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Wires- this will be used to join the circuit up.
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Weighing scale- this will be used to weigh the cathode each time.
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Sand Paper- this will be used to scrap off any impure copper.
Scientific Knowledge:
When copper is extracted from the ore it is about 98% pure so electrolysis is used to make the copper more purer. Electrolysis is used in big industries to get metals purified. As they want the metals 100% pure.
What is electrolysis?
Electrolysis is the procedure, which is used for the electricity to decompose a compound. The substance must be in a form of liquid or molten to allow the movement of the particles. This means that the solution must be electrolyte.
In the electrolysis of cupper (ii) electrodes and copper sulphate solution, the copper ions at the anode give ions to the cathode. That means that how much the anode has lost the cathode should have gained. The anode is positively charged ions, and the cathode are negatively charged ions. The ions in the anode are called the anions, and in the cathode they are called the cations.
From my research I have found out that in the 1830’s a famous scientist called Michael Faraday was the first to find out about electrolysis. Therefore the Faraday’s first law says:
The quantity of electricity passed is proportional to the amount of substance discharged at an electrode.
The amount of electricity that flows is measured in coulombs (C). I have also learned that every one amp of current passes one coulomb of charge every second. Therefore the equations for this is:
Quantity of electricity (charge)=current X time
Coulombs= amps X seconds
I have found out that as the electric current passes through electrolyte solution, the chemical reaction will take place at both the cathode and anode.
The equations for the reaction with copper(ii) plates and copper sulphate solution are:
Ions present: CuSO4 Cu2+ + SO42-
At cathode (-): Cu2+ ions are attracted
Cu2+ + 2e- Cu : this is a reduction reaction.
At anode (+): The atoms of the copper lose two electrons and dissolve into the solution.
Cu - 2e- Cu2+ : this is a oxidation reaction
The time that you let the electric current pass through the circuit could effect on how much copper is deposited at the cathode. The longer you let the circuit run for the more copper will be deposited.
The amount of current, which flows though, the circuit will increase. Electric current however only flows when the charges can move freely. Also my making the voltage higher the current will increase. The resistor is there to change the flow of current that we are measuring. Therefore I will now make a prediction:
As the current increases the amount of copper deposited will also increase.
The more copper will be deposited, as more electrons will flow through the circuit. This speeds up the rate of reaction.
Also the quantity of solution will effect how much copper is deposited at the cathode. As the electrodes will go into the solution more deeply so more ions will be acting on it. In the electrolyte there are many charged particles and this works towards how much copper is deposited.
Before caring out my investigation I have taken a preliminary study to see how the electrolysis works and what would be the best factor to chance. During this preliminary study I did not change any factors.
Method:
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Firstly I will use a measuring cylinder to measure out 150ml of copper sulphate solution.
- Secondly I will join up the circuit in a series circuit.
- Then using sand paper I will scrap off any copper deposited on the cathode and weigh it on the weighing scale, and make a note of this.
- I will place the cathode in the circuit and put the power pack on 2 volts.
- Then after I am going to stat my stop watch.
- After the 10 minutes I will dip the cathode in distilled water then, dipped it in Ethanol.
- Thereafter in the oven I will dry the cathode and weigh it.
- I will be repeating this procedure for 0.4A, 0.6A, 0.8A and 1.0A
Each experiment will be done at least three times.
Results:
Results:
I know that this is a straight line graph and that the gradient is positive by looking at the graph. I can now interpret from this graph that this investigation matches the law of Michel Faraday, the first law that I mentioned in the scientific background knowledge is:
The quantity of electricity passed is proportional to the amount of substance discharged at an electrode.
This law infant matches my results that I have gained, I can now confidently say that the results that I obtained were accurate. As I increased the voltage and the current there was a larger mass in the cathode. Therefore this proves that my prediction which I made is correct:
As the current increases the amount of copper deposited will also increase.
In this electrolysis both the oxidation and reduction reactions have been used, the oxidation in the anode and the reduction in the cathode.