Oxygen is an element of the chalcogen group–group VI on the periodic table–and occurs most frequently in elemental form as the diatomic molecule O2. At standard atmospheric pressure and normal temperature, elemental oxygen is a gas–its boiling point is -182.95 degrees Celsius at 1 atm, according to the CRC Handbook of Chemistry and Physics. At high pressures or very low temperatures, however, it is possible to liquefy oxygen, which has primary utility as a cryogenic liquid.
Chemical Characteristics
Molecules of liquid oxygen are composed of two atoms of the element oxygen, and have a molar mass of 32 grams/mol. The molecule is characterized by a non-polarized double bond, or two shared pairs of electrons, meaning that liquid oxygen and the vapor released from liquid oxygen spills have no global warming or ozone-depleting potential.
Physical Properties
According to the Material Safety Data Sheet (MSDS) for liquid oxygen, it is a light blue liquid with no apparent odor, and a freezing point of -218.8 degrees Celsius. Its water solubility is slight, due mostly to the fact that the oxygen molecule is non-polar, making it a poor solute in highly polar solvents, such as water. It has a specific gravity of 0.967 at 21 degrees Celsius, meaning that it is 96.7 percent as dense as, or slightly less dense than, water.
Chemical Properties
Liquid oxygen is nontoxic, and direct contact does not result in chemical reaction with or on the surface of the skin. The MSDS indicates that while it is stable, oxygen is highly combustible and represents a fire hazard. It is not subject to polymerization, nor does it decompose into hazardous products of any kind.
Biological Characteristics
If spilled, liquid oxygen quickly vaporizes into gaseous form. Many of the risks associated with liquid oxygen exposure, as indicated on the MSDS, are more closely associated with its temperature than its chemical nature. Frostbite, in particular, is a concern. Contact with the vapor released from liquid oxygen is not a problem topically, but inhalation of high concentrations of vaporized oxygen from liquid spills can result in depression of the central nervous system, respiratory symptoms and potential damage to the lungs.
