0.6 Amps
- 1200 = 720 Q
So: (59/193000) 720 Q
= 0.220g of nickel in theory should be lost on the anode and gained at the cathode.
0.8 Amps
0.8 1200 = 960 Q
So: (59/193000) 960 Q
=0.2934g of nickel in theory should be lost on the anode and gained at the cathode.
In theory this results show how much should be lost at the anode and gained at the cathode.
My graph has shown me that the theoretical values were different to my results. There are many areas of error during this experiment that could have affected the accuracy of the results.
When you look at my results you should notice that as the current increases the mass of nickel lost at the anode and gained at the cathode increase. I have constructed a graph to try and help you understand the results better, which is on the previous page. My prediction was that the mass of nickel lost at the anode would be equal to the mass of nickel gained at the cathode. This has slightly happened in my experiment, and there is a pattern in my results. This is that ‘as the current doubles the amount of nickel lost at the anode and the amount of nickel gained at the cathode doubles’, the results should make a directly proportional graph, but this is only to a certain extent. This happens because of the increase in current. The increase of current causes the ions to because they gain more energy and move faster causing them to deposit more nickel. Also as the current increases this might heat up the solution increasing the reaction time slightly.
This statement is more accurate when looking at the results of the ‘decrease in mass at anode’ column.
I can explain this. The decrease of mass at anode is closer to the above statement because it is nearer the theoretical value, which is as the current doubles the amount of nickel lost at the anode and the amount of nickel gained at the cathode doubles.’
Also when the nickel is lost at the anode not all of the nickel could have successfully transported from the anode to the cathode, some of could have be lost. The nickel could have been lost for a number of reasons, which I will explain in my evaluation.
When the current is flowing through the electrodes and the experiment is active two reactions are taking place. One reaction is at the anode:
Ni Ni2+ + e
The anode is the positive electrode; it attracts negative ions. When the negative ions reach the anode they usually give up their extra electrons to the anode and turn into neutral atoms.
The reaction taking place at the cathode is:
Ni2+ + 2e Ni
Electrolysis is the flow of electrons, which splits up a compound using electricity. The ions only start to move when current is present and when they become charged, this allows them to move when they become molten or a liquid. In our case the nickel sulphate solution. The cathode is negative; it attracts positive ions (nickel). When the nickel reaches the cathode they pick up electrons from the cathode and turn into neutral atoms. As you can see in the above equation this has happened. The nickel has a ‘plus 2’ charge and has been attracted to the cathode because its negative. The nickel has picked up two negative electrons to make the nickel neutral. I have drawn a diagram below to try and help to understand the reaction better:
The accuracy is very versatile due to the wide range of error that could occur. The amount of error occurs more when the current increases as you can see from my results.
The theoretical values have such a difference to my actual results because of the area of error, because some ions and atoms of nickel were lost. I.e. some of the nickel could have been deposited at the bottom of the solution this causing the masses to be different. Other errors such as slight increases and decreases in the current affected the deposit of nickel, but this could not be helped due the accuracy of the variable resistor. Other factors such as temperature change could also have effected the reaction rates. Also the distance and depth of the electrodes could have been changed, which would have effected the results.
Evaluation
After completing my experiment my results were not too accurate compared to the theoretical value. This could have been because of the huge area of possible error. All of my results followed a trend apart from one anomalous, which I have circled on my graph. Within this experiment there is a high area of inaccuracy compared to the theoretical values. The actual results did not actual follow the pattern but were not very close to the theoretical values, but the results did double roughly if the current doubled, which was a trend of the theoretical values.
I only had one anomalous result and this was probably due to human activities. The experiment could not have been timed properly or I wasn't watching the current to make sure it was the same. I had to watch the current because it was constantly changing current so every time it did I had to change the position of the variable resistor so the current would go back up or down to the correct current. Also when the current increased it could have heated up the solution ever so slightly, which would alter the reaction rate and therefore effect our results. Temperature change could of effected the results because an increase in temperature means that the ions and atoms increase in speed resulting in more numbers of reactive collisions therefore increasing the reaction time. The anomalous result was at 0.8 amps, which is the highest current I went up to, which shows that my explanation for the anomalous result could be true. Some other errors that could have occurred was that the electrodes could not have been at the same depth at every experiment. The electrodes could have not always been parallel. All these could have affected the results and made it an unfair test. Also before we put the nickel in we cleaned it with wire wool and dipped it in acetone to get any residues of it, which might have affected the results. If the acetone was still on the nickel when we placed it into the solution it could have diluted the solution of could have prevented the nickel ions attaching to the cathode. Also when we took the cathode out to measure its weight some of the solution could have still been on the cathode and therefore could have affected the results. The rate of reaction can be very versatile due to small increases in temperature, current and concentration of the solution.
I think that I did do enough results because I was able to take an average, which made my results more accurate. Also because I had taken three results I was able to afford an anomalous result and still able to take an average.
We met a number of problems while carrying out the experiment. These were things like keeping the current the same, the temperature the same, the electrodes at the same depth and to make sure they are always parallel. It was also difficult to make sure the cathode and anode were completely dry when we weighed them because the slightest moisture on them could have effected the weight, the scales were very accurate (2 DP). All these factors had to be kept the same because it could have effected the rate of the reaction or could have made our results less accurate. Another problem that I came across was that when I took out the cathode after the experiment the nickel attached to the cathode was not securely attached and some of it flaked off. This would effect our results because the weight of the cathode would be less than it should be if some of it flaked off.
If I were to repeat this experiment again I would improve the accuracy of my results by reducing the field of error. I would do this by using more accurate current equipment. I could also make sure the nickel cathode was completely dry before I weighed it. I could perhaps dry it with a hair dryer or just simply leave it for longer so the liquid has more time to evaporate. Another way to make my results more accurate is to make sure the electrodes are parallel by using a spirit level. I could also make sure the electrodes are at the same depth each time.
Other extra experiment I could do to support my conclusion more strongly is perhaps using a different metal like copper instead of nickel. I would have to keep all the input variables the same as what I did for nickel. I would have to find the theoretical value for copper and then do the same and then compare the two results and the two graphs to see if they are similar. If they are then it would back up my conclusion.
Another experiment would be to use a higher concentration of nickel sulphate solution. This would back up my conclusion if the results were similar. I would have to keep all the variables the same but change the concentration of the solution. I would again make a table of results and a graph and compare the two.