It is important in this practical activity to use appropriate apparatus safely to carry out electrolysis, and to use appropriate techniques to identify gases.
This outlines one way to carry out the practical. Eye protection must be worn.
Copper(II) sulfate solution
1. Pour some copper(II) sulfate solution into a beaker.
2. 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.
3. Use a dropping pipette to completely fill two small test tubes with copper(II) sulfate solution. Quickly turn each test tube upside down, keeping its mouth under the surface of the copper(II) sulfate solution. Position a test tube over each electrode. Rinse any copper sulfate solution off your hands.
4. Make sure the electrodes do not touch each other, then turn on the power supply. If no bubbles are observed, check all the electrical connections and the dc supply.
5. Continue to collect any gases in the test tubes, then turn off the dc supply.
6. Oxygen should be produced at the positive electrode. Confirm this by holding a glowing splint just inside the open mouth of its test tube. Record whether the splint relights.
Sodium chloride solution
7. Repeat steps 1 to 5, but using sodium chloride solution instead of copper(II) sulfate solution.
8. Hydrogen should be produced at the negative electrode. Confirm this by holding a lighted splint near the open mouth of its test tube. Record whether a squeaky pop is obtained.
9. Chlorine should be produced at the positive electrode. Confirm this by holding a piece of damp blue litmus paper just inside the open mouth of its test tube. Record whether this turns red then white.
Record what happens at each electrode, including the results of the gas tests.
Identify the gases produced during the two experiments.
Name the brown substance produced at the negative electrode during the electrolysis of copper(II) sulfate.
The brown substance was copper.
Suggest an explanation for why it may be difficult to obtain positive results in the tests for gases.
The volumes of gas collected are very small, making it difficult to carry out the tests.
Evaluate the hazards and the precautions needed to reduce the risk of harm. For example:
|Hazard||Possible harm||Possible precaution|
|Copper(II) sulfate solution||Harmful through skin contact and can cause serious eye irritation||Wear gloves, wear eye protection and rinse hands after contact|
|Chlorine gas||Toxic if inhaled||Make sure the lab is well ventilated and avoid inhaling the gas and do not run the experiment longer than is necessary to collect a sample|
|dc electricity supply||Electric shock||Make sure electrodes do not touch and make sure that electricity supply is switched off before handling apparatus|