Кислород

Описание

Oxygen is a very prevalent and important element and is necessary for sustaining life on this planet. This element is the third most abundant in mass behind helium and hydrogen in the universe. The diatomic form (O2) is the most common pure form. With a boiling point at -183 °C, O2 exists as a colorless and odorless gas at standard temperature and pressure. In the process of cellular respiration, the highly reactive O2 is used as the oxidant in breaking down food molecules to produce energy. In turn, photosynthetic organisms generate O2 by using energy from the sun and water. Other allotropes of pure oxygen exist, including the trioxygen (O3) form known as ozone, as well as other, less common allotropes of oxygen such as O4 and O8. These oxygen allotropes are formed under high pressure and low temperatures and are solid.

Химические свойства

Oxygen, O2, is a colorless, tasteless, gaseous element essential to almost all forms of life. It promotes respiration and combustion. Oxygen comprises 20% of the earth's atmosphere and is the most abundant element in seawater and in the earth's crust. It is slightly soluble in water and alcohol, but combines readily with most other elements to form oxides. The electrolysis of water produces both oxygen and hydrogen.

Физические свойства

There are three allotropes (different forms) of oxygen: (1) atomic oxygen (O), sometimesreferred to as nascent or “newborn” oxygen; (2) diatomic oxygen (O₂), or molecular oxygen(gas); and (3) ozone (O₃), also a gas.
The atmospheric oxygen that we breathe is a very reactive nonmetal and is colorless, odorless,and tasteless, but it is essential to all living organisms. It readily forms compounds withmost other elements. With six electrons in its outer valence shell, it easily gains two moreelectrons to form a negative (–2) ion; or as covalent, it can share electrons with other elementsto complete its outer shell.
Almost all the oxygen in the atmosphere (?21%) is the allotropic form of molecular oxygen(O₂). This essential gas we breathe is the result of photosynthesis, which is how green plants(with chlorophyll) use the energy of the sun to convert carbon dioxide (CO₂) and water tostarches and sugars with molecular oxygen as the by-product.
Liquid oxygen has a slightly bluish cast to it. As it boils, pure oxygen gas is released. Themelting point for oxygen is –218.79°C, its boiling point is –182.95°C, and its density is0.001429 g/cm³.

Изотопы

There are a total of 15 isotopes of oxygen, three of which are stable. The stableones are O-16, which accounts for 99.762% of all the oxygen on Earth; O-17, whichcontributes only 0.038% of the Earth’s oxygen; and O-18, which makes up just 0.200%of Earth’s oxygen.

Характеристики

Oxygen is, without a doubt, the most essential element on Earth. It is required to supportall plant and animal life, and it forms more compounds with other elements than any otherelement.
Oxygen is soluble in both water and alcohol. Contrary to what many people believe, oxygenis NOT combustible (it will not burn), but rather it actively supports the combustion ofmany other substances. After all, if oxygen burned, every time a fire was lit, all the O₂ in theatmosphere would be consumed!
Burning is a form of oxidation wherein oxygen chemically combines with a substance rapidlyenough to produce adequate heat to cause fire and light, or to maintain a fire once started.The oxidation of iron is called rusting. Rusting in an example of “slow oxidation,” which isthe reaction of O₂ with Fe to form Fe₂O₃ or Fe₃O₄. This chemical reaction is so slow that theheat it produces is dissipated; thus, there is no fire.
Recently a new allotrope of oxygen was discovered. When O₂ is subjected to great pressure,it is converted intoO₄, which is a deep red solid that is a much more powerful oxidizer thanthe other forms of oxygen.

Использование

Oxygen has many uses due to its high electronegativity with the ability to oxidize manyother substances. Only fluorine has higher electronegativity and is thus a stronger oxidizer.Besides the essential use to support life, oxygen has many other uses.
It is used in the smelting process to free metals from their ores. It is particularly importantin the oxygen-converter process in the production of steel from iron ore.
Oxygen is used in making several important synthetic gases and in the production ofammonia, methyl alcohol, and so on.
It is the oxidizer for liquid rocket fuels, and as a gas, oxygen is used in a mixture withhelium to support the breathing of astronauts and divers and to aid patients who have difficultybreathing. It is use to treat (oxidize) sewage and industrial organic wastes.
Oxygen has many uses because of its ability to accept electrons from other elements to formionic bonds or to share electrons with other elements to form covalent bonds.

Методы производства

Oxygen is the most prevalent element in the Earth’s crust, making up 49.2% by weight. It accounts for 20.95% by volume of the Earth’s atmosphere and approximately 65% by weight of the human body.

