An investigation into the factors which affect the current
flowing during electrolysis
Electric current is the flow of electrons. Sodium chloride in solution is able to conduct electricity because when dissolved sodium ions and chloride ions are produced. The chloride ions that are negatively charged due to their extra electron are attracted to the anode where they give up that extra electron and bond with other molecules to form the chlorine gas, Cl2. The extra electron then flows through the circuit to the cathode. H+ ions in the solution are attracted to the negative charge of the cathode and there they gain the extra electrons that originally belonged to the Cl- ions. Hydrogen gas is then formed and the circuit is complete.
2e + 2H+ → H2 2Cl- - 2e → Cl2
Concentration of NaCl- The bigger the concentration the more ions will be in the solution. This will mean that more ions will get to the electrodes, which means more electrons will get into the wire. This will greater the current.
This is a preview of the whole essay
Temperature- the ions will go quicker to the electrodes as the water will vibrate quicker when hotter. This will increase the current.
Voltage- The current would be decreased because by ohm's law v=ir
Surface area of the electrodes- if the surface area on the electrode increases there will be more space for the ions to go to and therefore the current will increase.
Out of these 5 variables I am going to investigate how the change in concentration can affect the current flow. I have chosen this one because I think that it is the most reliable and I think it will give me the more accurate results. This factor can be monitored very closely.
As the concentration increase by definition the number of Chloride ions in the solution will increase which means the current will also increase. If there are more chloride ions then more chlorine atoms will form giving off more extra electrons. Therefore the speed at which the extra electron in the chloride ions are transferred to the H+ plus ions will increase therefore the greater the concentration, the greater the current. Current is measured by the rate of flow of electrons. The more electrons there are, the faster the rate of flow will be therefore a higher current.
And so I predict that as the concentration increase the current shown on the amp will also increase
Concentration of Nacl
Preliminary Method and Results
A circuit was set up.
A 200ml beaker was used and 100ml of water was added to it. The power
pack was turned up to 6 volts. The electrodes were 8cm long. The range of sodium
Chloride added was from 1g-6g.
The results obtained were as follows:
These results are very low. 200ml of water was then tried so that 12g of Sodium Chloride could be used.
The results were as follows:
These results are still lower; maybe if the electrodes are longer the ions would get to them easier and therefore get to the wires quicker through to the other electrode.
The electrodes were lengthened to 12.5cm, 200ml of water was used. The range of
Sodium Chloride added was from 4g-12g. A tall, thin beaker was used.
The results were a lot better:
I am going to use this experiment because it gives me the best range of measurements.
My Final Method
200ml of water
A glass rod
2 Long electrodes
2 Crocodile clips
200ml of water are to be added to a tall, thin beaker. The circuit will be set
up with to crocodile clips attached to the anode and cathode. Electrodes of
12.5cm will be placed in the beaker. In turn different amount of Sodium Chloride
will be added to the water to form Sodium Chloride Solution. The amount of
Sodium Chloride added will be a range from 1g-12g as for safety reasons only
6g/100ml of water is allowed. After the Sodium Chloride is added it will be
stirred with a glass rod until the solution is made. The voltage used will be 6v. The NaCl will be added one gram at a time.
To make sure this is a fair test I will control all my other variables.
- The length of the electrodes will stay at 12.5cm.
- The water level will stay at 200ml.
- The voltage will always stay at 6v.
For safety reason the power pack will not be used over 6 volts because the
amount of chlorine given off must be controlled. The maximum amount of Sodium
Chloride used will be 6g/100ml of water. This is the method I would like to use but because of the apparatus in the lab I could not use a big beaker. This meant I had to shorten the electrodes to 10cm. This will not make too much of a difference as the electrodes are still longer than what they were in my first experiment.
The electrodes were 10cm
200ml of water was used
The amount of NaCl used ranged from 1g→ 12g
The experiment was done twice:
Here's what a star student thought of this essay
Quality of writing
#3# The spelling and grammar are good. The scientific language used was relevant and well placed, the only thing that could be done to improve this area is that the terms used to be explained to show an even deeper understanding of the subject
Level of analysis
#2# The explanation used in the first section of this essay shows that the student has a good understanding of electrolysis an how electricity flows, because they can transfer it to their ideas and predictions. It is a higher level skill if you can make links between different topics to come up with a explanation behind your theory. The way in which each of the experiments were carried out to come up with the final design was good, but more explanation could had been give as to why it was bad that the results were too low, was it was because the error would be to high in them or was it because it was had to determine a pattern between them?
Response to question
#1# The student has obviously thought very hard about how this experiment was going to be carried out. The response is very explicit as to how the experiment was carried out and how the final designed was determined but there was very little on the evaluation and interpretation of the final results. When conducting an experiment the interpretation is possibly more important than the experiment its self.