
You can see the difference from this drawing, which was taken from Chemistry For You by Lawrie Ryan
Also to keep it a fair test I will keep the surface areas the same. This is because as we increase the surface area, we increase the rate of reaction. Due to the surface area being larger the number of particles will increase making there a greater chance of the particles colliding. To keep the surface area the same I will weigh out the exact same weight for every time I repeat my method and I will measure the length and width of the pieces.
An example of how the surface area of an object can change, taken from Chemistry For You by Lawrie Ryan
Method
First of all I will check that I have all of the equipment required on the list. Once I have made sure that everything is there and I won’t need to collect anything else later on I will set it up as I drew in the diagram. To begin with I will measure out 15ml of 1.5M strength hydrochloric acid and then pour this into the conical flask. I will then measure out 1.5g of calcium carbonate chips ensuring to make the surface areas, as close to being the same as possible. I will pour the calcium carbonate chips into the flask and put the stopper that leads to the gas syringe into the top I will start the stopwatch as well. To help me do this all at the same time I will get someone to start the stopwatch off for me at the correct time. I will take the readings of the amount of carbon dioxide collected every ten seconds for a minute. I will then take the average from the results. Once I have repeated this 5 times I will start to dilute the acid. I will take 2ml of acid away each time and replace it with distilled water. I will keep doing this until I have 5ml of acid and 10ml of water. For each one I will have 5 readings to maintain reliability.
Preliminary Work
Whilst carrying out my preliminary work I discovered that there are so many different ways to investigate the concentration factor. After using an acid of 0.2M, 0.5M, 1M and finally 2M. I did not think that the results that I was getting with these particular strengths were working well enough. They either made the reaction happen too quickly or too slowly. This was still the case when I tried all different types of calcium carbonate, from the powder to the large sized pieces. I decided to make my own 1.5M strength acid. I found out that if I used 50ml of 2M acid and 50ml of 1M acid I would have an equal quantity of acid that was 1.5M in strength. After several attempts to find out how much would be the right amount to use, I decided to use 15ml of the new 1.5M strength that I had previously made. I then decided to use 1.5g of the smallest chips of calcium carbonate as the powder reacted too quickly, not leaving me many results and the larger pieces took too long to react leaving me too many results. Although the powder helped to keep the surface area the same it just reacted too quickly. I made sure that the pieces I used of calcium carbonate were very similar in size and weight. I decided to take 6 readings, one for every 10 seconds and then repeat each one 5 times to ensure that my results would be reliable. The preliminary work was a huge help to me as it let me try out a lot of different methods rather than just the one that I originally thought would be successful.
Analysis
In doing this experiment my initial thoughts were proven to be correct: The higher the concentration, the faster the reaction. This is due to more particles in an acid of higher concentration, and of the same volume, which will cause the calcium carbonate to collide more frequently with the acid particles. As shown in the diagram below:
On the previous page the results from my experiment can be seen in the graph, which clearly shows the results at each stage as I increased the concentration levels. I think this happens because when the concentration increases there are more particles for the calcium carbonate to collide with, whereas if the concentration is more dilute there are fewer particles, so fewer collisions happen less frequently. I was pleased with the method I used although if I were to do this experiment again I would ensure that the surface area of the calcium carbonate chips were identical, which would in turn give a better set of results. This would be difficult but could be possible by using a glass-cutting tool. We used a grater to reduce the surface area though it was not effective and found to be very time consuming. If I were to use the powder form of calcium carbonate I would have to use a larger gas syringe as the gas collects too quickly leaving not enough results and quite an unreliable set.
Evaluation
I think that the method I chose to use was successful and worked well. This was because I ended up with quite a reliable set of results, which were very accessible and easy to plot onto a graph. It was very clear that the weaker the concentration, the lower the rate of reaction. Therefore if I were to double the concentration the reaction would happen twice as fast. The results in the graph
seem to be directly proportional, which was helpful as it gave me a clear line of best fit. I had no anomalous results in any of my lines on the graph and the shapes of the line show a strong positive correlation. This once again proves that my prediction was correct in saying that the higher the concentration, the faster the reaction and the more carbon dioxide is given off. A possible improvement that I could make to increase the reliability of my results would be to ensure that the calcium carbonate had exactly the same surface area every time. It would also make my results more accurate because due to the surface area being larger the number of particles will increase making there a greater chance of the particles colliding.
The results on my graph proved to be in a line of correlation because of the near accuracy. From the results collected and the fact that I repeated each concentration five times the results acquired to be reasonably reliable hence it is possible to draw a valid conclusion. I would repeat the method and have a control. I would do it once through with acid and once through with water. This would prove that it was the acid producing the carbon dioxide and not the water.
