Reactivity Series:
Potassium
Sodium
Calcium
Magnesium
Aluminium
Plan:
Equipment:
- Electrolysis cell
- 12 volt power pack
- Sodium Chloride solutions (0.5 m, 1.0 m, 1.5 m, 2.0 m)
- Measuring cylinder
- Ammeter
- Electrical wires.
To carry out the experiment I will need the equipment above. Firstly I will have to keep a constant voltage through out the experiment such as 12 volts. Using a measuring cylinder I will pour out 100 cm3 of sodium chloride into an electrolysis cell. I shall need four electrolysis cells as there will be four different molar concentrations of sodium chloride which are mentioned above in the equipment section. Safety will also need to be considered as chlorine gas will be given of. I will also need to consider the amount of time I leave the electrode in the solution because if I leave them in the solution too long then chlorine gas could be inhaled and if I leave the electrodes in the solution too little then the results might not be accurate so a set time will be considered. For example I could leave the electrodes in the solution for ten seconds and then take them out. I will also make sure that the electrodes go fully into the solution by holding the base of the electrodes down firmly because if most of the electrode is in the solution then more electricity will flow through and if it is uneven then not all of the electricity will be flowing through the solution which will lead to differed results. When coming to take measurements I will be taking three measurements from each molar solution. I feel three measurements would be adequate enough to give me a good set of results.
Method:
To start the experiment I needed the equipment listed above. Firstly I poured the molar solution(s) into the electrolysis cells and then connected the power pack to the socket. To measure the amount of solution going into an electrolysis cell I used a 100cm3 measuring cylinder. This was to enable accuracy. I poured the solutions into four electrolysis cells as there were four different solutions. I then collected the ammeter, the electric wires and connected them to the right parts of the power pack and the electrodes. I then started the experiment. I started the experiment at 12 volts and noticed that when I got to a higher concentration such as 2.0 molar chlorine gas was given of rapidly. I also repeated the experiment three times i.e. that I took three measurements from a molar concentration three times in the 12 voltage region. I repeated the experiment for specific reasons. If you repat an experiment you get rid of previous errors and in this case perhaps the electrodes were not fully in. More the times you repeat an experiment more the accurate the result. I did the other experiment on two other voltages, they were 6 volts and 4 volts and the same was conducted on these two voltages as was done on 12 volts. I took three measurements of a molar concentration so I could get a good average. Safety was also considered. Within a group we set rules so we could keep safe. One of the main concerns was of electricity and chlorine gas. So we never handled anything with wet hands and for the chlorine gas concern we set a time for how long we should leave the electrodes in the solution. We said that the electrodes should be left in the solution for a maximum of ten seconds.
Results:
Tables to show the results of the current received when the electrode was put into increasing concentrations
Line graphs to show the relationship between the increasing concentration of sodium chloride against electric current
For 12 Volts:
For 6 Volts:
For 4 Volts:
Analysis:
Looking at my graphs we can see a general pattern. The general pattern for all the graphs is that as the concentration increases the current increases. The line of best fit which is the black line shown on all graphs is angled diagonally upwards i.e. that the current is proportional to the concentration. Looking at the graph for 6 volts we see that clearly happening. At 0.5 molar the current is approximately 0.45 amps and as the current increases, at 1.5 molar it is approximately 0.74 amps. This is also accounts for the graph at 12 volts. This means that my prediction is correct. I had predicted that as the molar solution of sodium chloride increased the current would increase. As the concentration increases there are more ions of sodium chloride in the solution so more electrolysis happens. To do this more current is needed to flow through the electrolyte to split up the compound of NaCl hence the current increases. This is because the current is the flow of electrons so more the ions in a solution more the current. I also know that my prediction is correct because when observing this experiment there were bubbles of chlorine gas coming of the anode. It couldn’t have been sodium because that is too reactive to attach to the cathode in the first place so it has to be chlorine gas coming of the anode which I could smell which concludes to my prediction being correct. Below is a diagram shows how the hydrogen and chlorine gases form at the respective electrode.
At the Anode:
All non metals except hydrogen have negative ions and so they will be produced at the anode. Negative ions are called anions because they are attracted to the anode. This proves my prediction right because at the anode chlorine gas will be given of as chlorine is negative proving the formula right: 2Cl- - 2e- → Cl2 (g)
At the Cathode:
Metals will always be produced at the cathode because metals form positive ions. Positive ions are called cations because they are attracted to the negative cathode. Looking at the diagram we can see that sodium should also be produce at the cathode but as we know sodium cannot be produced at the cathode because it is too reactive to form so hydrogen will be given of as gas again proving my formula: 2H+ + 2e- → H2 (g) and my prediction to be correct.
Evaluation:
Looking at my results I know they are reliable results. This is because my plan worked accurately. Even though, for the graph of 4 volts its line of best fit doesn’t go along with the average line of result is because there could have been something that I did wrong. However the lines on the other graphs have the general direction of going diagonally upwards or that current is proportional to the concentration. Yet still there could have been errors. The results could have been more reliable if I did each part of the experiment more than three times each. This would have enabled a better average. The more the times you repeat an experiment more the reliable the results which lead to a good average and it gets rid of anomalies.
I could have improved the experiment by putting the surface area of the electrodes fully into the electrolyte. This would have enabled a better circuit of the electricity in the electrolyte, and the required amount of electrolysis would occur. This would have lead to better results as well. I could have also used all the voltages to see the effect instead of three voltages which I used. Using all the voltages would give us a better understanding at what happens at each voltage. Another improvement could have been if I had more time to do the experiment. This would have lead to better measuring of the solutions because I could have made an error in measuring the amount solution of NaCl going into the electrolysis cell. For e.g. instead of measuring 100 cm3 I could have poured in an extra 3 cm3. This would mean that the solution with the extra 3 cm3 would have more ions than the other solution which would lead to differed results.
I know the results obtained were reliable because chlorine gas was given of the anode. Also the graphs show the general pattern of what was required. This means that electrolysis is a good method of separating a electrolyte such as NaCl.
If I were to redo the experiment I would use a wider range of sodium chloride i.e. not just 0.5, 1.0, 1.5 and 2.0 molar concentration which I used but 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, molar concentration but perhaps to an extent of 0.15, 0.2, 0.25 molar concentration to see what happens at these concentrations which will be used to show the general pattern even better. The other objective that I would do is use a different variable such as using different electrodes because you can get different material of electrodes. I used carbon rods. With this we could compare the electrodes and the overall results. I used a measuring cylinder but I could have used a burette to measure out accurately 100 cm3. Generally I feel the experiment was very good because two of the three graphs showed what I expected.
