From these results I will now draw up three graphs therefore I will be able to see the anomalous results. From the pattern of the graph I will be able to see how these variables affected the process of Electrolysis.
Analysis:
This is the scientific knowledge of electrolysis in the experiment we carried out.
When dilute sulphuric acid is electrolysed using carbon electrodes, hydrogen and oxygen are obtained at the electrode. It allows 2 gases to be collected: sulphuric acid has the formula H2SO4. In water it forms ions:
2-
H+ and SO4 from sulphuric acid, H+ and OH¯ from water. The
positive ions go to the cathode (negative electrode) and the negative ions travel to the anode (positive electrode.)
At the cathode hydrogen gas bubbles off, because of this reaction:
4H+ + 4e¯ 2H2
At the anode - Hydroxide ions give up their electrons move readily than sulphate ions, so O2 and H2O are formed. The oxygen bubbles off and sulphate ions remain in the solution. The overall result is that water is decomposed rather than acid:
2H2O (l) 2H2 (g) + O2 (g)
Analysis of graph one:
The first graph tested the variable: distance between the electrodes. The pattern of my graph shows that the greater the distance between the anode and cathode, the weaker the flowing current is, and vice-versa - the shorter the distance between the electrodes the faster the current flows.
The scientific knowledge behind this is that when the electrodes are further away from each other the ions have further to travel therefore they loose energy on the way. The ions also have more water molecules in the solution to pass through if they travel a further distance. The water molecules spilt and this is what blocks up the ions from flowing. If the ions have further to travel then there will be more of these split water molecules the ions have to flow through and the ions will use up more energy doing this. As a result the current is weaker.
The results of the graph compared to my prediction are very accurate because my prediction was the same as the scientific knowledge for the results of my graph. The pattern of the graph shows that the greater the distance between the electrodes the weaker the current is.
There were one or two anomalous results on my graph and this could be due to a slight mishap during the practical experiment for example: the electrodes might have been held inaccurately therefore an unusual result would have occurred.
I come to the conclusion that the further away the electrodes are from each other, the slower the current flows and the closer the electrodes are to each other the quicker the current flows.
Analysis of graph two:
The second graph tested the variable: depth of solution. The pattern of the graph shows that the deeper the anode and cathode are in the solution, the faster the current flows and vice-versa - the shallower the electrodes are in the solution the slower the current flows.
The scientific knowledge behind this is that when the electrodes are placed deeper in the solution, the anode and cathode have larger areas where the ions can attract to. The positive ions are attracted to the cathode and the negative ions are attracted to the anode. When the electrodes are places in a shallow volume of solution there is a much smaller area where the ions can be attracted to therefore, there is a weaker current flowing.
The results from my graph are very accurate to my prediction because my prediction was the same as the scientific knowledge for the results of my graph. The pattern on my graph, which is a straight diagonal line, summarises all of the scientific explanation for this particular variable. The deeper the solution the stronger the current.
There are a few anomalous results, which might have occurred due to being inaccurate during the practical experiment, for example: Not holding the electrodes steadily in the solution and therefore an anomalous result would have occurred.
I come to the conclusion that the deeper the electrodes are in the solution, the faster the current flows and the shallower the electrodes are in the solution, the slower the current flows.
Analysis of graph three:
The third and final graph tested the variable: Concentration of solution. The pattern on the graph shows that the stronger the solution is, the faster the current flows and vice-versa - the weaker the solution, the slower the current flows.
The scientific knowledge for this is that when the solution is a stronger solution, it has less water molecules in them. When the water molecules split this slows down the movement of the ions because the water molecules block them up therefore when there are less of them this makes the current flow faster. Also the acid in the solution help the ions flow quicker so when the concentration is stronger there is more acid to help the current flow quicker.
The results on my graph are accurate to my prediction because my prediction was the same as the scientific knowledge for the results of my graph. However the pattern on the graph is difficult to work out whether the line of best fit is a straight diagonal line or if it's beginning to curve therefore I would need a wider range of values to identify this.
There are not really any anomalous results because the practical experiment was carried out quite accurately. However if an anomalous result did occur then I would speculate that it would be due to the concentration of the solutions being mixed up.
I therefore come to the conclusion that stronger the concentration of the solution is the faster the current flows and the weaker the concentration of the solution is, the slower the current flows.
Evaluation:
I am now going to evaluate the results I received from the practical experiment and say how I can improve this in the future.
To make the experiment accurate, I repeated the test three times so I could make sure I was getting accurate results. The repeats were always very similar and most of them were even the same because I used a lot of accurate equipment e.g. - an ammeter to measure the current flowing, a measuring cylinder to measure the volume of the solution, and a ruler to measure the distance between the anode and cathode. In my results, among the 3 sets of repeats, there were some different readings. To make the test accurate, I found out the average result from the three repeat readings but because there was one different reading I left it out so my average result would not look anomalous when I plotted the graph. Below is part of the table of obtaining evidence to show how I worked this out:
This anomalous result occurred due to a mishap in the practical experiment. As this result is from the experiment testing the variable: depth of solution, I therefore speculate that the electrodes were not held steadily for the duration of the reading or the electrodes were placed into a deeper solution than the one we were testing. This would have obviously effected the reading that the ammeter gave.
Overall I do think my results are reliable because most of the readings are the same or similar but I do feel that I need to be more accurate in the practical experiment to achieve repeat readings which are exactly the same.
When I came around to plotting my graphs a pattern did occur in each one however I think that a wider range of values needed to be used to find out exactly how the pattern of the line would carry on. One of my graphs which tested the variable: concentration of solution, showed a pattern which looked like the line was going to curve but it's not that obvious, so by carrying on using more concentrations, the pattern should become clearer. If I had to do this experiment again I would use more concentrations to be sure which direction the line would continue in and then I would be able to come to a conclusion, which I would be confident about. My other graphs which tested the following variables: distance between electrodes and depth of solution, both looked like the line would carry on straight although I would still like to use a wider range of values to be more accurate.
I am confident about my conclusions for two of the variables testing: distance between the electrodes and depth of solution because the pattern on the graph looks like it will continue in a straight line. However I am still not confident about my conclusion for the variable testing: concentration of solution, because it is difficult to work out whether the graph will curve or soon level off. Therefore I will need a wider range of values.
If I could do further work on this experiment I would improve the method of it by using equipment which can hold the electrodes secure for the duration of the reading. Therefore I will receive very accurate results when I repeat them. I do think though that 3 repeats is enough to get an accurate average reading so I would not increase the amount of repeat test if I was to do this experiment with more precise work. Controlling the outside condition is very difficult because I can't control the temperature of room temperature, but to make it a fair test, I would carry out the three experiments in the same room so the temperature would be roughly the same. As I have mentioned before, I will make the range of values wider to see what direction the line of best fit will continue in especially for the variable testing: concentration of solution.
Overall though, I think my performance of the practical experiment was very organised and accurate which is reflected in the results I obtained.
