more reactions may occur at the same time.
5). Concentration of the electrolyte- When the copper electrodes are placed
into a concentrated solution, there are
more ions that can be discharged in the
reaction. Therefore, in a higher
concentrated solution, there is more
electroplating.
6). Temperature- Temperature can give more energy to the copper to move.
When the temperature is higher, there is more energy
available for the copper ions to move from the anode to the
cathode. When the temperature is low, there is less energy
available for the copper ions to move from the anode to the
cathode.
Prediction
I predict that the outcome to be is that as the amount of input increases, the amount of copper being gained increases. I predict that, initially a higher current will result in more copper being transferred onto the cathode, but with a much poorer standard of adhesion. And that repeats carried out at lower currents will be characterised by small amounts if better adhered metal being transferred. The optimum conditions will be a compromise between these two, a layer of metal plate applied as rapidly as possible yet maintaining a high degree of adhesion.
Preliminary Investigation
I have decided that, since it would be easy to control metal ion concentration, electrolyte PH, and the nature and amount of all substances present in the electrolyte simply by mixing one large reserve of electrolyte, it would be wrong to alter one of these factors. Another factor affecting electroplating, is the amount of cathode and anode that is submerged in the electrolyte, in my opinion it would be easiest to overcome this possible inaccuracy by ensuring that during all repeats both are completely submerged.
Current and time are both easily varied, and from precious work I know that current makes a great difference to the way in which the metal is deposited on the cathode whereas time tends more to effect quantity of material transferred. Therefore I have decided that the optimum conditions are most likely to be found through a variation of current. I will do this whilst keeping all of the other factors as uniform as possible. I will also carry out a series of pilot test, using the same method as described for the main procedure to find a suitable range in which to conduct my repeats. The volume of the concentration of the electrolyte was decided by doing some small tests in advance and observing which volume is best for electroplating. I found out that 40cm3 is the correct volume to use for my experiment. I also carried a few tests to decide the lengths; it was decided by whether the certain various lengths are best for electroplating. And by my results I found that 5cm was the best length to use.
APPARATUS
- Glass beaker
- 1-24V Power Source
- Variable resistor
- Cable wires
- Top pan balance (accurate to 2dp)
- Ammeter
- Stopwatch
- Copper II Sulphate solution
- Carbon electrodes
METHOD
- Connect two terminals of circuit.
- Attach carbon anode to positive terminal of circuit.
- Attach carbon cathode to the negative terminal of circuit.
- Pour 40ml of copper II sulphate into the beaker.
- Lower cathode and anode into the beaker containing copper II sulphate.
- Record masses.
- These steps are repeated two more times.
- Next averages are found.
- These should be put into a table.
PRELIMINARY ANALYSIS
From my previous found out, stated out in a table it shows what figures should be used for the real experiment
The experiment was timed for a fixed time interval of five minutes. The range of current:
- 0.2A
- 0.3A
- 0.4A
- 0.5A
- 0.6A
- 0.7A
- 1.0A
Once the carbon electrodes had been measured and placed in equal distance in the beaker, and the copper II sulphate solution was there, the power source was turned on. 0.2A was kept constant for five minutes so the current does not fluctuate by the variable resistor. After the five minutes the electrodes were removed from the solution. Making sure that the reading for the mass is accurate.
OUTLINE PLAN
Fair Testing
The electrodes should not be blown on or wiped, instead they should be shaken. So this does not interfere with the readings and results. The surrounding temperature has to be roughly constant through out the experiment in order to make it a fair test. Also the solution have to be the same amount, in this case I will be repeating 0.2A, 1.0A and 0.6A twice because they are in order of low, medium and high range of my experiment and also I could take the average results of them. After each experiment the electrodes are put into ethanol again to clean the excess copper sulphate solution, which might affect the change in mass in them.
ACTUAL EXPERIMENT
RANGE OF MEASUREMENTS
My investigation is to see how the different currents affect the amount of mass of copper deposited. Therefore current has to be varied in every test. I am going to investigate the current at 0.2A, 0.3A, 0.4A, 0.5A, 0.6A, 0.7A and 1.0A. It is possible to get easily in the lab, and it can indicate by a normal ammeter as well; it can reduce the effect of temperature rise in the reaction. The advantage is that the results will be reasonable results because they are not too high or not too low. The experiment will be left for five minutes as I think it is a reasonable tome for the experiment.
Apparatus
- Glass beaker
- 1-24V Power source
- Variable resistor
- Cable wires
- Top pan balance (accurate to 2dp)
- Ammeter
- Stopwatch
- Copper II Sulphate solution
- Copper electrodes
Detailed Method
- First connect the two terminals of the circuit.
- Using the ammeter to measure the current flowing through the circuit.
- Then use the variable resistor to adjust the resistance of the circuit to the required current.
- Next attach a copper anode to the positive terminal of the circuit.
- Then weigh a copper cathode and record its mass.
- Then weigh a copper anode and record its mass.
- Then attach the copper cathode to the negative terminal of the circuit.
- Then pour 40ml of copper II sulphate into a beaker.
- Then lower the cathode and anode into a bath of copper II sulphate solution, ensuring that both are fully submerged.
- Then leave the circuit complete for five minutes.
- Then put two drops of alcohol on the electrodes after removing after five minutes.
- Then allow drying by shaking them.
- Then weigh the cathode and subtract the mass from the new mass, then its area divided it.
