Core practical - electrolysis of Copper Sulfate solution

To investigate the electrolysis of copper sulfate solution using inert (unreactive) **electrodes**:

* Pour some copper sulfate solution into a beaker.


* Place two graphite rods into the copper sulfate solution. Attach one electrode to the negative terminal of a dc supply, and the other electrode to the positive terminal


* Completely fill two small test tubes with copper sulfate solution and position a test tube over each electrode


* Turn on the power supply and observe what happens at each electrode


* Test any gas produced with a glowing splint and a burning splint.


* Record your observations and the results of your tests.

What will the observations/results be?

Negative Electrode: A Brown/pink solid forms (copper)

Positive Electrode: Water and Oxygen (colourless gas forms)- test using glowing splint

Suggest an explanation for why it may be difficult to obtain positive results for the tests on gases.

The volumes of gas collected are very small, making it difficult to carry out the tests.

Copper electrodes take part in the reactions and are described as non-inert. Why are they non-inert?

Involved in the reaction:

* at the positive electrode, copper **atoms** lose **electrons** and form copper **ions**, Cu2+
* at the negative electrode, copper ions gain electrons and form copper atoms

Describe the process used industrially to purify copper

Use non-inert copper electrodes in copper sulfate solution.

Describe an investigation on the effect of current on the mass of copper lost and gained from 2 copper electrodes:

* Pour some copper sulfate solution into a beaker
* Measure and record the mass of a piece of copper foil. Attach it to the negative terminal of a dc supply, and dip the copper foil into the copper sulfate solution.
* Repeat step 2 with another piece of copper foil, but this time adjuntar it to the positive terminal.
* Make sure the electrodes do not touch each other, then turn on the power supply. Adjust the power supply to achieve a constant current as directed by your teacher.
* After 20 minutes, turn off the dc supply.
* Carefully remove one of the electrodes. Gently wash it with distilled water, then dip it into propanone. Lift the electrode out and allow all the liquid to evaporate. Do not wipe the electrodes clean. Measure and record the mass of the electrode.
* Repeat step 6 with the other electrode. Make sure you know which is which.
* Repeat the experiment with fresh electrodes and different currents.

\
Record the currents used and the masses of each electrode in suitable tables

\
Plot info on a graph- draw line of best fit to see proportionality

\
Conclusion:

The gain in mass by the negative electrode is the same as the loss in mass by the positive electrode. So the copper deposited on the negative electrode must be the same copper ions that are lost from the positive electrode.