Electrolysis of Water

About this simulation

This simulation shows the electrolysis of water. Students set the voltage from 0 to 12 V and the electrolyte concentration, and watch hydrogen collect at the negative cathode and oxygen at the positive anode. Nothing happens below about 1.5 V. Time runs 20 times faster than real so the tubes fill in seconds, and a button empties them for a new run. Readouts show current, hydrogen and oxygen gas and the H2 to O2 volume ratio. It is a clear way to teach decomposition, the electrodes and why hydrogen volume is double that of oxygen.

What students can explore

Raise Voltage from 0 and note the point near 1.5 V where gas first appears and Current becomes non-zero.
Compare Hydrogen gas and Oxygen gas and check that the H2 : O2 volume ratio is about 2 to 1.
Double Electrolyte concentration and see how the Current changes.
Press Empty tubes and refill at 12 V and 3 V to compare how long each takes.
Identify which electrode produces which gas and write the half equations.

Learning objectives

1Describe electrolysis as the decomposition of water by direct current.
2Identify the products at the cathode and the anode.
3Explain why hydrogen is produced in twice the volume of oxygen.
4Describe how voltage and concentration affect the current and the rate of gas production.

Questions teachers ask

Is it free?

Yes. It is free, runs in any modern browser including interactive whiteboards and tablets, and needs no sign-up or installation.

Why is there twice as much hydrogen as oxygen?

Water is H2O, so splitting it gives two hydrogen atoms for every oxygen atom. The balanced equation 2H2O gives 2H2 plus O2, and equal volumes of gas hold equal numbers of molecules, so the ratio is 2 to 1.

Which gas forms at which electrode?

Hydrogen forms at the negative cathode and oxygen forms at the positive anode. Electrons enter the water at the cathode and leave at the anode.

How do I use it in class?

Move the Voltage and Electrolyte sliders and read the current and gas values. Press Empty tubes to start a new run, and ask students to predict how long the tubes will take to fill.

Embed this simulation

Drop it into your LMS, blog, or class site — free.

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