Separate water into hydrogen and oxygen

How to separate water into hydrogen and oxygen?

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Separate water into oxygen and hydrogen


You might wondered how to separate water into hydrogen and oxygen. Maybe you even thought how to produce oxygen aboard a submarine . This lesson is for you!

This experiment is related to electrolysis of water. Using battery and copper wire, we can split water into hydrogen and oxygen. What is more interesting we see that flame is brighter whenever we are getting our candle closer to pure oxygen. Therefore, it is a fantastic introduction of science and physics for preschoolers.

After all, please leave your comments below. I am curious how it goes for you.

In our experiment we used:

  • Water
  • Copper wire
  • Battery (9V)
  • Salt
  • Lighter

Experiment execution

Due to the fact that hydrogen and oxygen are very reactive and flammable, please take special precautions:

  • work in distance from flammable things (wood, LPG kitchens, papers, curtains and so on)
  • be ready to fade out potential fire
  • use glasses at all time
  • keep your hair tied up
  • do not breath the gases (especially chlorine)

Step 1 – Prepare container

Firstly, take a water container. We prefer the flat one because it is easier to manipulate with copper wires and a candle. Additionally, flat container is more stable and therefore more secure.

Step 2 – Pour the water and add salt

In the step 2 we take water and fill the container with it. We are adding kitchen salt into the water as a result your water and salt solution should be around 10%. In conclusion it means following proportions: 90 grams of water and 10 grams of salt. For your convenience we prepared a table so you can quickly adjust the amounts.

Amount of water (g)Amount of salt (g)

Step 3 – Prepare the battery and wires

Now the electric part. Prepare 9V battery (the cuboid one). To be honest it can be whatever shape you like, but this one stands firmly and it is relatively easy to connect the copper wires into it. In addition to that, prepare two separate strings of a copper wire, ca. 30 cm each. They need to be long enough so you can make a firm connection with the battery, make twirled ends that go into the water and salt solution and hang them over the container.

Make sure that they are long enough so when in the water, you can keep the distance between them. In other words, the ends of the wires cannot touch each other.

Step 4 – Connect the wires to the battery

Above all, to make the experiment go, we have to connect the wires to the battery. As a result, one string of wire goes into the “+” and the other string is connected to “-“.

Step 5 – Place the wires in the water container

Now the best part. Once you place the wires into the water reaction starts immediately. Due to the electric current you can observe bubbles (hydrogen, oxygen) and kind of blue/green substance (chlorine).

Step 6 – Observe the results

Congratulations! You have just made a simple generator of oxygen and hydrogen. In addition, you can check the reaction of oxygen / hydrogen with a candle. Therefore, lit a candle and gently get closer and closer over the place where bubbles are coming out from the water. What do you see? Is the light lighter?

Please leave your comments below. I am curious how it goes for you.

Explanation for pros

Why the electrolysis of salted water happens?

In pure water at the negatively charged cathode, a reduction reaction takes place, with electrons (e) from the cathode being given to hydrogen cations to form hydrogen gas. The half reaction, balanced with acid, is:
Reduction at cathode: 2 H+(aq) + 2e → H2(g)

At the positively charged anode, an oxidation reaction occurs, generating oxygen gas and giving electrons to the anode to complete the circuit:
Oxidation at anode: 2 H2O(l) → O2(g) + 4 H+(aq) + 4e

Is it possible to split pure water during electrolysis?

Electrolysis of pure water requires excess energy in the form of overpotential to overcome various activation barriers. Therefore without the excess energy the electrolysis of pure water occurs very slowly or not at all. This is in part due to the limited self-ionization of water. In addition, pure water has an electrical conductivity about one millionth that of seawater.
Electrolyte-free pure water electrolysis has been achieved by using deep-sub-Debye-length nanogap electrochemical cells. When the gap distance between cathode and anode even smaller than Debye-length (1 micron in pure water, around 220 nm in distilled water), the double layer regions from two electrodes can overlap with each other, leading to uniformly high electric field distributed inside the entire gap.


Interesting facts

As a interesting fact water electrolysis is used widely aboard a submarines. Similarly to our experiment it goes in two steps. Firstly, using the electricity generated aboard , first step to provide oxygen is to make pure water from sea water: desalinization. This is done by an evaporator/distiller or reverse osmosis process. Secondly, the pure water (H2O) is then used to create an oxygen supply, using the electrolysis method.


Water electrolysis or in other words split of water into oxygen and hydrogen can be a nice experiment but please take precautions so your children have fun and good memories. If you liked the bubbles, you might like also my other experiment where I play with carbon dioxide (gas form). Please check my post How to make dancing grapes?

Please leave the comment below. We are curious what are your suggestions and results.


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