Oxygen

(a simple substance formed by oxygen)

Oxygen gas is an elemental substance formed by oxygen, with the chemical formula O2. Its chemical properties are relatively active, and it can react with most elements. It is not very active at room temperature, and it is not easy to interact with many substances. However, it is very active at high temperature and can directly combine with various elements, which is related to the electronegativity of oxygen atom, which is second only to fluorine.

Oxygen is a colorless, odorless gas and the most common elemental form of oxygen. Melting point -218.4 ℃, boiling point -183 ℃. Not easily soluble in water, about 30mL of oxygen is dissolved in 1L of water. Oxygen is about 21% in the air. Liquid oxygen is sky blue. Solid oxygen is a blue crystal.

Oxygen is the most widely distributed in nature, accounting for 48.6% of the mass of the earth's crust, and is the most abundant element. Oxygen is needed in the oxidation of hydrocarbons, the treatment of wastewater, rocket propellants, and the breathing of animals and humans in aviation, spaceflight, and diving. Oxygen is consumed by animal respiration, combustion, and all oxidative processes, including the putrefaction of organic compounds. But the oxygen in the air can be continuously replenished through the photosynthesis of plants. In the cutting and welding of metals, it uses oxygen with a purity of 93.5%~99.2% mixed with combustible gas (such as acetylene) to generate a very high temperature flame to melt the metal. Metallurgical processes are inseparable from oxygen. Oxygen is also required to intensify the production process of nitric acid and sulfuric acid. The gas with high calorific value can be obtained by blowing the mixture of oxygen and water vapor into the gasifier without air.  Medical gas is extremely important.