The rate of reaction when different concentrations
I am investigating how the rate of reaction differs when we change the concentration of Hydrochloric Acid whilst reacting with Magnesium. The rate of reaction is explained by the Collision Theory. This theory explains how various factors affect the reaction rates and how chemical reactions occur. The 4 factors of the Collision Theory are: •Temperature •Concentration •Surface area •Catalyst I am investigating how different concentrations of acids affect the rate of reaction. However I must control the temperature, surface area and catalyst by keeping them the same throughout the experiment.
I used 5 different concentrations of acid. These were, 2. 0(mol), 1. 6(mol), 1. 2(mol), 0. 8(mol) and 0. 4(mol). The reason I used such a variety of acids was to make sure my results were more reliable and to ensure I got wider range of results. I kept the temperature at room temperature and the surface area of the solution always added up to 40cm3. The magnesium was cut to 4cm each time I did the test. I kept these three factors the same to make it a fair test and to ensure my results were more reliable. I didn’t use a catalyst as it speeds up a reaction and my reaction was fast enough without using it.
I used a wide variety of different concentrations so I was able to see what effect it had on the rate of reaction. It also showed a positive correlation on my graph which helped me interpret my results. I did a preliminary test (practice test) to see how we would construct each experiment and who would do what jobs, for example marking the gas produced or timing every two seconds of the reaction. It also helped me to find out how many seconds I should mark the amount of gas produced. I started off with 4 seconds but for the 2.
0(mol) concentration the reaction was fast, so I marked every two seconds instead to get a more reliable result. Doing the preliminary test help make my final experiment more accurate and reliable. To ensure my results were reliable I repeated each test three times which helped me identify any outliers and if I had any I did the test again. This also made my results more accurate. For this experiment I used the following: •A conical flask •A gas syringe •A measuring cylinder •A rubber bung •A stop clock •Magnesium •Stand and clamp •Hydrochloric Acid •Ruler.
•Scissors •Black marker •Water I used a conical flask which contained the solution of acid and Magnesium, a gas syringe to measure the amount of gas produced a measuring cylinder to measure the correct amount of water and acid. I used a rubber bung to trap the gas produced and a delivery tube which was attached to the rubber bung that collected the gas. The gas travelled through the delivery tube and was collected in the gas syringe and I then marked off the amount of gas collected every two seconds. I used scissors to cut the 4cm of Magnesium. Collecting Data.
When collecting my data I came across some anomalous results (outliers). When this happened we repeated the test again to discard the previous outliers and get our results more accurate as we might have marked the amount of gas produced wrong. I came across many problems when collecting my results. One of many being on time and accurate when taking the readings of the amount of gas produced every two seconds. This was a problem for me as two seconds went very quickly and the gas produced was increasing rapidly, making it harder to mark the amount accurately.
Another problem was putting the bung on the conical flask immediately. It was important to do this as my results would have been affected if any gas escaped. Interpreting Data My graph shows that the higher the concentration of acid the faster the reaction. I also calculated the gradient and this shows that my highest gradient was 2. 0(mol) which was 7. 14. This was higher than 1. 6(mol) which was 5. 1. 6(mol) was higher than 1. 2(mol) which was 3. This was higher than 0. 8(mol) which was 1. 79. Finally, 0. 8(mol) was higher than 0. 4(mol) which was 1.
This shows that the gradient line gets steeper as the concentration of acid was increased. My error bars show the three different results I got each time I did the test, including my average. My error bars are high on 2. 0(mol) results. This shows that my results are not 100 % reliable and my measurements of the amount of gas produced could have been wrong or the length of Magnesium cut may have been either longer or shorter than 4cm. Apart from some of the 2. 0(mol) error bars, the rest of my results look reliable as my error bars are small.
My results show the pattern that the higher the concentration of acid the faster the rate of reaction. Overall, I think my results are fairly reliable although my error bars are big on my 2. 0(mol) and 1. 6(mol) results. This may be because I didn’t mark the amount of gas accurately on the gas syringe. Another problem could be measuring out the correct amount of acid and/or water each time I repeated the test. My results make it harder to write a conclusion as some of my error bars are big so not all of my results may be reliable.
