Water electrolysis with bases

This experiment shows the electrolysis of water using a different redox reaction. By changing the pH of the solution the reactions differ, although the results are the same.

In the basic environment there are OH – ions and Na+ ions, which migrate respectively towards the anode and cathode.

At the cathode, water molecules are reduced because their potential ( E0( H2O / H2 ) = – 0.83 V ) is greater than that of the sodium ions ( E0(Na / Na+ ) = – 2.73V ).Sodium ions will not undergo any reduction due to their very negative reduction potential.

At the anode OH – ions are oxidised because their potential (E0( O2 / OH ) = + 0.40 V) is lower than the potential of the redox couple ( E0( O2 / H2O ) = +1.23 v).

At the cathode (–) 4 H2O + 4 e – → 2 H2 + 4 OH –.

At the anode (+) 4 OH – → O2 + 2H2O + 4 e –.

• U tube with side outlets — 1276.10
• Platinum electrodes — 4716.12
• Connecting wires, red — 2522.03-04
• Connecting wires, black — 2522.04-08
• DC power supply

• Sodium hydroxide 0.2 M — R:35 S:26-37/39-45

• Always wear protective goggles and gloves.
• Hydrogen and air mixtures are explosive. Make sure there are no naked flames near the apparatus.

• Describe what happens in the apparatus.
• Write the balanced equations of the process and record your observations.
• What happens on igniting the test tubes? State where hydrogen and oxygen are produced.
• What are the differences between electrolysis in a basic and an acidic environment?