How to Make Liquid Oxygen or Liquid O2

Liquid oxygen or O₂ is an interesting blue liquid that you can prepare quite easily yourself. There are several ways to make liquid oxygen. This one uses liquid nitrogen to cool oxygen from a gas into a liquid.

Liquid Oxygen Materials

• A cylinder of oxygen gas
• 1-liter Dewark of liquid nitrogen
• Test tube (approximately 200ml)
• Rubber tubing
• Glass tubing (to fit inside test tube)

Preparation

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1. Clamp a 200-ml test tube so that it will sit in a bath of liquid nitrogen.
2. Connect one end of a length of rubber tubing to an oxygen cylinder and the other end to a piece of glass tubing.
3. Place the glass tubing in the test tube.
4. Crack open the valve on the oxygen cylinder and adjust the flow rate of the gas so that there is a slow and gentle flow of gas into the test tube. As long as the flow rate is slow enough, liquid oxygen will begin to condense in the test tube. It takes approximately 5-10 minutes to collect 50 mL of liquid oxygen.
5. When you have collected sufficient liquid oxygen, close the valve on the oxygen gas cylinder.

Liquid Oxygen Uses

You can use liquid oxygen for many of the same projects you would perform using liquid nitrogen. It's also used to enrich fuel, as a disinfectant (for its oxidizing properties), and as a liquid propellant for rockets. Many modern rockets and spacecraft use liquid oxygen engines.

Safety Information

• Oxygen is an oxidizer. It reacts very readily with combustible materials. According to the Canadian Centre for Occupational Health and Safety (CCOHS), materials you may ordinarily consider non-combustible, such as steel, iron, Teflon, and aluminum, may burn with liquid oxygen. Flammable organic materials may react explosively. It's important to work with liquid oxygen away from a flame, spark, or heat source.
• Liquid nitrogen and liquid oxygen are extremely cold. These materials are capable of causing severe frostbite. Avoid skin contact with these liquids. Also, take care to avoid touching any object which has been in contact with the cold fluids, since it may also be very cold.
• Dewars are easily broken by mechanical shock or exposure to extreme temperature changes. Take care to avoid striking the Dewar. Don't slam a cold Dewar on a warm countertop, for example.
• Liquid oxygen boils off to form oxygen gas, which enriches the concentration of oxygen in the air. Use care to avoid oxygen intoxication. Work with liquid oxygen outdoors or in well-ventilated rooms.

Disposal

If you have leftover liquid oxygen, the safest way to dispose of it is to pour it over a noncombustible surface and allow it to evaporate into the air.

Interesting Liquid Oxygen Fact

Although Michael Faraday liquefied most gases known at the time (1845), he was unable to liquefy oxygen, hydrogen, nitrogen, methane, carbon monoxide, and methane. The first measurable sample of liquid oxygen was produced in 1883 by Polish professors Zygmunt Wróblewski and Karol Olszewski. A couple of weeks later, the pair successfully condensed liquid nitrogen.