Investigate whether voltage affects the rate of electrolysis?

Coursework

By Duncan Shears 15/09/02

Aim:

To investigate whether voltage affects the rate of electrolysis?

Independent variables:

The voltage is going to be increased to see if it affects the rate of electrolysis and how much copper is transferred from the anode to the cathode. I will note down if, the rate of electrolysis grows with the increase in voltage and if so how much.

Dependent variables:

At each voltage I am noting down how quickly electrolysis occurs. To get results we must measure how much the cathode gains in weight and how much the anode loses. We must measure the weight of the electrodes before the experiment and after to see the increases in weight at the cathode and decrease at the anode

Controlled variables:

To ensure a fair test, the amount of copper sulphate must be kept the same. The time the experiment is done for must be kept the same for each voltage. I must use the same anode and cathode throughout the experiment.

Background information:

We have in the past gone through this experiment in class as demonstration from our teacher so that we knew what the experiment involved.

Hypothesis:

I predict that as I increase the voltage on the power pack so will the current in the current and this will pass on more electrons to the cathode, this will then increase the rate of electrolysis, hopefully. This will occur because electrical energy is bringing about a chemical change and the more electrical energy (current) that is going through the circuit the quicker the chemical change will happen. The weight of the cathode will increase and the anode will decrease in weight.

Apparatus

In the experiment we will need 200ml of Copper sulphate, 2 copper ...

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Hypothesis:

I predict that as I increase the voltage on the power pack so will the current in the current and this will pass on more electrons to the cathode, this will then increase the rate of electrolysis, hopefully. This will occur because electrical energy is bringing about a chemical change and the more electrical energy (current) that is going through the circuit the quicker the chemical change will happen. The weight of the cathode will increase and the anode will decrease in weight.

Apparatus

In the experiment we will need 200ml of Copper sulphate, 2 copper electrodes about 1cm wide and 7cm long, electronic leads with crocodile clips, a power pack, a beaker, a timer, an ammeter and a hair dryer.

Method:

First you get the beaker with 200ml of copper sulphate.
weigh the two pieces of copper (these are your electrodes) before starting so that you can compare it to the weights of them when the experiment has been completed after each voltage.
Put the two electrodes into the solution. (Make sure that at least one inch of copper is sticking out at the top so the crocodile clips don’t go into the solution and get coated in copper.
Link one to the positive slot in the power pack, this is now your
Link the other one to the negative side of the power pack, this is now your
The cathode should increase in weight as copper is added to it, and the Anode should decrease in weight as copper is taken from it.
Now switch the system on and the anode should dissolve because its atoms give up electrons to form ions: Cu Cu2+ 2e-, start the timer as soon as you turn on the current. The cathode should collect copper and the anode should lose it through Electrolysis.
After 5 minutes stop the timer and turn off the power supply and dry with the hair dryer and weigh the anode and cathode.
We will do this twice for each size voltage, 2, 4, 6, 8, and 12, to get an average until we have a set of results.

Safety:

Lab coats should also be worn as to not dye or get and liquid on your clothes. Goggles must always be worn to protect your eyes whilst using copper sulphate and whilst using any liquids. You should be careful also whilst handling wires and electricity.

Accuracy and reliability:

In my experiment I am doing a number of things to make my experiment as accurate and reliable as it can be. Firstly I will repeat the experiment twice for each voltage and with those results find an average that is more reliable than one result. I will also use electronic scales to weigh the amount of copper emitted to the anode and taken from the cathode to get and exact result. Next time I think I could use a different anode and cathode every time for each voltage to get very reliable results!

Obtaining evidence:

At first I was only going to do 1 set of readings for each voltage on the anode and cathode but I did 2 instead to get more reliable results.

I may have anomalous result in my result for 12 volts of current because there is a huge leap from the result for 10 volts to the result for 12 volts, which seems irregular but I have still decided to keep it in my graphs and results just to show that I have noted its existence

Analysing evidence:

These graphs proves to you that as the voltage is increased so does the rate of electrolysis. The graph shows you the weight of the cathode grew noticeably as the copper was taken from the anode and attracted to it. Also you can see from the second one that the weight of the anode decreased through the experiment as the metal was taken from the anode and added to the cathode. From 1.23 to 0.52 there is a clear decrease in weight on the anode, and an increase on the cathode.

Conclusion:

In conclusion my results have proved my prediction, as the voltage increased the faster electrolysis occurs, to be true. As the cathode grew in weight and the anode shrank in weight, which proves that electrolysis did actually occur.

Evaluation:

The results that I collected from this experiment

I may have had one anomalous result, which could have been a result of a concentration error or timing the experiment not for the 5-minute period.

I think I used good reliable equipment but to get a more reliable set of results could have changed the anode and cathode for each set voltage! I think I had a good range of results that displays my prediction and what I was trying to prove in the experiment.