Apparatus:
- Power pack for supply electricity.
- Ammeter for measuring current.
- Variable resister to control flow of current keep constant at 0.2A.
- Beaker to contain Copper Sulphate solution (Cu SO4.
- Copper electrodes marked A for positive (+ve) electrode and C for negative (-ve) electrode.
- Top pan balance for taking mass.
- Measuring cylinder for measuring 50cm3 of Cu SO4.
- Leads and crocodile clips for making up the circuits.
- Stop Clock for measuring length of time.
- Heat proof mat.
- Goggles for safety
- Tweezers for holding.
- Copper electrodes.
- Paper towels to clean electrodes before weighing.
- Some form of exercise book or note book to take down results or indifferent reactions.
List Of Variables:
1)Time – How long current flows.
2)Current.
3)Concentration of solution.
4)Size / shape of electrodes.
5)Distance between electrodes.
6)Surface of electrodes.
Intention:
My intention is to investigate and measure how time affects the amount of copper deposited.
Fair Testing:
I plan to ensure fair testing by changing only the time and keeping all the other variables the same throughout.
Prediction:
I predict that as you double the current the amount of copper deposited is also doubled.
Predicted Amount Of Copper Deposited At Cathode:
For 5 minutes charge = Current (A) x Time(s) = 0.2A x ( 5 x 60 ) = 60C.
96,500C = 1 mole of electrons.
1C = 1 moles of electrons.
96,500
60C = 1 . x 60 = 0.00062 moles.
96,500
1 mole of copper electrons give 32g of copper.
0.00062 moles gives 32 x 0.00062 = 0.0199g.
Predicted amounts of copper deposited at cathode:
For 10 minutes = Charge (A) x Time(s) = 0.2A x (10 x 60 ) = 120C.
120C = 1 . x 120 = 0.00124.
96,500
0.00124 moles gives 32 x 0.00124 = 0.03968g.
Predicted amounts of copper deposited at cathode:
For 15 minutes = Charge (A) x Time(s) = 0.2A x (15 x 60 ) = 180C.
180C = 1 . x 180 = 0.00186.
96,500
0.00186 moles gives 32 x 0.00186 = 0.05952g
Predicted amounts of copper deposited at cathode:
For 20 minutes = Charge (A) x Time(s) = 0.2A x (20 x 60 ) = 240C.
240C = 1 . x 240 = 0.00248.
96,500
0.00248 moles gives 32 x 0.00248 = 0.07936g
Predicted amounts of copper deposited at cathode:
For 25 minutes = Charge (A) x Time(s) = 0.2A x (25 x 60 ) = 300C.
300C = 1 . x 300 = 0.00310.
96,500
0.00310 moles gives 32 x 0.00310 = 0.09920g.
Method and Safety:
I will set up a circuit as seen in my diagram of apparatus. This circuit will test faradays law by checking how much copper is deposited at the cathode. To ensure safety, I will wear goggles and also use tweezers for picking things up, also a heat proof mat to avoid spillage on working area. The variable resistor will ensure that current is kept at 0.2A . The experiment will be carried out over several lessons to avoid rushing.
Results:
Anode (+)
Cathode (-)
Average
Theoretical change in mass:
Proving with graphs:
My line of best fit to show where it more and less averages out to.
Conclusion:
My results did not support the predicted results, I predicted that as you double the current the amount of copper deposited is also doubled. If you leave the current on longer, then more copper is deposited and my results do not show that. Theoretically the test results should have showed a pattern of increasing change of mass after each increasing period of time but it never. According to Faradays law as the time the current is left on for doubles then the change in mass of electrodes should double also. I observed no change in the mass for five minutes so I need to repeat this measurement. There is no obvious pattern in my results although there is more change in mass for 20 and 25 minutes then for 15 minutes. Overall, as the copper ions dissolve into the solution at the anode and deposit on to the cathode during electrolysis. I should have observed that doubling the time doubles the change in mass of electrodes.
Evaluation:
My results did not support the predicted results, altogether and there are several odd results. I predicted that as you double the current the amount of copper deposited is also doubled. If you leave the current on longer, then more copper is deposited and my results do not show that. Theoretically the test results should have showed a pattern of increasing change of mass after each increased period of time but it never.
There may be certain causes for this maybe because the experiment was done over several days. Also at certain points in the experiment there seemed to be copper particles floating on the surface of the copper sulphate solution. This means that the copper is not where it should be (on the cathode). Other causes of my bizarre results could be that we made a mistake with the measuring of mass of the cathode and anode. I used the tweezers but did not make everything dry so there was water on it., and depending on how long it takes to measure the mass the amount of water left on would affect the weight. It became impossible to adjust the resister to 2.0A after trying everything I could I got it to 2.2A.
So there were one or to mistakes that were only noticed after the experiment. That i would without doubt be aware of if i ever get the chance to retake the practical. My results did prove the Faraday theory wrong. In fact though I believe that if it were not for my mistakes the Faraday theory may easily be correct. I only had one set of results so the experiment needs to be repeated for more reliable results.
This was the first time I have ever done an experiment with electrolysis and found it fascinating and hope next time I carry out this practical I do it more fairly as I had planned it.
I could also investigate other factors besides time such as copper sulphate concentration, distance between electrodes, changing the current. Being methodical and precise about the way the electrodes were hung into the solution in the beaker is very important so I would take care with that.