Investigation to show how the amount of electric current affects the amount of copper deposited at the electrodes during the electrolysis of copper sulphate solution using copper electrodes.

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Investigation to show how the amount of electric current affects the amount

of copper deposited at the electrodes during the electrolysis

of copper sulphate solution using copper electrodes

by Mohammed Bakir

Aim: I aim to investigate how the amount of electrical current affects the amount of copper deposited in the electrolysis of copper sulphate solution using copper electrodes.

Hypothesis: Electrolysis is the decomposition of a molten or aqueous compound by electricity. The compound decomposed during electrolysis is called an electrolyte. The energy which causes the chemical changes during electrolysis is provided by an electric current. It is important to remember that an electric current is simply a flow of electrons. When an electric current passes through the electrolyte, electrolysis takes place.

During electrolysis:

  • a metal or hydrogen forms at the negative cathode. This confirms that metals and hydrogen have positive ions. These ions are called cations because they are attracted to the cathode.
  • a non-metal (except hydrogen) forms at the positive anode. This confirms that non-metals (except hydrogen) have negative ions. These ions are called anions because they are attracted to the anode.

The experiment which I am to carry out involves an electrolyte of copper sulphate solution and electrodes made of pure copper. I am to investigate how the amount of electric current affects the amount of copper deposited at the electrodes during the electrolysis of the copper sulphate solution using the copper electrodes. I have already explained that the copper will form at the negative cathode as metals have positive ions.

When an electric supply is connected to the electrolytic cell, electrons flow from the anode to the battery and from the battery to the cathode. This is why the anode is positive as electrons have been drawn from it, and why the cathode is negative as electrons are given to it. As the electrolyte is of course an ionic compound, it contains positive and negative ions. As I have stated above, the copper ions are positive and are therefore attracted to the cathode. When the copper ions reach the cathode, they are discharged by the plentiful electrodes being put into the cathode. Thus they become copper atoms. This is shown by the equation:

Cu²+  + 2e- → Cu

This shows that two electrons are needed to discharge each copper ion.

In addition to the copper in the copper sulphate solution being decomposed, positive copper ions from the positive anode are also being attracted to the negative cathode. Therefore, positive copper ions are released from the anode into the copper sulphate solution. In effect, the copper anode is constantly supplying the electrolyte with copper which is then in turn discharged and deposited at the cathode. This means that electrolysis will not cease until the copper anode immersed in the electrolyte is completely decomposed in which case the electric current stops flowing as the anode is no longer connecting the rest of the circuit to the electrolyte. Thus the electrolyte will never go clear and lose all its copper and sulphur and oxygen.

I predict, therefore, that increasing the amount of electric currents flowing through the copper sulphate solution electrolyte will increase the amount of copper deposited at the cathode and increase the amount of copper released from the anode. Similarly, decreasing the amount of electric current will decrease the amount of copper deposited at the cathode and decrease the amount of copper released from the anode.

This is because, if the electric current is greater, more electrons are being supplied to the cathode and more taken from the anode which means that copper ions can be discharged at a quicker rate at the cathode as there are more electrons, and that more copper ions can be supplied to the electrolyte by the anode as more electrons are being taken away from it. Similarly, if the electric current is smaller, fewer electrons are being supplied to the cathode and fewer taken from the anode.

Michael Faraday was one of the first scientists to study electrolysis. His first law of electrolysis states that the mass of a given element liberated during electrolysis is directly proportional to the quantity of electrical current consumed during electrolysis. This supports my predictions entirely.

Here is a diagram to show what happens during the electrolysis of copper sulphate solution using copper electrodes:

Method: I will conduct an experiment in order to find out whether my prediction is correct or not. In order to conduct this experiment, I will need a beaker containing 80cm³ of copper sulphate solution, two copper strips (electrodes), an ammeter, a rheostat, a stop-watch, a power-pack, crocodile clips, distilled water, propanone, a hairdryer and an electronic weighing machine.

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The apparatus will be set up as shown below:

Before connecting the copper electrodes to the circuit, I will weigh them both with the electronic weighing machine in order to enable me to compare the weights of the electrodes after electrolysis with the weights before electrolysis. By comparing these weights, I will be able to work out the change in weight and thus find out how much copper has been deposited at the cathode and how much has ...

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