Most people understand that oxygen is a gas under "normal" conditions. But, what happens if we cool oxygen gas down to the point that it is no longer a gas and it becomes a liquid? The properties of oxygen and how it acts change drastically when it changes phases from a gas to a liquid. I set out to explore the interesting properties of liquid oxygen by experimenting in the chemistry lab.
What is liquid oxygen?
First, we should probably understand oxygen gas before we go any further. Oxygen is an element that has 8 protons and exists as a gas a standard atmospheric temperature and pressure (SATP). Oxygen makes up about 21% of the air we breathe (at sea level). If oxygen is cooled below -183 deg C (-297.3 deg F) the fast moving gas molecules start to slow down and begin to "stick" to each other and it behaves as a liquid. If the liquid oxygen begins to warm up to a temperature above its boiling point (-183 deg C or -297.3 deg F) it will turn back into a gas.
How to Make Liquid Oxygen using Liquid Nitrogen
There are several ways to make liquid oxygen but the easiest way I've found to make liquid oxygen is by using liquid nitrogen to cool it to the condensation point. Liquid nitrogen is -196 degrees C (-320 degrees F) so it is cold enough to cool oxygen gas below it's condensation temperature (the point where it turns to a liquid). Why do I use liquid nitrogen? Liquid oxygen is not readily available but, in most areas, liquid nitrogen is available from welding supply companies or medical suppliers.
Supplies
Liquid Nitrogen Dewar Flask (for transporting liquid nitrogen)
Insulated container without a lid* (I use a drink container like this*)
*Do not place liquid nitrogen into a container with a sealed lid. As the nitrogen turns to gas it will explode! The specialized Liquid Nitrogen Dewar Flask has a non-sealable lid to allow pressure to escape.
Procedure
Fill a balloon with oxygen gas and place the opening of a large test tube over the opening of the balloon. Fill an insulated container with liquid nitrogen and place the glass test tube (with the balloon on top) into the liquid nitrogen. The gas will cool and condense into a liquid in the test tube. The balloon will continue to shrink as gas turns to liquid. Remove the test tube that is now filled with liquid oxygen.
Safety Concerns
This should only be performed by a qualified teaching professional. Liquid nitrogen and liquid oxygen will freeze skin and eyes, take precautions.
Liquid Oxygen Experiments
Burning Food with Liquid Oxygen Demonstration
Supplies
Dry Snack Food (ex. chip, peanut, cracker)
Beaker or non-flammable container
Procedure
Place a piece of dry snack food in a non-flammable container. Light the food on fire and carefully pour the liquid oxygen over the fire.
Safety Concerns
This should only be performed by a qualified teaching professional. Beware of the flames. Liquid nitrogen and liquid oxygen will freeze skin and eyes, take precautions. Avoid staring into the flame when adding liquid oxygen, the bright light may damage your eyes. This demonstration will produce a lot of smoke (see image) - take precautions.
Liquid Oxygen Paramagnetism Demonstration
Supplies
Procedure
Experiment with the magnetic properties of liquid oxygen in any way you wish.
Safety Concerns
This should only be performed by a qualified teaching professional. Liquid nitrogen and liquid oxygen will freeze skin and eyes, take precautions.
Making Steel Wool Rust with Liquid Nitrogen Demonstration
Supplies
Procedure
Pour liquid oxygen into a beaker. Light a small piece of steel wool and drop it into the beaker. As the liquid oxygen turns to a gas, it will allow the rate of the combustion reaction to speed up. This demonstration models how rust forms as iron reacts with oxygen.
Safety Concerns
This should only be performed by a qualified teaching professional. Beware of the flames. Liquid nitrogen and liquid oxygen will freeze skin and eyes, take precautions.
If you have other ideas for experiments with liquid oxygen, feel free to contact me and I will add them to the list.
Keep on Learning! ~Craig Beals