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Size of Electrode – The larger the electrode, the more copper is merged into the cathode. This is takes place because there are more copper atoms, which can dissolve in the solution to form Copper Ions (Cu2+). The extra ions can then travel to the cathode and therefore raising the amount of copper ions entering into the cathode.
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Volume of solution – The greater the volume, the greater the amount of Cu2+ ions will be produced. This takes place because the larger the volume of solution, the greater the area of electrode is merged in the electrolyte, therefore the reaction will take place at a greater rate.
Applications of Electroplating
Electroplating has become a large and growing industry with sophisticated engineering and equipment requirements. Metals can be readily plated from aqueous solutions at high-current efficiencies. Metals are electroplated to stop the formation of corrosion, by several chemicals. Copper plating is used extensively to prevent case hardening of steel on specified parts. The entire article may be copper plated and the plate ground off on the areas to be hardened. Silver plating is used on tableware and electrical contacts; it has also been used on engine bearings.
Preliminary Experiment
The aim of the preliminary experiment is to see if some changes take place, and how they affect the experiment. The preliminary test concerned accurate measurements as there was no other way of finding out whether there was any changes taken place. I tested to find out the weight of each copper strip. The anode and cathode was weighed each time they had been electroplated to find out if they had gained weight or loss weight.
Anode
Cathode
Fair Testing
Fair testing is to make sure that all substances are used in the same amount. To do a fair test for this experiment you must have these substances listed below at the same amount:
- Temperature will always be at room temperature
- The volume of solution will always be at 50cm3
- The electrodes will always be at the edge
- Each experiment will last for five minutes
- A 6volt battery will always be used
Method
The following equipment was used to carry out the experiment:
- Conducting wire with clips
- Connect the positive terminal of the ammeter to the positive terminal of the battery using crocodile clips.
- Connect the negative terminal of the ammeter to an electrode.
- Connect the negative on the battery to the variable resister through one terminal (anode).
- Connect the other electrode to the free terminal on the variable resister (cathode).
- Once the anode and cathode are placed into the ionic solution the circuit was complete.
- Label the cathode and anode and find their mass using an electronic balance scale.
- Using a measuring cylinder, pour out 50cm3 of copper II sulphate solution
- To complete the setup and begin the experiment, place the electrodes into the copper II sulphate solution making sure they are parallel to each other.
- Clip them to the edge of the beaker and using the variable resister adjust the current to 0.2amps (starting amount),
- Start the timer
- Allow 5 minutes before disconnecting the circuit and removing the electrodes.
- Rinse the electrodes using acetone
- Weigh each electrode, and record the mass.
- Repeat steps 4-12 but varying the current each time at the following: 0.4A, 0.6A, 0.8A, & 1.0A.
Prediction
I predict that the out come is to be is the amount of input current will decrease & the amount of copper being gained will increase.
Results
Each experiment was timed for 5minutes.
Experiment 1
Experiment 2
Average set of results
Analysis
There are two straight lines of best fit through the origin, the red one is the mass gained at the cathode, and the black one is the mass lost at the anode. The lines are nearly as they should be, which is equal, as the mass lost at the anode should equal the mass gained at the cathode.
Cu(s) (r) Cu2 +(aq)+2e- (oxidation)
During the electrolysis of copper is the reverse of the cathode reaction:
Cu2 +(aq) + 2e- (r) Cu(s) (reduction)
So for every two electrons passing through the external circuit, one copper ion should be formed at the anode and one copper ion discharged at the cathode. One would expect the mass loss of the anode to equal the mass gain at the cathode. As explained earlier, for every two electrons, at the cathode one copper ion is discharged, whilst at the anode, one copper ion is formed This can be explained with the ionic theory, which basically states that the electrons flow away from the cathode, to the anode where the Cu2+ ions take 2 electrons from the negative electrode and become Cu atoms, thus mass loss at cathode = mass gain at the anode.
The amount of copper deposited on the cathode and lost from the anode depends on the number of electrons passing through the circuit, i.e. upon the charge passed through the cell. Now the charge passed, is related to the current. in amps and time, in seconds.
Evaluation
There were several sources of error in this experiment as none of the results were 100% accurate.
These errors could have been caused by the fact that not all the ions "stick" to the anode, and so end up at the bottom of the solution. This happens most at higher levels of current, and causes the mass lost at the cathode to be greater than the mass gained at the anode. Also the temperature of the solution rose at higher currents by 5 degrees Celsius. This would cause fewer ions to turn to copper at the anode, and make the current more, as there is less resistance. The size of the electrodes was also never exactly the same, as they were reused, so the amount of electrolysis differed from experiment to experiment. The separation of the electrodes was a small source of error, as they were not always exactly the same distance apart. The current which was controlled with the rheostat was not always the same, as the amount of copper decreases, so does the resistance, and so the current increases.
Other errors could have been caused by the apparatus, such as the ammeter, which is quite old, and may not be perfectly calibrated, and the scales, which only show the mass to 2 decimal places. The rest are cut of with out rounding. Therefore this experiment could have been made more accurate by using lower current values, with the same size and separation of electrodes, controlling the current so that the temperature is constant, and the current more accurately controlled, and using a more accurate ammeter and a balance which rounds the other decimal places.
My results showed many inaccuracies. At the 0.2A reading, the anode difference is 0.1A, and the cathode difference is 0.2A, both very small variations. For the 0.40A reading, the anode difference is 0.3A, a much smaller difference, and the cathode variation was greater, at 0.4A. The 0.6A anode difference was only 0.5A, and the cathode was larger at 0.6A. The 0.8A anode variation was 0.6A and the cathode was 0.7A. The final reading, 1.00A anode difference was 0.9, and the cathode variation was 0.10A. This increasing variation is caused primarily by two things, firstly the temperature of the solution increases more at higher current values, so the ions travel faster, and so do not stay on to the anode as well, and secondly the increased current itself has the effect of making less ions sticking to the cathode. The anomalous result for in the 0.40A value for the anode was probably caused by one or both of the crocodile clips touching the solution, so less electrons flow through the copper, and so less are transferred to the cathode.
The ranges of my results were from 0.2A to 1.00A, with an average discrepancy of ______from the average reading.
If this experiment was to be done more accurately, I would have to use more accurate apparatus, such as a newer ammeter, a balance with more digits, a more accurate way of controlling the current, maybe with a computer, and likewise with the temperature. I also could have kept the size and separation of the electrodes the same. I also could have made sure that the crocodile clips were completely out of the electrolyte. Also I could have taken a much wider range of readings, from 0.01A to 10A at smaller intervals, and I could have timed for different times, and I could have investigated the other variables, such as the temperature of the electrolyte, the concentration of the electrolyte, the separation of the electrodes, and the size of the electrodes.