We chose to see how long it took to produce 15cm3 of hydrogen because, during our preliminaries, when our original measurement was 20cm3, sometimes not enough hydrogen was produced.
The measuring equipment that we used was chosen for the specific measurements that it could provide – to measure out the water and acid we used a pipette as it could easily remove or add a very small measurement to exactly make up the 20ml that was the total measurement of our acid and water solution. The technique for collecting the gas was reliable. The same person completed the same specific job in the practical which meant that the reaction times of the person with the stopwatch wasn’t different each time and one person didn’t shake the boiling tube to give the particles more energy to collide when they were placing the bung on, all of which would make the tests slightly more unreliable.
Collecting Data
We took careful care to keep any interfering factor under control throughout the practicals by recognising them during the preliminaries that we conducted. These included the exact concentration of the acid, the exact length of the magnesium, the speed with which the bung was placed on and the temperature of the room (and consequently the solution). We were able to easily control the former three with little problems but the latter was much harder to manage. The measurements were correct to the closest millilitre and milligram that was feasibly possible as we used measuring cylinders and rulers that offered the highest level of accuracy. In the preliminaries, we chose the person who was most suited to continually placing the bung on and as they were able to get a feel for the speed and the reactions that were required during the introductory experiments they were able to place it on at a consistent speed. This at least improved the reliability of the experiments. The temperature of the room was out of our control so the only thing that we were able to do was try and complete the tests in one session as the temperature wouldn’t have varied greatly. However, we were unable to do that so instead we continued the experiments on a day which was about the same temperature.
The range of our data covered 2M, which was the most that we able to do. The values tested were: 0.25M (2.5ml HCl/17.5ml H20); 0.5M (5ml HCl/15ml H20); 0.75M (7.5ml HCl/12.5ml H20); 1M (10ml HCl/ 10ml H20); 1.25M (12.5ml HCl/7.5 ml H20); 1.5M (15ml HCl/5ml H20); 1.75M (17.5 ml HCl/ 2.5ml H20) and 2M (20ml HCl). In total, we conducted twenty-four experiments as we repeated each concentration three times to ensure accuracy and reliability in the results. Also, if there were any anomalies it would have allowed us to recognise the fault almost immediately instead of only realising when we compared all the data after the practical aspect was finished. Thankfully, we did not receive any anomalies.
Interpreting Data
Our final results do indicate a specific trend relating to the rates of reaction: as the concentration of the acid became higher, the 15cm3 of hydrochloric acid was produced faster. Therefore the conclusion that I draw is that the more concentrated the acid, the quicker the reaction.
I think that this is because there are many more particles in the 2M concentration than there is in the 0.25M concentration. If there are more particles, the number of collisions that occur between the particles is higher which in turn increases the chance that they will collide with sufficient energy to react. This explains why, as the concentration became higher and the number of particles became gradually higher, the rate of reaction gradually became faster.
As there is a steady line of best fit, the conclusion is sound because there are no anomalies that would suggest that our results are unreliable.
Evaluation
Method
When we collected our data, we tried to ensure that everything was kept the same throughout the practical.
As we were measuring the 15cm3 of hydrogen by eye, some of the timing may be slightly out which could affect our overall results. However as we measured all of them by eye the results are still reliable, if slightly off of the completely precise mark. All of our equipment had measurements on that were small enough for us to measure to the exact cm3.
There are ways in which the method could be improved – instead of using a measuring cylinder to measure the amount of hydrogen, a gas syringe could be used. Also, we could perform the experiment in a temperature-measured room. This would help make the experiment more reliable as the temperature would remain consistent throughout the practical, thus reducing the interfering factors influence upon the results.
Data
There were over twenty tests conducted, three of every concentration. The amount of data that we collected was a lot and the average difference between the highest and lowest value of each concentration was 14.5 seconds. This is quite low and therefore shows that there the results are reliable as there were no anomalous results.
The techniques that I used were repeated by the same people, to the same standard as was feasibly possible which makes the technique sound. Because my results were reliable, I am confident that my conclusion is reliable.