I have chosen to do electrolysis of Copper Sulphate with copper electrodes rather than the alternatives, sulphuric acid with graphite electrodes, because then I would have to collect gas (which is more difficult) rather than a solid.

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Chemistry Coursework - Plan

I have chosen to do electrolysis of Copper Sulphate with copper electrodes            rather than the alternatives, sulphuric acid with graphite electrodes, because then I would have to collect gas (which is more difficult) rather than a solid.

Initial Aim

To find out how a change in current that passes through a copper sulphate solution changes the amount of product at the cathode. This is what I intially investigated in my preliminary experiment. I found out that this was was more problematic than verying time would be because when the current got higher the temperature within the circuit changed and as a result the current was not constant. I decided that time would be much easier to vary.

New Aim

To find out how the amount of time for which a current passes through a copper sulphate solution changes the amount of product at the cathode.

Hypothesis

I think that the increase in time for which current passes through the copper sulphate solution will be directly proportional to the amount of copper produced at the cathode and directly proportional to the amount of copper reduced from the anode. This follows exactly with Faraday’s first law or electricity and chemistry: ‘The mass of any element deposited during electrolysis is directly proportional to the number of coulombs of electricity passed’. I also predict that a small amount of sludge will be deposited at the bottom of the beaker.

Variables

The following variables are ones that could possibly be used:

∙ Time

∙ Current

∙ Temperature

∙ Concentration of Copper Sulphate solution

∙ Quantity of solution        

∙ Surface area of the copper electrodes in the Copper Sulphate solution

∙ Distance between the copper electrodes

I have chosen to vary the time and not the current because when varying the current the heat in the resistor changes, thus changing the resistance and the current. This would make the experiment akward because the current needs to be constant for each reading and do that the resistance may have to be altered throughout that particular reading. Vary time also enables me to keep all other possible variables constant more easily.

Apparatus

∙ Powerpack (set at 4 volts)

∙ Variable resistor

∙ Ammeter

∙ Copper plates (electrodes)

∙ Beaker

∙ The necessary connecting cables

∙ A rest with crocodile clips to hold the electrodes in the solution

I am using a variable resistor so that I can set the current and alter it should the circuit heat up, create more resistance and change the current. I am using the ammeter to make sure that the current is constant for each individual reading.

Diagram

Fair Test

To make it is a fair test a will keep all possible variables other than time constant. The current will be kept constant usind the variable resistor and kept track of using the ammeter. The temperature should remain constant as the current is constant throughout. The same solution will be used for each reading so that there is no change in quantity. The distance between the electrodes will be constant because the rest that holds the electrodes has crocodile clips which are spaced and fixed. In order for the surface area of the electrodes submerged in the solution to be constant I will clip them in the same place each time. This will be the most difficult to keep constant is is most likely to have error.

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Method

I poured 200ml of Copper Sulphate solution into a beaker. I got two copper strips to use them as electrodes and cleaned them thoroughly using sandpaper. I then weighed the two electrodes and recorded them so I could compare their weights after the experiment. These electrodes were then put into the beaker of copper sulphate, and then they were connected up to an ammeter and a power pack. A consistent current of 0.54 amps (the variable resistor would not allow a lower current) was passed through the solution. If I had used a higher current then too much ...

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