Electrolysis of Water
Split water into hydrogen and oxygen and watch the bubbles collect in a 2:1 ratio.
Anode (+), oxidation: 2 H₂O → O₂ + 4 H+ + 4 e−
Overall: 2 H₂O → 2 H₂ + O₂
About the Electrolysis of Water
Free electrolysis simulation. Apply a voltage across water, watch hydrogen and oxygen bubbles form at the electrodes, and see the 2:1 gas volume ratio and the half-reactions. Built for electrochemistry, the electrolysis of water runs instantly in your browser: change a setting or drag an object and the result updates at once, so you learn by trying things out rather than only reading about them.
Split water into hydrogen and oxygen and watch the bubbles collect in a 2:1 ratio. Use it to explore electrochemistry ideas at your own pace, then check what you found against the key ideas further down this page.
How to use the Electrolysis of Water
- Use the controls to change Voltage, Dissolved salt (conductivity). The simulation reacts instantly.
- Press "Switch on", "Empty tubes" to start, reset or change what is happening.
- Where you see a glowing handle, object, weight or atom, drag it with your mouse or finger. Everything responds in real time.
- Watch the readouts and graphs update as you experiment, and compare what you see with the key ideas below.
Things to try
- Raise the voltage.
- Add salt.
- Compare H₂ and O₂ volumes.
- Find the minimum voltage.
Key ideas you can learn
- Electrolysis uses electrical energy to force a non-spontaneous reaction.
- At the cathode water is reduced to H₂, and at the anode it is oxidised to O₂.
- Twice as much hydrogen gas forms as oxygen: 2 H₂O → 2 H₂ + O₂.
Where this is used in the real world
Electrolysis produces hydrogen fuel, chlorine, aluminium and pure metals, and is used in electroplating and water treatment.
Who is this simulation for?
Chemistry students studying redox, batteries and electrolysis, and teachers who want a clear picture of where the electrons go.
For teachers: project it on the board, let students predict what will happen, then run it together. For students: change one thing at a time and write down what changes.
Frequently asked questions
Why is there twice as much hydrogen as oxygen?
Water is H₂O, so splitting 2 H₂O gives 4 hydrogen atoms (2 H₂) and 2 oxygen atoms (1 O₂). Equal amounts of gas means twice the volume of hydrogen.
What is the difference between a galvanic and an electrolytic cell?
A galvanic cell makes electricity from a spontaneous reaction. An electrolytic cell uses electricity to force a non-spontaneous reaction.
Is the Electrolysis of Water free to use?
Yes. It is completely free, with no signup, no download and no ads inside the simulation. It runs in your web browser.
Does the Electrolysis of Water work on a phone or tablet?
Yes. It uses touch as well as the mouse, so you can drag objects with your finger. A larger screen makes the controls easier to see.