Water electrolysis with acids
Electrolysis of water in acidic solution: a direct current drives redox reactions in the electrolyte, and the gases produced are collected.
The science behind this experiment
Electrolysis is a process which produces chemical changes due to the flow of a direct electric current through an electrolyte. When a current flows through a conducting solution, the ionic species undergo redox reactions.
2 H2O ↔ H3O + + OH –.
Adding sulphuric acid increases the conductivity by generating electrolyte as follows.
Direct Electric current causes the following reactions in the acidified water at the platinum electrodes.
At the cathode (–) 4H3O + + 4 e – → 2 H2 + 4H2O At the anode (+) 6 H2O → O2 + 4H3O + + 4 e –.
At the cathode H3O+ ions are reduced because their potential ( E0( H+ / H2 ) = + 0.00 v ) is greater than that of water molecules H2O ( E0( H2O / H2 ) ).
At the anode water molecules are oxidised because of their electrode potential ( E0( O2 / H2O ) ).
Equipment used
- U tube with side outlets — CHE-004
- Platinum electrodes — CHE-016
- Connecting wires, red — ELE-005, ELE-006
- Connecting wires, black — ELE-007, ELE-008
- DC power supply
Chemicals and reagents
- Sulphuric acid solution 0.1 M — R:35 S:26-30-45
Safety notes
- Hydrogen and air mixtures are explosive. Ensure that there are no naked flames near the apparatus.
Questions for students
- Describe what happens in the apparatus.
- What happens on igniting the test tubes? State where hydrogen and oxygen are produced.
- Why do we use a dilute acidic solution instead of distilled water?
What to expect
Passage of the electric current causes bubbling at the electrodes. The gas collected at the cathode (–) pops, indicating the presence of hydrogen. The gas collected at the anode (+) brightens up the flame indicating the presence of oxygen. At the cathode (–) H+ are reduced to hydrogen. At the anode (+) water molecules are oxidized to oxygen and H+ ions. Distilled water does not conduct electricity but the presence of some electrolyte allows an electrical current to flow as demonstrated in the previous experiments.
Disposal
Dispose of the solution into the waste container.
Run this experiment in your classroom
This experiment is part of ATP Volta — a self-contained mobile science lab that turns an ordinary classroom into a working STEM laboratory, with over 200 experiments in physics, chemistry, biology, robotics and engineering. Gali, the AI tutor built into ATP Connect, guides students through each step and answers their questions at the bench.
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