Metal ions are positive and non-metal ions are negative. We know that opposite charges attract, there fore the metal ions would be attracted to the negative electrode – The cathode – and the metal ions would be attracted to the positive electrode - The anode. For this reason we call the metal ions “cations” (from ‘Cathode’) and the non-metal ions “anions” (from ‘Anode’).
We know that the amount of electricity in the circuit affects the rate of electrolysis, as Faraday says in his first law that the amount of electricity in the circuit is directly proportional to the rate of electrolysis.
In electrolysis, the amount of substance at each electrode is stated in a Faraday’s law, which states that the quantity if material transformed at each electrode is proportional to the quantity of electricity passed through the electrolyte.
I am going to do two experiments, varying two factors to find what effects the rate of electrolysis the most. For the experiments I will use Copper Sulphate solution as the electrolyte and copper electrodes.
Change in Current
Aim: To investigated how the rate of electrolysis is affected when changing the current in the circuit.
Hypothesis: Michael Faraday’s first law of electrolysis states:
“The mass of any element deposited during electrolysis is directly proportional to the number of coulombs of electricity passed”
This tells us that the amount of electricity we pass in this circuit will directly affect the rate of electrolysis.
When the circuit has electricity passing through it, the ions are floating towards the electrode. When the electricity is higher, the flow of ions is faster; therefore the ions will travel to the respective electrode faster, increasing the rate of electrolysis.
Prediction: Based on Faradays first law of electrolysis I predict that the rate of electrolysis will increase when more amps are passed through the circuit.
Apparatus:
- Copper sulphate solution (electrolyte)
- Copper Electrodes
- Small Beaker
- Power supply unit
- Variable resistor
- Crocodile clips and wires
- Ammeter
- Crocodile clips
- Stopwatch
Variables:
Dependant Variable: The mass of the electrodes
Independent Variable: The electricity put through the current, (amps).
Control: We did not change:
1) The temperature of the solution or electrodes (approx. 18°)
2) Concentration of the Copper Sulphate solution (1 mole)
3) Quantity of Copper Sulphate solution (50ml)
5) Time for each current (5 minutes)
6) Size of the electrodes
Method:
1) We put 50ml of Copper Sulphate solution into the beaker
2) We weighed the electrodes.
3) We set up a circuit using the power supply unit, the wires, variable r resistor and the ammeter. We made sure the ammeter was disp la displaying 1 amp.
4) We put the electrodes into the solution and we began to time.
5) After 5 minutes we weighed the electrodes again to see the change if in the weight and to see the rate of the electrolysis process at 4 damps.
6) We then repeated the experiment for 2, 3, 4, 5 and 6 amps.
7) we repeated the whole experiment to ensure accurate results.
Results:
Rate of decrease in the mass of Anode:
1st attempt:
Rate of increase in mass of Cathode:
1st attempt:
Graphs:
Analysis: The result table clearly shows us that when the current is increased, the rate of electrolysis is clearly increasing. This is shown by the faster increase of mass in the cathode and decrease of mass in the anode. The table below shows a clear pattern of how the mass change goes up in a pattern.
The graphs also show us how all our (normal) results go up in an almost straight line, indicating as Faraday’s law also states, that the charge is directly proportional to the rate of electrolysis.
Evaluation: The procedure we used to collect the information we have was quite effective but may have been improved by many factors. We could have repeated the experiments one more time, to absolutely ensure accurate results. Another factor which could have been improved is the fact that the power supply unit we were using was actually not working too well, which might explain the anomaly result we got.
The results we got from the experiment were what we expected, after referring to the laws of Faraday and from what we knew previously. There were some results that did not make sense, i.e in the 2nd attempt – The increase in mass of the cathode:
The increase in mass here is not proportional
to the current as it should be (Faraday’s
first law). The graph is not at all straight.
This may be because the power supply unit may
have been faulty, possibly between 3 to
4 amps. Another problem may have been our
Ammeter. It looks from the graph as if the
ammeter was not displaying the correct
information.
I think that apart from this strange result, my results are fairly accurate, and the conclusion we drew from them was proved to be correct by Faraday’s law. Based on this it can be said that our experiment, apart from a few strange results, gave us accurate results from which we may draw an accurate conclusion.
Other experiments that could be done in order to draw more conclusions on electrolysis include changing the concentration of the solution, changing the material used for the electrode, the size of the electrode and the temperature of the solution.
Electrolysis - By Time
Aim: To measure the rate of electrolysis at time intervals
Hypothesis: During electrolysis, the ions float towards the electrode of the opposite charge. Because we are not changing any factors that may affect the rate at which this occurs, the simple rule applies that with more time, there will be more time for the ions to float towards the respective electrode. Therefore the ions will flow at the same rate throughout the experiment but there will be more at the electrode with time.
Prediction: Based on the fact that we have not changed any factors affecting the rate of electrolysis, I predict the mass will change by the same amount each time.
Apparatus:
- Copper sulphate solution (electrolyte)
- Copper Electrodes
- Small Beaker
- Power supply unit
- Crocodile clips and wires
- Ammeter
- Crocodile clips
- Stopwatch
Variables:
Dependant Variable: The mass of the electrodes
Independent Variable: The time
Control: We did not change:
1) The temperature of the solution or electrodes (approx. 18°)
2) Concentration of the Copper Sulphate solution (1 mole)
3) Quantity of Copper Sulphate solution (50ml)
5) the current in the circuit (2 amps)
6) Size of the electrodes
Method:
1) We put 50ml of Copper Sulphate solution into the beaker
2) We weighed the electrodes.
3) We set up a circuit using the power supply unit, the wires, variable r resistor and the ammeter. We made sure the ammeter was displaying 1 amp.
4) We put the electrodes into the solution and we began to time.
5) Every 5 minutes we weighed the electrodes again to see the change in the weight..
6) We continued this up to 30 minutes.
7) We repeated the whole experiment to ensure accurate results.
Results:
Graphs:
Analysis: My prediction turns out to be correct. We can see from the tables and the graphs that the rate of electrolysis does not increase or decrease rather it continues steadily in a straight line. This is simply because the ions are constantly moving towards the electrodes, with no factors to increase or decrease the speed.
Evaluation: The procedure we used to collect the information we have was quite effective but may have been improved by many factors. We could have repeated the experiments one more time, to absolutely ensure accurate results. Another factor may have been the sale we used when weighing the electrodes. The scale was a very sensitive one, as this was what was required. We also used more than one scale, and any difference between the scales may have caused a strange result.
The result was got was what we were expecting, because of the factors that we did not change, and because the experiment was carried out in a suitable manner.
My results are fairly accurate, and this time I got not strange results or anomalies. I think we can draw an accurate conclusion from my results as they are quite accurate.
Other experiments that could be done in order to draw more conclusions on electrolysis include changing the concentration of the solution, changing the material used for the electrode, the size of the electrode and the temperature of the solution.