Has associated hydrogen gas with bubbling

Water splitting

Experiment of the month February 2015

You need this:

  • 2 pencils
  • 1 9V battery
  • 1 glass half filled with water
  • ½ teaspoon of Glauber's substitute (sodium sulfate is available without a prescription in any pharmacy)

Thats how it works:
Water is a vital substance that also occurs in our body. It consists of tiny building blocks called atoms. Everything you see and what surrounds us consists of these small parts. There are compounds that are composed of several types of atoms, including water. Here it is the elements hydrogen and oxygen.

In the following experiment we split water into its two components.
First you need two pencils, which you sharpen at both ends.
Then you fill a glass half full with water and dissolve some Glauber's salt in it. The Glauber's salt serves here as an electrolyte. It is a substance that conducts electricity. Because pure water has only a very low conductivity.

One end of the two pencils are immersed in the water, while the other ends are brought into contact with the 9V battery (see picture).
You can now observe rising gas bubbles at both ends of the pencil. However, twice as many bubbles rise on the pencil, which is in contact with the negative pole of the battery, as on the positive pole of the battery.

What is happening?
Water has twice as many hydrogen atoms as oxygen atoms. These rise at the negative pole in the form of gas bubbles, because this is where the hydrogen is created. The same thing happens at the positive pole, where oxygen is formed. There are only half as many bubbles there. The current flow triggers a chemical reaction that converts water into hydrogen and oxygen.

The chemist Marc Ledendecker is a doctoral student at the Max Planck Institute for Colloids and Interfaces and is working on new catalysts for electrocatalytic water splitting.


proWissen e.V. and PotsKids present various experiments together with Potsdam scientists.