Obtain an oxyhydrogen mixture from water electrolysis

20 minutes
Experiment's video preview



  • Put on protective gloves and eyewear.
  • Conduct the experiment on the plastic tray.
  • Keep a bowl of water nearby during the experiment.
General safety rules
  • Do not allow chemicals to come into contact with the eyes or mouth.
  • Keep young children, animals and those not wearing eye protection away from the experimental area.
  • Store this experimental set out of reach of children under 12 years of age.
  • Clean all equipment after use.
  • Make sure that all containers are fully closed and properly stored after use.
  • Ensure that all empty containers are disposed of properly.
  • Do not use any equipment which has not been supplied with the set or recommended in the instructions for use.
  • Do not replace foodstuffs in original container. Dispose of immediately.
General first aid information
  • In case of eye contact: Wash out eye with plenty of water, holding eye open if necessary. Seek immediate medical advice.
  • If swallowed: Wash out mouth with water, drink some fresh water. Do not induce vomiting. Seek immediate medical advice.
  • In case of inhalation: Remove person to fresh air.
  • In case of skin contact and burns: Wash affected area with plenty of water for at least 10 minutes.
  • In case of doubt, seek medical advice without delay. Take the chemical and its container with you.
  • In case of injury always seek medical advice.
Advice for supervising adults
  • The incorrect use of chemicals can cause injury and damage to health. Only carry out those experiments which are listed in the instructions.
  • This experimental set is for use only by children over 12 years.
  • Because children’s abilities vary so much, even within age groups, supervising adults should exercise discretion as to which experiments are suitable and safe for them. The instructions should enable supervisors to assess any experiment to establish its suitability for a particular child.
  • The supervising adult should discuss the warnings and safety information with the child or children before commencing the experiments. Particular attention should be paid to the safe handling of acids, alkalis and flammable liquids.
  • The area surrounding the experiment should be kept clear of any obstructions and away from the storage of food. It should be well lit and ventilated and close to a water supply. A solid table with a heat resistant top should be provided
  • Substances in non-reclosable packaging should be used up (completely) during the course of one experiment, i.e. after opening the package.

FAQ and troubleshooting

How many times can I fill the bottle with gas and try to blow the candle out?

Many times, actually. Try it out!

The candle didn’t go out. What should I do?

Well, you can repeat steps 3 and 4 many times. Try again! Try running the electrolysis a bit longer to let more gas accumulate. You can also change the angle from which you point the bottle at the candle.

The cable plug turned green. Why?

The cable plug has some metal parts made of copper. When oxidized, copper often turns green.

The solution is leaking from the pipette! What should I do?

If this happens, first disconnect the battery holder from the electrolyzer. Then, carefully separate the cable plug from the pipette. You need to fix the leak. Some tape or even a piece of your protective glove should work well. Wrap your material of choice around the cable plug and insert it into the pipette again. Once you’re sure the leak has stopped, continue with your experiment.

Step-by-step instructions

Prepare the setup for water electrolysis. This setup is called an electrolyzer.


Now fill the electrolyzer halfway with sodium hydroxide NaOH solution.


Set up the vial to collect oxyhydrogen gas and start the process of water electrolysis.


Now try to extinguish the candle by means of the reaction between hydrogen and oxygen.


To repeat the experiment, connect the electrolyzer to batteries and repeat steps 3 and 4.

Expected result

When electrolyzed, water decomposes into two gases: oxygen O2 and hydrogen H2. The end result is twice as much hydrogen as oxygen. Such a mixture of gases is called oxyhydrogen. When a bottle full of oxyhydrogen is placed near a burning candle, the gas ignites immediately and blows out the candle.


Dispose of solid waste together with household garbage. Pour solutions down the sink. Wash with an excess of water.

Scientific description

Why do the contents of the bottle burst?

The chemical formula of a water molecule is H2O, which means that it consists of two hydrogen atoms and one oxygen atom. The bottle contains a mixture of two parts gaseous hydrogen and one part gaseous oxygen. When this mixture is ignited, the immediate reaction of water formation takes place with a characteristic “pop!” sound. The water vapor formed in this reaction blows the candle out.

Learn more

Chemically, the process of water formation looks rather simple:

2H2 + O2 → H2O

However, it is not as simple as it seems. This is a reduction-oxidation reaction, with oxygen being an oxidizer (taking electrons from hydrogen) and hydrogen being a reducer (giving its electrons to oxygen):

O2o + 4e → 2O2-

H2o - 2e → 2H+

This reaction proceeds vigorously, especially when oxygen is mixed with hydrogen in a 1:2 ratio as it is in our experiment. This is because the resulting product, water vapor, contains one oxygen atom and two hydrogen atoms - the ratio is also 1:2.

How do oxygen and hydrogen get into the bottle?

These gases are the product of electrolysis - the process in which we use electricity to split water into oxygen and hydrogen. During electrolysis, oxygen and hydrogen gases form in a 1:2 ratio, comprising a mixture called oxyhydrogen, which bursts in the experiment.

How does electrolysis occur?

First of all, this process requires a basic medium. We create these conditions by adding sodium hydroxide NaOH. When in a liquid state, water can split into ions:

H2O → H+ + OH-

The basic medium increases the concentration of hydroxide ions OH-. An electrolyzer (the device for water electrolysis) has a positively charged anode, which attracts anions, and a negatively charged cation, which attracts cations. So H+ cations migrate to the cathode and OH- anions to the anode. Then H+ ions take electrons from the cathode and turn into hydrogen H2, while hydroxide ions OH- give their electrons to the anode and turn into oxygen O2.

In our experiment, the electrolyzer is made from an RCA plug, with its metallic ring being a cathode while the pin is an anode. However, one can change the poles by connecting the wires of the plug and the battery holder the other way round - this will not affect the experiment.

What is an RCA plug?

The RCA plug was once widely used for audio and video systems. It could connect, for example, a video player with a TV set. It is still used for some visual equipment but is not so widespread anymore. It consists of two metallic parts, an outer ring and a pin, with a plastic insulating ring between them. Separate wires are connected to each of the metallic parts: the shorter wires are connected to the metallic ring, while the longer wires connect to the pin.