I am going to use time as my variable. I predict that as time increases there will be a greater decrease in the mass of the copper anode. I predict that this will happen because of preliminary work on electrolysis. This is because the copper changes into ions at the anode because it loses 2 electrons. This makes it positively charged so it moves over to the cathode, here it gains 2 electrons and turns back into metal but in pure form.
I will take samples every 2 minutes up to 20 minutes as I think that these will give me good enough results to draw up a conclusion.
To make sure that it is a fair test I will make sure that apart from time all of the other variables listed above remain the same.
Apparatus
Measuring cylinder
250 ml beaker beaker
75 ml of copper sulphate (concentration= 0.25 M)
Power pack
Electrodes (anode = copper, cathode = zinc)
Stopwatch
Scales
Wires
Crocodile clips
Propanone
Diagram
Method
1) I will weigh the copper anode and record its mass
2) I will then set up the apparatus as shown in diagram
3) I will turn the voltage on the power pack up to 9
4) After 2 minutes I will take out the anode and dip it in Propanone. This evaporates any of the copper sulphate on the copper so that it does not affect the mass. Then I will weigh the anode and record the results.
5) I will repeat these steps and weigh the anode after every 2 minutes up to 20 minutes and record the results.
Results
Conclusion
The results have told me that as time increases the mass of the copper anode decreases. There is a pattern that after every 2 minutes the copper anode decreases by 0.01 g. My graph shows this. The conclusion matches my prediction because I knew this would happen from preliminary work where we found out that the copper loses 2 electrons at the anode making it positively charged so it moves over to the cathode where 2 electrons are gained and turns back into metal but in a pure form.
Evaluation
I thought that our experiment worked as well as I expected and everything was according to the plan. The experiment helped me to prove my prediction because it showed that the anode decreased in mass. The only problem with our experiment was that the scales we used for the first weight were inaccurate which is why we got an anomaly but we used different scales after this to get more accurate results. I thought that we did take a sufficient amount of results us maybe a few more would have given us a clearer graph and a slightly better conclusion. Our range of results was good because we did from 0 minutes to 20 minutes taking a sample every 2 minutes. We could not have taken results from over 20 minutes because we did not have enough time. We did get an anomalous result; this was taken at 2 minutes. It was anomalous because the scales that we used to weigh the anode were inaccurate so I used different scales for the rest of the experiment.
If I were to do this experiment again I would have repeated the whole experiment with a different anode and cathode to see if the graph was the same and that the results were similar. This would have given me harder evidence to write my conclusion with.
Other factors I would like to have investigated were the concentration of the copper sulphate and also the volume of the copper sulphate.
