Effect of increasing charge on Mass of Copper Deposited
- I will fist weigh the cathode
- I will then set up the apparatus as shown in the diagram
- Then switch the power pack on
- I will wait 10 minutes and then weigh the cathode, I will do this for 50 minutes every 10 minutes
My Independent Variable is the Charge
My Dependent Variable is the Mass of the cathode
The controlled variables are the concentration of Copper sulphate and the temperature
I can predict that there will be a positive coloration between the increase of charge and the amount of copper produced at the cathode.
Current is the flow of electrons in a circuit - in the case of electrolysis the flow is towards the cathode and away from the anode. Within the solution, the current flows because of the presence of negative and positive ions. Copper sulphate is an ionic salt, which contains no free electrons. However, it does contain ions (which are charged particles) fixed in a crystalline structure. When copper sulphate is dissolved, the copper sulphate solution becomes an electrolyte because the ions become free to move and they can conduct electricity.
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At the cathode, the copper ions, being more reactive than the hydrogen ions are deposited whilst the hydrogen ions remain in solution. At the anode, the copper atoms from the copper anode give up their two electrons to make them stable. The electron flow in the electric current back to the power supply and the anode dissolves.
When the current is increased, more electrons are at the cathode attracting copper ions, which are positively charged and form a layer of copper atoms. At the anode, more copper dissolves into the solution releasing its electrons to flow back to the power supply. Releasing one mole of atoms of copper requires 96,500 coulombs of charge (1 faraday). One coulomb is the charge which flows when one ampere of current flows for one second. 1Charge= 6x 1018 electrons. Therefor 96,500 x 6x1018= 6x1023 electrons (Avagadro number) are the amount of electrons that arrive at the cathode.
Since each copper ion requires 2 electrons to become a copper atom, 1F of charge will deposit only half a mole of copper (32g). So 2F is required 2 deposit 1 mole of copper (64g).
- 2 copper electrodes - To collect the pure copper from the cathode and provide more copper in the solution.
- DC Power supply – To produce a current to pass through the solution
- Ammeter – to measure the current and make sure it is at the right value
- Beaker – contain solution and insulate it
- Wires – connect the electrodes to the power supply
- Stopwatch – to time the experiment
- Scales – to weigh the cathode
- Propanone – to wash the cathode and remove excess solution
I am going to measure, by weighing the copper cathode before and after each change in charge. I will weigh the cathode to the nearest 100th of a gram to give me accurate results on which to base my conclusion. I would expect the weight of the cathode to increase with increased current. The change in mass of copper indicates reaction rate so that the more copper deposited at the cathode, the faster the reaction rate. I will need to ensure that the cathode is washed with propanone, dried and re-weighed after each test to ensure a fair test.
In order to carry out a fair test, the only variable to be changed will be the current passing through the copper sulphate solution therefor the charge is changed. I will ensure the following variables are kept constant:
Concentration and amount of copper sulphate solution.
Voltage - At 2 volts direct current.
Time - Each test will run for 10 minutes.
Temperature - The experiment will take place at room temperature.
From my results I can conclude that as the charge is increased the amount of copper deposited at the cathode is increased. My results show that the relationship is directly proportional. For example if you double the 600C charge the mass of copper deposited is also doubled indicating the directly proportional relationship. Therefor my results support my prediction. With my scientific explanation and information I can make a table that shows the results that Faraday would have obtained from his laws.
Observing my results and Faraday’s results, they are not exactly the same but are very similar and both show the directly proportional relationship. Therefore my experiment can support Faraday’s findings.
Results of Faraday’s Law
I believe that my experiment was very successful and was easily carried out. There were no outstanding anomalies, however if I repeated this experiment again I would use new electrodes and clean them more efficiently with distilled water and wire wool aswel as propanone. Which would give me a more accurate measure of the cathode mass. Also as the experiment was took out in a lesson, time was limited therefor I would connect the electrodes for a longer period of time to the circuit so the charge would be increased therefor the amount of copper deposited would increase giving me more accurate results. Also I would weigh both electrodes to observe how much weight the anode loses, and see if the loss of weight would be proportional to the charge.
Here's what a star student thought of this essay
Quality of writing
The method is used with 'I' and should be non-personal to appear more professional in scientific manner. Otherwise, spelling, grammar and punctuation are good throughout. The layout of the piece is done well with clear well define subheadings.
Level of analysis
The diagram is easy to read and clearly set out. The candidate does not state what effect changing other variables will have on the experiment or why they have kept the variables constant which would have showed deeper understanding of the principles behind the experiment. The prediction and scientific background to it is done very well with good scientific depth and understanding showed. The apparatus is explained clearly with function so anyone reading could repeat the experiment themselves. Decimal places are inconsistent in the table and they should be kept consistent in order to make their calculations later more accurate. Their improvements and analysis of results is also done very well.
Response to question
The experiment is laid out very well. The candidate shows deep analysis of and focus on the question which leads to a well thought out experiment. A graph to display their results would have been a different format to display and interpret results from. The candidate could have gone into greater depth about other factors which may have affected the experiment and have accounted for them to increase their level.