- Thus is the amount of copper transferred per unit area.
- Next weigh the anode and subtract the new mass from its starting mass.
- Then is divided by the area of the copper electrode.
- This is the amount of copper transferred per unit area.
- Then the process is repeated with the same current flow twice, or until three concordant sets of results are available.
- Then the results recording should continue while altering the current.
- Next present the results for every repeat in table form.
- Lastly, find the averages.
Safety
Copper Sulphate can be toxic and should not be swallowed. Although the variable resistor will eliminate the danger of shorting, care should still be taken when working with electricity and liquids, avoid contact between the two elements. Ineffective electroplating can produce a finely divided solid of copper, avoid contact between this and the eyes, and also avoid digesting it. Hands should be washed thoroughly after each experiment. The usage of safety glasses is necessary in case of violent reactions occurring and electrical devices are in operation. The usage of aprons is required as chemicals may be spoil or stain the clothes of the chemists. Gloves should be also used due to the usage of chemicals so they do not cause damage to the skin.
The ammeter is also a safety precaution to ensure that the current was not too high, and the current should be controlled and kept at constant level of decrease or increase. Electric equipment should be handled with dry hands so that electrocution does not occur. It is essential to set up the circuit properly, especially to set up the ammeter; we have to make sure that the positive of the ammeter connects to the positive of the circuit. And the negative of the ammeter connect to the negative of the circuit.
ANALYSIS
From the experiment and by looking at the graph I have presented, it can be worked put that the amount of change in mass is directly proportional to the change in current. It is meaning that the amount of mass lost and gained during the experiment of electrolysis depended on the amount of charge that is put in so the more you put in the greater the amount of mass lost and gain.
From the graph when the best-fit line is drawn I can see that they do line up but for the cathode graph it is not as perfect though. This is because of some errors had occurred during the experiment. Comparing to the actual amount of mass lost I am not very far off. The method and the equation I have mentioned early on in background knowledge can calculate the actual mass change.
The prediction I have predicted has come out to be exactly the same as the experiments, which is that the change in mass will be proportional to the change in current. The graph of the results of the experiment when compare with the one of the actual mass it looks quite the same but some are anomalous, the anomalous results were circled in the graph to distinguish from the other values.
CONCLUSION
Due to my results, it shows that during the process the anode loses mass because the copper atoms lose electrons and become copper ions, Cu2+ (aq).
Copper atoms → copper ions + electrons
Cu(s) Cu2+ (aq) 2e-
The electrons released at the anode travel around the external circuit to the cathode. There the electrons are passed on to the copper ions, Cu2+ (aq), from the copper II sulphate solution and the copper is deposited or copper plates on to the cathode.
Copper ions + electrons → copper atoms
Cu2+ (aq) + 2e- → Cu(s)
According to my results it showed that when the current increases, the mass gained on the cathode also increased. They are directly proportional to each other. The mass gained is directly proportional
to the current in the circuit. It is because when the current is 1A, there is one unit of electrons that have been discharged, and become copper cation. These ions have been attracted by the cathode, at the same time, the gained electrons from the cathode, and become copper atoms again and deposited on the cathodes.
Cu2+ (aq) + 2e- → Cu(s)
1 mole 2 moles 1 mole
We require 2 moles of electrons to produce 1 mole of copper atoms from 1 mole of copper cations. Also an increase in current means that there is more resistance which occurs in the solution. This gives out heat, which is an exothermic reaction. This meaning that there will be more collisions and more ions with enough activation energy to carry out a successful collision. Therefore the rate is increased.
EVALUATION
I am very pleased about the results that I have obtained. They are accurate, and they can enable me to prove that the theories in my predictions are correct. There are several points that I think I have done quite well to obtain these results. The method, which was used,
was reasonably good and the correct apparatus was used well also. It was very simple to set up and carry out, using the method which was chosen. It was simple and safe procedure. But there was room for improvement.
Using the purest copper available could also make the results more accurate. By using a digital ammeter to secure a much more accurate reading on the current flow. Using the digital rheostat, to keep the current the same, the sliding rheostat is much harder to use as moving it to try and establish a constant current flow was very hard. Using the current rheostat, the current readings were fluctuating and were complex to maintain its stability. The copper II sulphate solution should be kept constant and stable.
I would use all the apparatus to its full potential. This would make my results even more accurate. All my results fitted the pattern. I would carry out another experiment but this time change the concentration of copper II sulphate solution every time the experiment was carried out, but in different concentrations. I would keep all the other variables the same and see if the change in concentration affected the mass gained on the cathode.
The experiment went quite well as I expected, except some occasional errors that have occurred during the experiment. The errors that occurred causing some of the result to be odd could have been that:
- The electrodes I used were not the same for some of the experiments. Since the practicals were done on different days.
- The starting time was sometimes delayed, which might have caused the mass to increase.
- The surrounding temperature was not the same through out the experiment but theoretically the surrounding temperature does not have the affect on the decomposition of the solution.
- The amount of current might have caused the decomposition to be different because if the amount of current was increased due to the conductivity of the solution. This will cause the decomposition to slow down.
- The results that I have corrected I think that they are accurate enough to the actual results to be obtained.
- It is accurate enough because for some of the experiments I did them twice to get the average result. This method is the best way to make the result accurate as possible.
- The experiments could have been improved by that the rheostat could have been change to an electric one, which is more accurate and it would have given better results.
