Fire foam

Ignite hydrogen soap bubbles!

20 minutes



  • Put on protective gloves and eyewear.
  • Conduct the experiment on the safety underlay.
  • Keep a bowl of water nearby while working with fire.
  • Keep flammable objects and hair away from the setup.
  • Remove protective gloves before lighting the splint.
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

Can I repeat this experiment with the liquid soap that I have at home?

Your kit contains two packets of liquid soap, so you should be able to perform this experiment twice. We don't recommend that you use your own liquid soap – it might prove difficult to measure the amount you need, and the result probably won’t be quite as impressive.

Why is it so important that the rubber stopper, metal cylinder, and tubing be securely connected?

This is necessary to keep the hydrogen contained. Otherwise, the gas will leak out and the foam won't form.

The NaHSO4 aggregated into lumps. How can I measure it?

Use a stirring rod from the set to break these lumps apart. Keep stirring the salt in the bottle until it becomes homogeneous.

The foam isn’t forming, or is forming very slowly. What should I do?

First of all, check that the hose is fit snugly into the rubber stopper, and the stopper is secured in the flask because there have to be no gaps for gas to leak through! Next, gently swirl the flask to mix the contents and wait a few more minutes. Try igniting the foam one more time.

Why don’t we take the tubing out when igniting the foam?

The tubing should be left in the beaker for several reasons. First of all, the ignition area should be contained to keep the experiment safe, and this is done by keeping the end of the tubing immersed in the layer of foam. Secondly, the amount of hydrogen you produce is enough to ignite the foam several times, so it is more convenient to leave the setup as is.

I already ignited some foam, but the hydrogen is continuing to form and more foam is appearing. Can I ignite it too?

Yes, you can ignite any new foam that appears. You can also gently swirl the flask or add more magnesium strips to repeat the experiment.

Step-by-step instructions

Prepare some soapy water.


Prepare your makeshift gas generator.


Sodium hydrogen sulfate NaHSO4 is going to react with magnesium Mg to produce some hydrogen gas. You don’t want there to be any oxygen in the flask, so add some sodium carbonate Na2CO3. It quickly reacts with NaHSO4 to produce carbon dioxide gas CO2, which fills the flask and expels any air.


Hydrogen gas is released, filling the soap bubbles.


Try to ignite the foam and see what happens. Swirl the flask or add more magnesium strips to repeat the experiment.



Please refer to local regulations when disposing of chemicals. Dispose of other solid waste with household garbage. Pour leftover solutions down the sink. Wash with an excess of water.

Scientific description

Foam is composed of bubbles. Bubbles of most of the foams you come across in everyday life are filled with carbon dioxide CO2 (such as the foam in a carbonated drink) or a mixture of gases/ordinary air (such as the foam in a bathtub). Neither air nor carbon dioxide burn. That is, the oxygen O2 in the air does not react with other components of the air, and carbon dioxide CO2 is even used in some fire extinguishers to the opposite effect. But not all gases are quite so tame. Hydrogen gas H2 loves to react with oxygen O2, and even a tiny spark can initiate this reaction. In other words, hydrogen gas burns really well.

In a sense, many chemical reactions are quarrels between different elements about who gets more electrons. In this experiment, hydrogen ions (hydrogen atoms with their only electron missing) H+  easily drag electrons  away from magnesium Mg . Newly equipped with electrons, the hydrogen atoms bond in pairs as H2  molecules, which form the gas that fills the foam bubbles .

Hydrogen isn't the greediest element of them all. The oxygen O2 in the air is extremely keen to take electrons from others, and H2 is fair game. Even a spark or a glowing splint can initiate a reaction in which oxygen O2 snatches electrons from H2. A stable compound forms, with oxygen O keeping a strong grip on the electrons from two hydrogen H atoms. Since this compound has two H and one O atom, its formula is H2O — also known as water.

Why is it so easy to ignite the hydrogen soap foam?

Hydrogen gas is extremely flammable. It forms a flammable mixture at a concentration of just 4% in the air! Due to hydrogen’s high chemical reactivity, the thermal impulse needed to ignite it is about 10 times less than that necessary to ignite an equivalent mixture of air and natural gas. A mixture of air and hydrogen, with the latter’s concentration between 6 and 67%, often ignites with an explosion. It is crucial to observe safety precautions when working with hydrogen. As soon as the impulse is given, this simple reaction starts:

2H2 + O2 → 2H2O

However, the reaction, which appears so simple at first glance, is, in fact, a much more interesting and complicated process. Let’s take a short trip into the reaction mixture under 100 000 000 magnification to see what happens during the explosion!

Follow up

What else can I do with the foam?

Try igniting the foam on your palm! Remove your protective gloves, collect some foam in your hand, and ignite it! Have fun!

That’s interesting!

Where do we use hydrogen?

Hydrogen is the first element in the periodic table. It is the lightest and most abundant element in the universe. It is almost omnipresent, in water, stars, the human body, man-made items, and much more. It combines with nitrogen to yield ammonia, which is used in the production of fertilizers, plastic materials, and explosives. Hydrogen was once used to fill airships and balloons, but its flammability, combined with the fact that mixtures of hydrogen and air are highly explosive, led to its ultimate replacement by helium. Nowadays, hydrogen is employed to obtain solid products from liquid oils, such as in the manufacture of margarine or peanut oil. It is also used to this end in the production of some cosmetics, such as soap. Moreover, it can be employed as a coolant in generators. Hydrogen peroxide is used as a cleaning and bleaching agent, and to sterilize cuts and abrasions. In addition, liquid hydrogen is a common component of rocket fuel, where it contributes to the jet acceleration needed to launch spacecraft.