Discovery of oxygen 1774 British chemist J. priestley focused sunlight with a large convex lens, and then heated mercury oxide to produce pure oxygen. It was found that pure oxygen supported combustion and helped breathing, which was called "dephosphorized air". Sweden's C.W. Scheler made oxygen by heating mercuric oxide and other oxyacid salts one year earlier than priestley, but his paper "Chemistry on Air and Fire" was not published until 1777, but they did make oxygen independently. 1774, priestley visited France and told A.-L. lavoisier how to make oxygen. The latter repeated the experiment in 1775 and called the gas in the air oxygen, which comes from the Greek word oxygen and means "acid producer". So these three scholars are all recognized oxygen discoverers in later generations.
There are three stable isotopes of oxygen, namely oxygen 16, oxygen 17 and oxygen 18, among which the content of oxygen 16 accounts for 99.759%. The content of oxygen in the crust is 48.6%, ranking first. Oxygen is widely distributed on the earth, accounting for 265,438+0% in the atmosphere, and oxygen compound water is everywhere in oceans, rivers and lakes, accounting for 88.8% in water. There are many oxygenated salts on the earth, such as aluminosilicate contained in soil, and minerals such as silicate, oxide and carbonate. Oxygen in the atmosphere is constantly used for animal metabolism, and oxygen in human body accounts for 65%. Photosynthesis of plants can convert carbon dioxide into oxygen, which keeps the oxygen circulating. Although the earth is full of oxygen, it is mainly extracted from the air and there are inexhaustible resources.
Physical and physical properties: Oxygen is a colorless, odorless and tasteless gas with a melting point of -2 18.4℃, a boiling point of-182.962℃, a gas density of 1.429 g/cm3, and liquid oxygen is light blue.
Oxygen is a chemically active element. Except chlorine, bromine, iodine and some inert metals (such as gold and platinum) in inert gases and halogens, most nonmetals and gold metals can be directly combined with oxidation, but oxygen can react with the inert gas xenon to generate oxides through indirect methods:
XeF6 + 3H2O=XeO3 + 6HF
Similarly, chlorine oxide can also be prepared by indirect methods:
2Cl2+2HgO=HgO？ Mercury chloride+chlorite oxide
At room temperature, oxygen can also oxidize other compounds:
2NO+O2=2NO2
Oxygen can oxidize glucose, which is the main reaction that constitutes organism respiration:
C6H 12O6+6O2=6CO2+6H2O
The oxidation states of oxygen are -2,-1 and +2. The oxidation of oxygen is second only to that of fluorine, so when oxygen reacts with fluorine, it appears with a valence of +2, forming oxyfluoride (F2O). The binary compounds formed by oxygen and metal elements are oxides, peroxides and superoxides. Oxygen molecules can lose an electron, generating molecular oxygen (), forming compounds such as O2PtF6.
The laboratory preparation methods of oxygen are as follows: ① thermal decomposition of potassium chlorate:
(2) Electrolytic water:
③ Thermal decomposition of oxides:
(4) using manganese dioxide as a catalyst to decompose hydrogen peroxide;
⑤ Thermal decomposition of potassium permanganate
In the spacecraft, the carbon dioxide gas exhaled by astronauts can react with potassium peroxide to produce oxygen for astronauts to breathe.
The method of large-scale production and application of oxygen is fractionation of liquid air. First compress the air, then freeze it into liquid air. Because the boiling points of rare gases and nitrogen are lower than that of oxygen, the remaining liquid oxygen after fractionation can be stored in high-pressure steel cylinders. All oxidation reactions and combustion processes need oxygen, such as removing impurities such as sulfur and phosphorus during steelmaking. When the mixture of oxygen and acetylene burns, the temperature is as high as 3500℃, which is used for welding and cutting steel. Oxygen is needed for glass manufacturing, cement production, mineral roasting and hydrocarbon processing. Liquid oxygen is also used as rocket fuel, which is cheaper than other fuels. People who work in anoxic or anoxic environment, such as divers and astronauts, oxygen is indispensable to maintain life. However, the active state of oxygen, such as OH and H2O2, has serious damage to biological tissues, and the damage of ultraviolet rays to skin and eyes is mostly related to this effect. It is one of the components of air, colorless, odorless and tasteless. The density of oxygen is higher than that of air, and it is 10 1325pa under standard conditions (0℃, atmospheric pressure) .429g/l. It is soluble in water, but the solubility is very small. About 30mL of oxygen can be dissolved in 1L water. When the pressure is 10 1kPa, oxygen turns into a light blue liquid at about-180℃ and turns into a snowy light blue solid at about -2 18℃.
1. Oxygen can directly combine with many elements to form oxides.
2. Oxygen is a necessary gas for animals and plants to burn and breathe. Oxygen-enriched air is used for medical treatment and high-altitude flight, pure oxygen is used for steelmaking, cutting and welding metals, and liquid oxygen is used as oxidant for rocket engines.
3. Oxygen used in production is fractionated from liquid air. Oxygen is produced by the decomposition of oxygen-containing salts (potassium chlorate, potassium permanganate, etc.). ) by heating in the laboratory.
4. An oxygen molecule consists of two oxygen atoms with an atomic radius of 0.074 nm.
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