By looking at the results, we realised that using magnesium granules would be too fast reacting and also be inaccurate. The syringes to be used only go up to a maximum of 100 cm3. Two measurements were taken and an average of those was used to ensure an equal result. These averages were used on the graph so that the graph would be more reliable. H2 produced every 10s (cm3) Concentration do believe that all of the results obtained are valid and they all follow the pattern of increases hydrogen production over the period. The evidence shows that the concentration of the acid does effect the rate of a chemical reaction because as the concentration of the acid decreases, so does the rate (time taken the fully react increases). As the concentration decreases by 0. 5M, the time to fully react doubles. Although this differs to the prediction, it still shows regularity toward the theory.
From the graphs, a strong pattern is deducted in which as the acid becomes more concentrated, the gradient of the initial reaction also increases. This shows that as stated in the prediction that a higher concentration shall increase the frequency of successful collisions. From this evidence, it shows that the prediction was correct in that the rate of reaction increases as the acid concentration also does. However, I did not predict the numerical increases correctly. Instead of total reaction time halving as concentration doubling (as stated in prediction). It was closer to quadrupling.
The evidence can be further processed to find the initial rate of reaction after the first 10 seconds. Rate of reaction = Ave. H2 produced in time period Time period 2. 0 Molar 1. 5 Molar 55 ( 10 = 5. 50 cm3/per second 30. 5 ( 10 = 3. 05 cm3/per second 0. 5 Molar 1. 0 Molar 17. 5 ( 10 = 1. 75 cm3/per second 2 ( 10 = 0. 20 cm3/per second Acid Concentration (Molar) Rate of reaction (cm3/per second) The results above have been also showed in the graph below. I think that procedure used was substantial and gave accurate results.
I believe that there were just two slight anomalies for the 1. 0 Molar concentration; I believe that this could have occurred due to a miss reading. However, I think that the more established explanation would be that the average was pushed higher because, in measurement 1 the reaction totally finished 20 seconds after measurement 2. Therefore, due to a higher amount of hydrogen produced, this increases the average that makes the pattern change.
Here you can see that for 1. 50M, the reaction finished in the second measurement 20 seconds before that in the first. If both measurements had finished at the same time, the average would still be proportional to the others; instead, it starts to slow too early therefore setting the results off the pattern a small amount. Although it only differs slightly from the curve it still is a bit different and would be more accurate if the experiment is repeated. To improve the procedure, I would make sure that the stopwatch is started at the exact point of impact between magnesium and hydrochloric acid.
I would accomplish this by using an electronic device that as the magnesium is released (held very close to the acid), it would start the stopwatch. I would also use an electronic gas syringe, which is data logged using a computer to improve accuracy. This equipment is advanced and may not be as available as the equipment currently been used. The reaction between Magnesium and Hydrochloric Acid is an exothermic reaction, therefore in the experiments with the more concentrated acid, the heat would increase the rate of reaction due to the particles have more kinetic energy, increasing collisions per second.
In the reactions of higher concentrations, the reaction was over within 30 seconds, whereas the lower concentrations were over in well over 2 minutes. Therefore, the higher concentration reaction had less time for that heat to dissipate out, altering the results more. Nevertheless, in the lower concentrations, the reaction took a lot more time, giving it more time for the heat to dissipate. This would not alter the results as much. Still, I do believe that the results are reliable and could be used to further other work in the same area.
On the rate of reaction graph, you would expect it to be a straight-line graph, but instead, it is a curve. This is because it is an exothermic reaction and for the higher concentrations, there are other factors effecting the results (see above). To provide additional relevant evidence, I would choose to closely investigate the reaction between Magnesium and Hydrochloric Acid at low concentrations (circled on the rates of reaction graph).
This is because these reactions are only effected very little by the exothermic heat factor. This is why the results of very low concentrations would prove to be more reliable and accurate to see the effect on different concentrations. Show preview only The above preview is unformatted text This student written piece of work is one of many that can be found in our GCSE Patterns of Behaviour section.