Required Practical: Electrolysis of Aqueous Solutions (AQA GCSE Chemistry: Combined Science)

Objective

To investigate what happens when aqueous solutions are electrolysed using inert electrodes

Hypothesis

A metal will be produced at the negative electrode because metal ions are positive

Materials

• Test tubes
• Electrolyte solutions
• 100 cm³ beaker
• Stand and clamp
• Two carbon rod electrodes
• Two crocodile / 4 mm plug leads
• Low voltage power supply
• Blue litmus paper

Electrolytic cell 

Diagram showing the electrolysis of aqueous solutions

Practical Tips

1. Make sure the test tubes do not cover the electrodes completely and fall to the bottom of the cell or the conductivity will fall considerably and the rate of electrolysis will be very slow
2. Replacing the test tubes with graduated test tubes or measuring cylinders means that the volume of gas produced over time can be measured

Method

1. Set up the apparatus as shown in the diagram
2. Add the aqueous solution to the beaker
3. Add two graphite rods as the electrodes and connect this to a power pack or battery
4. Turn on the power pack or battery and allow electrolysis to take place
5. Record the results in a suitable table (see below) and repeat for another solution, checking the electrodes in between runs to see if any metal has been deposited
6. The following aqueous solutions are suitable for this investigation: copper chloride, copper sulfate, sodium chloride, sodium bromide, sodium nitrate
7. The gases produced can be collected in the test tubes to be tested later

Results: Record your results in a suitable table:

Electrolysis of aqueous solutions table

Electrolyte	Observations at anode & gas test results	Observation at cathode & gas test result
Aqueous sodium nitrate, NaNO3	Effervescence, no colour, splint relights so gas is oxygen	Effervescence, no colour, squeaky pop, so gas is hydrogen

 

Evaluation

The gases and corresponding tests are:

• Hydrogen – lighted splint goes out with a squeaky pop
• Oxygen – a glowing splint relights
• Chlorine – damp blue litmus paper turns red and is then bleached white

Conclusion

Describe how the results obtained compare with the expected results based on the hypothesis