This means my conclusion will not be 100% accurate and true. It is hard to write a conclusion as it is based on only my experiment and results and not other experiments. Since my results are unreliable it will then make my conclusion unreliable too. I have come to the conclusion that the higher the concentration of Hydrochloric Acid (for example 2. 0(mol)), the quicker the rate of reaction. 0. 4(mol) (lowest concentration) would have a slower rate of reaction compared to 2. 0(mol) as it is less concentrated.
The concentration of acid affects the rate of reaction as the lower the concentration the fewer collisions and the higher the concentration the more collisions. This is called the Collision Theory. The gradient lines also link to my conclusion as you can see on my graph that the gradient lines get steeper the higher the concentration. For example: 2. 0(mol) > (20-0) ? (2. 8-0) = 7. 14 1. 6(mol) > (15-0) ? (3-0) = 5 1. 2(mol) > (6-0) ? (2-0) = 3 0. 8(mol) > (5-0) ? (2. 8-0) = 1. 79 0. 4(mol) > (2-0) ? (2-0) = 1 As you can see from my results the number gets higher as the concentration of acid increases.
This shows how steep each line is, and that the steeper the line is the faster the reaction. Evaluation Method One of many problems I had whilst carrying out this experiment was marking the amount of gas that was produced on the gas syringe. This was difficult as two seconds went very quickly and the gas was being produced at a fast rate, so marking it on the gas syringe was hard and was not always 100% accurate. This makes my results unreliable. Another problem I had was putting the rubber bung on the conical flask as soon as the magnesium was dropped into the solution.
It was vitally important that the bung was placed on immediately to ensure no gas escaped as this would have affected our results and made them unreliable. To improve my method I could use more accurate measuring cylinders that go up in a scale of 1, 2, 3, 4 etc. so I could measure the acid and water more accurately. This would make my results more accurate and reliable. I could also use more high tech equipment that could stop the gas escaping at the start of the reaction. Using a thinner marker would also help make my results more accurate as I would be able to mark the amount of gas produced more accurately on the line.
To improve my method further I could also use a set temperature water bath which will keep a constant temperature throughout my experiment, which will then make my results more accurate. Data Overall I think my results were reliable as I repeated each test three times to ensure my results were near enough the same each time. I also used the same equipment throughout my experiment which made my results accurate as everything was kept the same. I also cleaned the conical flask after each experiment to ensure there was no unwanted solution left in it from the previous experiment.
This made my results more reliable as there was no extra solution left inside that would have made my solution more than 40cm3. I have a small outlier in my results for 1. 2(mol). This could be because I waited more than two seconds to mark off the gas produced or maybe I didn’t mark the gas syringe accurately as the black marker was thick so it made it harder to mark the correct line so this could have easily happened. I do not think all of my results are reliable as my error bars for 2. 0(mol) are big at 4, 14, 16, 18 and 20 seconds. I also have big error bars in my results for 1.
6(mol) at 6, 8, 10 and 12 seconds. Having big error bars show that my results may not be 100% reliable as I did not get the same result each time I repeated the test. You can see in my results that the higher the concentration the bigger the error bars are. There is a real difference between each of my results as one line is very steep and another is very shallow. My lines do not overlap with one another and you can see a clear difference between each line of my results. You can also see this difference in the gradient lines as the higher the concentration the steeper lines. Conclusion
I am very sure about my conclusion as my results graph show clear lines that indicate the speed of the reaction is quicker when the concentration of Hydrochloric Acid is higher. I can see this as the lines get steeper as the concentrations increases. Although my results have a few big error bars, and some parts of my method went wrong, such as marking the gas produced and putting the rubber bung on the conical flask immediately, overall I believe that my conclusion is reliable as nothing big happened that affected my results so much that I could not see the difference in the rate of reaction and come to any sort of conclusion.
My graph still shows me that there is a clear difference between the rate of reaction and the concentration of acid. I do not believe that I need to do any further experiments to be sure about my conclusion, as I am able to interpret my results and come to a conclusion that shows a correlation between my results. If I was to do my experiment again I would check the gas syringes were working and were able to move easily. I would also use a longer length of magnesium to make my reaction go further.