Required Practical: The Electrolysis of Aqueous Solutions

Aim

Investigating the effects of electrolysis on aqueous solutions using inert electrodes.

Hypothesis

  • A non-metal will be produced at the positive electrode because non-metal ions are negatively charged.
  • A metal will be produced a the negative electrode, as metal ions are positively charged.

Apparatus

To perform this experiment, we will need the following apparatus:

  • Test tubes (for gas collection)
  • A 100 cm3 beaker
  • A low-voltage power supply
  • Electrolyte solutions
  • Two crocodile/4mm plug leads
  • Two carbon rod electrodes
  • Blue litmus paper
  • Matches or splints

Method

1. Use a measuring cylinder to add the aqueous solution to the beaker

2. Place the two graphite rods (the electrodes) into the aqueous solution

  • Attach one electrode to the negative terminal of a dc supply and attach the other electrode to the positive terminal

3. Place a test tube over each electrode to collect the gases

4. Turn on the power supply and allow electrolysis to take place

It is important to take necessary safety precautions while performing this experiment, such as wearing goggles and gloves. Also, ensure the proper disposal of the electrolyte solutions after the experiment is completed.

Identifying the gases

Hydrogen – Place a lighted splint in the test tube containing the gas. If it contains hydrogen, then the splint will go out and there will be a squeaky pop.

Oxygen – Place a glowing splint in the test tube containing the gas. If it contains oxygen, then the splint will relight.

Chlorine – Place damp blue litmus paper in the test tube. If it contains chlorine, the litmus paper turns red and then it is bleached white.

Results

Record your results in an appropriate table. For example:

ElectrolyteObservation at negative electrode, including gas test resultsObservation at positive electrode, including gas test results
Dilute sodium chlorideEffervescence, no colour, lighted splint goes out with a squeaky pop Hydrogen gasEffervescence, pale green gas, blue litmus paper turns red then white Chlorine gas

Conclusion

Compare your experimental results with the expected outcomes from your hypothesis. For example, mention if your hypothesis is supported by the observation. If your results do not match the hypothesis, discuss possible sources of error or factors that may have influenced the outcome.