My results are shown in table 4 and fig5. From table 4 we can see that for the 2M concentration the first 30second produced 1cm3 of hydrogen from 0.5 to 1min (rate of 0. 03cm3/second) 3. 5cm3 of hydrogen was produced in the following 30seconds (0. 12cm3/second) the next 30seconds produced 4. 5 cm3 (0. 15cm/second) and then 6cm3 (0. 2cm3/second) and the highest which was 16cm3 produced from 3. 5 to 4mins(0. 53cm3/second).
There seemed to be a problem in the production of gas because only 6. 5cm3 was produced between 3 and 3. 5mins. For the 4M solution, the first 30 seconds produced a greater amount of hydrogen at 6cm3 (0. 2cm3/second) in the following 30seconds 12cm3 was produced (0. 4cm3/second) in the next 30 seconds between 1 and 1.
5mins 22cm3 was produced (0. 73cm3/second). Between 2 and 2. 5mins 27cm3 was produced (0. 9cm3/second. ) After 2. 5mins I could no longer take any readings because the measuring cylinder had been filled with hydrogen. The results show that for both 2M and 4M the production starts off slowly and then increases in rate. This does not support my prediction. I will need to explain why this is in my evaluation. The graph also shows that the 4M solution produces more hydrogen and at a faster rate than the 2M this is shown by the slope and height of the graphs for the two solution. Section 8, Evaluation.
In order to evaluate my work, I looked at the methods and techniques I used, the quality of data I collected and the results I obtained. There were a number of issues which affected the accuracy of my experiments. I was investigating concentration and tried to keep all other factors constant. Unfortunately this was not always possible. I kept the mass of zinc constant at 2grams but I could not keep the surface area the same for each test. This would affect the results. Another factor with the zinc was the impurities formed on the surface which would delay the reaction with the sulphuric acid.
I tried to clean the zinc with sandpaper, but it was not always available. Another factor that I had to keep constant was the temperature; again there were problems, as my results tables show. In my first experiment, the temperature at the beginning ranged from 19i?? C 21i?? C and this would have affected the time taken to produce 50cm. in the second experiment, to see how the rate of reaction changes, I had to discount the third reading for 2M because the temperature was significantly low (21 i?? C).
Even though I ignored the high temperature, there were still differences in temperatures at the start of the experiment and this would have affected the rates of reaction and results I obtained. I used a measuring cylinder to ensure I used 20 cm3 of sulphuric acid, I am confident that they were relatively accurate, however there may have been one or two cases where the amounts were wrong. There was also the possibility of human error, when looking at the amount of hydrogen produced and the time taken. My friend called out the 30second intervals while I observed the hydrogen yielded.
I tried to reduce the bias and error by taking 3 measurements for each concentration. The first prediction I made was confirmed by my results, with the higher concentration producing 50cm3 of hydrogen at the fastest rate. The second prediction about the proportional relationship was not fully supported by my results. The reason for this could be some of the problems I raised above in particular temperature and surface area of the zinc. For the third prediction I would have expected the rate of reaction to be fastest at the beginning and then to slow down as more and more zinc atoms and acid particles were used up.
My results did not confirm this because the rates were slowest at the beginning and then grew faster. This was probably because of the induction period at the beginning and the impurities on the zinc surface which could have slowed the reaction down at the beginning. I was not able to see a reduction in the rate of reaction as I expected because hydrogen was still being produced when I stopped my experiment and had failed the 100cm3 cylinder I was using, thus I would have needed more time and a bigger cylinder or a smaller amount of the zinc and sulphuric acid.
How could I improve the experiments? To achieve better results I could make sure that the surface area of the zinc was the same for each experiment by using a machine to cut out the zinc. I could also ensure that the zinc was free of impurities. I could also make sure that the experiments temperature was kept constant for each test. I could also try to minimise the human error factor of measurements of hydrogen and time by having an alarm clock to beep at specified times, and a dry board marker to mark on the levels of hydrogen produced at each time interval.
I could also use a bigger cylinder to ensure that I can carry out the experiment to the end, or alternatively I could reduce the amount of zinc used. What further tests could I do? I could carry out a test that would enable me to measure the rate of reaction until the end when the total amount of hydrogen had been produced. This would allow me to observe the falling rates of reaction as the acid and zinc were being used up. I could also see what impact additional grams of zinc would have on reaction time. I could also see how the other related factors affect the rate of reaction.
For example for surface area, I would keep the mass of zinc constant but in different forms up to powder form and see what impact this has on reaction rates. I could also look at temperature and carry out tests to see how a degrees increase impacted the rates of reaction. I could also carry out a test to investigate what impact a catalyst would have on a rate of reaction. ?? ?? ?? ?? 14 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.