A metal and an acid - Sample Essay
If you increase the number of particles in the solution it is more likely that they will collide more often. In the reaction, when the magnesium contacted the acid, it fizzed and produced bubbles. The activation energy of a particle increases with heat, and the particles that have the activation energy are those particles, which are moving. In the case of magnesium and hydrochloric acid, it is the hydrochloric acid particles that have the activation energy because they are the particles that are moving and bombarding the magnesium particles to produce magnesium chloride.
Overall, I experimented 6 different molars of hydrochloric acid. The lowest molar concentration, 0. 4M, produced the least amount of hydrogen. However, rather than 1. 4M, which is the highest molar I tested, 1. 2M produced the most hydrogen in 100 seconds (explained further in evaluation. ) With the help of this graph I drew another graph to see if I could prove my prediction further. I have estimated the rates of reaction (cm3 / sec. ) with a gradient. I did this by finding the steepest part of the line between 2 points, and drawing a triangle (considering the line is straight.)
I then did the following sum: Vertical value – horizontal value = gradient = rate of reaction (cm3 / sec. ) Hee are the following calculations: Concentration (molar) Rate of reaction (cm3 / sec. ) 0Using these particular results, I have drawn another graph showing the relationship between concentration and rate of reaction. From the results in the table and the graph we can see a steady increase in the rate of reaction as the concentration of the acid increases also (positive correlation best fit line.)
This complies with my prediction. The graph shows that there is an increase in the rate of reaction as the concentration increases because the graph has it’s largest gradient or it is steepest at this point. However, there are 2 anomalous results at the end that do not meet the best-fit line. This graph could be wrong because of inaccurate results. We can also see from the rate of reaction graph that when the concentration roughly doubles, the rate of the reaction does not double; 1. 0. 4M – 0. 05 cm3 / sec. 0. 8 M – 0. 25 cm3 / sec. 2. 0. 6 M – 0. 15 cm3 / sec. 1. 2M – 1. 70 cm3 / sec. EVALUATION:
In my original prediction (planning), I predicted the following statement ‘As the concentration increases, the rate of reaction will increase also. Therefore, the rate of reaction is faster due to these collisions and if I double a certain molar, the rate of reaction will also double. ‘ According to my results and graphs, to a certain extent my prediction was correct. As the concentration increased, the rate of reaction also increased. The amount of hydrogen also increased. However, for 1. 2M and 1. 4M I experienced a few problems. They were anomalous results and did not fit the best-fit line.
1. 2M also happened to produce a faster rate of reaction than 1. 4M according to my results. To ensure that my results were not even more inaccurate for the hydrogen produced, I have drawn on error bars for the first 2 concentrations (0. 4M and 0. 6M, see graph number 1. ) For both molar strengths, at first the error bars are very close together, but as the time increases the error bars become further apart. There are a few reasons why this may have occurred; -I accidentally confused my results for 1. 2M with 1. 4M -As I recorded my results for 0. 4M to 1. 0M in one week, and my results for 1.
2 to 1. 4M the process of the experiment may have differed slightly. -Generally, the process may have changed, e. g. the bung may have been placed in the conical flask at different times. -The ribbons of magnesium may have been slightly different lengths. – When the reaction takes place bubbles of H2 are given off, which might stay around the magnesium, which therefore reduces the surface area of the magnesium and so the acid cannot react properly so this affects the results. -The time in which I swirled the magnesium in the hydrochloric acid may have differed.
If I were to repeat the experiment I would make a few alterations to the process to ensure more accurate results. The first modification would be to take readings over a wider range. For example, I would use the range 0. 0M to 2M. This would help me produce better graphs to analyse. The second change would be to take 5 repeats rather than 3, as I feel it would also help me produce more accurate results. This is because if there were any irregular results that I had not noticed or had simply produced, the averages would not be affected as much.
I would also use a pencil to measure the magnesium ribbon, as I think that even the smallest difference in millimetres would make a variance. Finally, I would measure the amount of time that I swirl the magnesium ribbon in the hydrochloric acid so that the results are fair each time. If this process was carried out correctly, I predict the same statement as my original one. I would also predict that if the concentration was doubled, then the reaction rate would also double. GCSE CHEMISTRY COURSEWORK Moe Shimizu 11G.