The experiment carried out aimed to monitor the quantity of Copper (Cu) metal deposited during the electrolysis of Copper Sulphate solution (CuSo4) using Copper electrodes, when certain variables were changed. It was considered that the following factors could affect the deposition of Copper metal on the cathode.The time was chosen because it is an easy quantity to measure and record, whilst at the same time maintaining the other variables at a constant level. The other factors could be observed in later experiments, should time allow.
It is possible to predict that the relationship will be directly proportional between the time the current flows and the mass of Copper deposited on the Cathode (negative electrode). I can therefore predict that if I double the time of the experiment, I will therefore be doubling the charge. This statement can be supported by both of Faradays Laws. Faradays First Law of electrolysis states that: The mass of any element deposited during electrolysis is directly proportional to the number of coulombs of electricity passed Faradays Second Law of electrolysis states that: The mass of an element deposited by one Faraday of electricity is equal to the atomic mass in grams of the element divided by the number of electrons required to discharge one ion of the element. Another piece of scientific theory we can use to support our predictions is: At the anode (+): Cu ® Cu2+ + 2e- At the cathode (-): Cu2+ + 2e- ® Cu The copper at the anode releases copper ions and electrons, which float in the solution towards the cathode, where the copper ions and electrons deposit copper onto the cathode. It was necessary to have a rough idea of how the results would turn out.
This is possible to work out by using a series of simple of equations: Ø Charge (C) = Current (A) x Time (sec.) Ø Moles of Electrons or Faradays = Charge (C) / 96500 Ø Moles of Copper = Moles of electrons or Faradays / ratio=2 Ø Mass = moles x RAM If the Current is 0.2A and the time taken 5 minutes Ø Charge = 0.2 x (5×60) Ø Faradays = 60/96500 Ø Moles of Copper = 0.0006217/2 Ø Mass = 0.0003108 x 64 Ø Mass = 0.0199 grams If the Current is 0.2A and the time taken 10 minutes Ø Charge = 0.2 x (10 x 60) Ø Faradays = 120/96500 Ø Moles Copper = 0.0012435/2 Ø Mass = 0.0006217 x 64 Ø Mass = 0.0398 grams If the current is 0.2A and the time taken 15 minutes Ø Charge = 0.2 x (15 x 60) Ø Faradays = 180/96500 Ø Moles Copper = 0.0018652/2 Ø Mass = 0.0009326 x 64 Ø Mass = 0.0597 grams If the current is 0.2A and the time taken 20 minutes Ø Charge = 0.2 x (20 x 60) Ø Faradays = 240/96500 Ø Moles Copper = 0.002487/2 Ø Mass = 0.0012435 x 64 Ø Mass = 0.0759 grams If the current is 0.2A and the time taken 25 minutes Ø Charge = 0.2 x (25 x 60) Ø Faradays = 300/96500 Ø Moles Copper = 0.0031088/2 Ø Mass = 0.0015544 x 64 Ø Mass = 0.0995 grams These equations will help to support my predictions, as from these equations a theoretical table of values can be produced and those can be plotted against the actual results obtained. From this comparison, it will be possible to spot any anomalies in the results and from this explain why these may have occurred (see EVALUATION). METHOD The apparatus was set up as in the diagram below: Copper Sulphate solution (50cm3) was poured into a small beaker. The two copper electrodes were thoroughly cleaned using water and steel wool, to scratch off the layers of copper from previous experiments. The electrodes were weighed, their masses recorded and placed into the beaker containing Copper Sulphate solution. The electrodes were connected to a cell and ammeter.
A steady current flowed (0.2 Amps) and the experiment was stopped at definite times (i.e. 5,10,15,20,25 minutes). At these times the current was switched off and both electrodes were removed from the solution. They were then washed by dipping in distilled water, and dried by dipping into propanone (a highly volatile liquid which readily evaporates) and placed near an electric heater. Once clean and dry both electrodes were both carefully weighed and their subsequent masses recorded. RESULTS ANODE (+) TIME (MINUTES) ORIGINAL MASS OF ANODE (grams) FINAL MASS OF ANODE (grams) CHANGE IN MASS AT ANODE (grams) 5 12.491g 12.468g -0.023g 10 11.834g 11.792g -0.042g 15 12.528g 12.459g -0.069g 20 12.444g 12.365g -0.080g 25 11.098g 11.002g -0.096g CATHODE (-) TIME (MINUTES) ORIGINAL MASS OF CATHODE (grams) FINAL MASS OF CATHODE (grams) CHANGE IN MASS AT CATHODE (grams) 5 11.824g 11.848g +0.024g 10 12.456g 12.485g +0.039g 15 12.942g 13.011g +0.069g 20 12.967g 13.050g +0.082g 25 13.872g 13.983g +0.111g AVERAGE TIME (MINUTES) AVERAGE CHANGE IN MASS (grams) 5 0.0235g 10 0.0405g 15 0.0690g 20 0.0810g 25 0.104g THEORETICAL RESULTS TIME (MINUTES) THEORETICAL CHANGE IN MASS (grams) 5 0.0199g 10 0.0398g 15 0.0597g 20 0.0796g 25 0.0995g CONCLUSION The results obtained support the prediction that the longer the current is left to flow, the more Copper metal is deposited on the cathode. It is now true to say that if the time is doubled the charge is doubled, and therefore the amount of copper produced. Proof of this can be seen in the obtained results: In 10 minutes 0.0405 grams of Copper is produced.
In 20 minutes 0.0810 grams of Copper is produced. 0.0810 grams is exactly double 0.0405 grams.This proves the prediction that the longer the experiment lasts, the higher the charge and therefore, the higher the amount of Copper produced. The actual results produce an almost straight-line graph, showing that: Mass of Copper a Time current Flows Therefore, it has now been proved, through this experiment, that both of Faradays Laws Of Electrolysis are correct. Faradays First Law of electrolysis states that: The mass of any element deposited during electrolysis is directly proportional to the number of coulombs of electricity passed
Faradays Second Law of electrolysis states that: The mass of an element deposited by one Faraday of electricity is equal to the atomic mass in grams of the element divided by the number of electrons required to discharge one ion of the element. It has also been discovered that the copper anode releases copper ions and electrons, which form copper at the cathode. At the anode (+): Cu® Cu2+® 2e- At the Cathode (-): Cu2++ 2e-® Cu EVALUATION
Although this was a successful experiment, there were some factors of the experiment, which could have been improved to make it even more successful. One of these factors could have been the electrodes, which, even after a good clean were still quite dirty and obviously still had irremovable substances from previous experiments still attached to them. If this experiment were to be repeated for a second time, in need of greater accuracy, it would be imperative to have a new pair of electrodes, which have never been used before.
Another factor which may have affected the overall outcome of the investigation, may have been the fact that the practical work of the investigation was carried over from lesson to lesson, meaning that variables such as the concentration or the amount of the Copper Sulphate solution could have changed between lessons. To overcome this problem, a stock solution of Copper Sulphate should have been made so as the concentration remained the same at all times. The same electrodes and equipment should have been used throughout. Also, when weighing, the same electrical balance should have been used as there may have been slight differences between the two balances. This is what could explain the anomaly (freak result) in the graph.
I found this investigation very interesting and am looking forward to investigating more of the variables in this experiment, which may or may not affect the mass of copper deposited onto the cathode, such as changing the Current or Temperature variable.