The effects of electrolysis of Copper Sulphate Solution and copper electrodes
Rory Franklin Chemistry Coursework 03/07/2001
10ABC Planning
Aim:
We are investigating the effects of electrolysis of Copper Sulphate Solution and copper electrodes, and the effects of changing the voltage of the current flowing through the circuit. We are keeping the concentration and the temperature constant.
Background Information:
I know from my own knowledge that electrolysis is the breakdown of a substance by electricity. I also know that opposite charges attract, this means that positive ions are attracted to the Cathode (-ve) and negative ions are attracted to the Anode (+ve). I know from the preliminary experiment that we did, that the Anode LOSES mass, whilst the Cathode GAINS mass. This is because the positive ions from the Anode are attracted to the Cathode through the Copper Sulphate solution and this means that the Cathode gains weight and the Anode loses weight.
The equation at the Cathode is: Cu²+ + 2e¯ Cu
The equation at the Anode is : Cu - 2e¯ Cu²+
Faraday's Law: Michael Faraday did lots of the early work on electrolysis, and we know because of his work that it takes 96500 coulombs to deposit one mole of a metal with a single charge. This is called Faraday's Law. So, because copper has a charge of 1+, we know that it takes a charge of 96500 coulombs to deposit just 1 mole of copper. The equation fro the charge is:
Charge = Current X Time
(In Coulombs) (In Amps) (In Seconds)
PREDICTION:
I predict that the Anode will lose mass and the Cathode will gain mass. I also think that the amount of weight lost at the Anode, will equal the amount of weight gained at the Cathode. I predict that as the voltage increases, the weight loss/gain will increase. I know this from my own knowledge that opposite charges attract and the copper atoms from the Anode lose 2 electrons and enter the solution as Cu²+ ions. Because these are +ve ions, they will ...
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Charge = Current X Time
(In Coulombs) (In Amps) (In Seconds)
PREDICTION:
I predict that the Anode will lose mass and the Cathode will gain mass. I also think that the amount of weight lost at the Anode, will equal the amount of weight gained at the Cathode. I predict that as the voltage increases, the weight loss/gain will increase. I know this from my own knowledge that opposite charges attract and the copper atoms from the Anode lose 2 electrons and enter the solution as Cu²+ ions. Because these are +ve ions, they will be attracted to the Cathode because opposite charges attract.
Equipment:
For this experiment we need the following equipment:
* Safety goggles
* A beaker of Copper Sulphate solution,
* Two copper electrodes,
* A power pack with a variable voltage dial,
* A voltmeter,
* Three sets of wires,
* Crocodile clips,
* A beaker of distilled water,
* A beaker of Propanone,
* A stop clock,
* A set of electric scales.
Safety:
To make sure that we do not get any harmful substances in our eyes, we always wore safety goggles.
Method:
We weighed the Anode and the Cathode and wrote down the weight in the Results Table. We connected a wire from the power pack to the voltmeter and had another wire connecting from the voltmeter to the Anode, then, we connected a wire from the power pack to the Cathode. Then we put the two electrodes into the Copper Sulphate solution making sure that we did not touch the two together. This would make the experiment fail because the current would pass directly through the two electrodes meaning that electrolysis would not occur and therefore the results would be wrong making the experiment void. When we were sure that the circuit was correct, we turned the power pack on and set the voltage to 2 Volts, we then left the experiment for ten minutes. After the ten minutes is up, we washed the electrodes in distilled water and then in Propanone, Propanone acts as a drying agent because it dries much faster than normal liquids meaning that the time taken for the experiment is reduced. After the electrodes are dry, we measured them and wrote down the results in the Results Table. We ten repeated the experiment using voltages of 3V, 4V, 6V, 8V and 10V's. We repeated all the experiments to make sure that there were no anomalous results. Also, if we got any of the Copper Sulphate solution, or, the Propanone on our hands, we washed them as soon as possible because Copper Sulphate solution is poisonous and so is the Propanone.
Diagram:
Results:
Volts
Before expt:
Anode
Before expt:
Cathode
After expt:
Anode
After expt:
Cathode
Weight change (g)
Anode
Cathode
2
.28g
.34g
.28g
.34g
-0
+0.00
3
.28g
.34g
.27g
.35g
-0.01
+0.01
4
.27g
.35g
.26g
.35g
-0.01
+0
6
.26g
.35g
.25g
.36g
-0.01
+0.01
8
.25g
.36g
.23g
.37g
-0.02
+0.01
10
.23g
.37g
.20g
.40g
-0.03
+0.03
12
.21g
.39g
.18g
.41g
-0.03
+0.02
We repeated the anomalous results to try to get a better set of results; here is the results, and what we got for the repeated results:
Volts
Before expt:
Anode
Before expt:
Cathode
After expt:
Anode
After expt:
Cathode
Weight change (g)
Anode
Cathode
2
.28g
.34g
.28g
.34g
-0
+0.00
3
.28g
.34g
.27g
.35g
-0.01
+0.01
4
.13g
.46g
.12g
.47g
-0.01
+0.01
6
.26g
.35g
.25g
.36g
-0.01
+0.01
8
.15g
.44g
.13g
.46g
-0.02
+0.02
10
.23g
.37g
.21g
.39g
-0.02
+0.02
12
.18g
.41g
.15g
.44g
-0.03
+0.03
Red = repeated results
Analysis:
We found from this experiment that as you increase the voltage running through the circuit, the mass gain/loss increases. However, as the voltage gets higher, the increase/decrease gets bigger. E.g. at 2 volts, the increase/decrease was +0.00g, at 6 volts it was +0.01g and at 12 volts it was +0.03. This proves my prediction right. The Anode lost mass, and the Cathode gained mass, the mass gain/loss was equal and as the voltage increased, the mass gain/loss also increased.
The graph shows that the increase of mass gain/loss started slowly and then built up towards the higher voltages. The graph also shows that the original mass loss/gain was completely wrong because there should have been a direct correlation between them, but there wasn't. The repeated results however, showed a direct correlation between the mass loss at the Anode, and the mass gain at the Cathode.
Evaluation:
The results were fairly accurate, but they could have been improved with more accurate scales because the scales only go to 2 decimal places. There were a few anomalous results, but the anomalous results in the first set of readings were probably due to human error, they could have been cause by the connections to the copper electrodes, or the power pack could have been faulty. The results that we got from this experiment were quite good, but we could have done with some more readings at higher voltages to really show the effect of voltage on electrolysis. There was a pattern in the results because they increased as the voltage increased, but the pattern would have carried on going if the voltage was even higher, but because of the equipment, and the cost of trying to use much higher voltages, we could not experiment into this. The results could support my conclusion because they DO increase as the voltage increases and that is what my prediction and conclusion both detail.