Определение

Dioxygen: the normal form of molecularoxygen, O₂, used to distinguishit from oxygen atoms or fromozone （O₃）.

Общее описание

Oxygen is a colorless, odorless and tasteless gas. Oxygen will support life. Oxygen is noncombustible, but will actively support the burning of combustible materials. Some materials that will not burn in air will burn in Oxygen. Materials that burn in air will burn more vigorously in Oxygen. As a non-liquid gas Oxygen is shipped at pressures of 2000 psig or above. Pure Oxygen is nonflammable. Under prolonged exposure to fire or intense heat the containers may rupture violently and rocket. Oxygen is used in the production of synthesis gas from coal, for resuscitation and as an inhalant.

Профиль реактивности

Propellant; ignites upon contact with alcohols, alkali metals, amines, ammonia, beryllium alkyls, boranes, dicyanogen, hydrazines, hydrocarbons, hydrogen, nitroalkanes, powdered metals, silanes, or thiols [Bretherick 1979. p.174]. Heat of water will vigorously vaporize liquid Oxygen, pressures may build to dangerous levels if this occurs in a closed container. Liquid Oxygen gives a detonable mixture when combined with powdered aluminum [NFPA 491M. 1991].

Опасность

Although oxygen itself is not flammable or explosive, as is sometimes believed, its mainhazard is that, in high concentrations, oxygen can cause other materials to burn much morerapidly.
Oxygen is toxic and deadly to breathe when in a pure state at elevated pressures. In addition,such pure oxygen promotes rapid combustion and can produce devastating fires, such asthe fire that killed the Apollo 1 crew on a test launch pad in 1967. It spread rapidly because thepure oxygen was at normal pressure rather than the one-third pressure used during flight.
Oxygen used for therapeutic purposes in adults can cause convulsions if the concentrationis too high. At one time, high levels of oxygen were given to premature infants to assist theirbreathing. It was soon discovered that a high concentration of O2 caused blindness in some ofthe infants. This practice has been abandoned, or the oxygen levels have since been reduced,and this is no longer a medical problem.
Oxygen involved in metabolic processes are prone to form “free radicals,” which arethought to cause damage to cells and possibly be associated with cancer and aging.

Угроза здоровью

Inhalation of 100% Oxygen can cause nausea, dizziness, irritation of lungs, pulmonary edema, pneumonia, and collapse. Liquid may cause frostbite of eyes and skin.

Пожароопасность

Behavior in Fire: Increases intensity of any fire. Mixtures of liquid Oxygen and any fuel are highly explosive.

Воспламеняемость и взрывоопасность

Oxygen itself is nonflammable, but at concentrations greater than 25% supports and vigorously accelerates the combustion of flammable materials. Some materials (including metals) that are noncombustible in air will burn in the presence of oxygen.

Сельскохозяйственное использование

Oxygen (O) is an odorless, colorless, gaseous element that belongs to group 16 (formerly group VI) of the Periodic Table. It is the most abundant element in the earth's crust (49.2% by weight), is present in the atmosphere (20% by volume) and is a constituent of water. It exists in three isotopes 16, 17 and 18. Oxygen is essential for respiration of most living organisms and for combustion. It is used in metallurgical processes, in high temperature flames (welding) and in medical treatment.
The common form of oxygen is di-atomic oxygen (O₂) There is also another form - reactive allotrope ozone (O₃)C.h emically, oxygen reacts with most other elements forming oxides. For industrial use, it is obtained by fractional distillation of liquid air. This has been replaced by a process which utilizes ambient temperature separation by means of a pressure cycle in which molecular sieves of synthetic zeolite preferentially absorb nitrogen from air, giving 95 % oxygen and 5 % argon.
The most popular industrial use of oxygen is in oxygen enrichment of steel blast furnaces. Large quantities of oxygen are used in the synthesis of nitric acid from ammonia, methanol and ethylene oxide, as also in oxy-acetylene welding.

Возможный контакт

Compressed oxygen is used in various oxidation processes, for feedstock; and enrichment purposes; as a medicinal gas; a chemical intermediate; in oxyacetylene welding; in metallurgy. Liquid oxygen is used as a rocket fuel. Oxygen is naturally present at a concentration of 21% in breathing air.

Канцерогенность

Exposure to ionizing radiation is recognized as a cause of cancer, and the production of free radicals in the exposed cells is a part of the process. If hyperoxia causes free radical formation, it may contribute to the occurrence of cancer. Although a direct relation of hyperoxic injury and cancer has not been proven, numerous instances of association in experimental animals exist. Reactive oxidative intermediates have been shown to cause chromosome breaks and damage to DNA that can initiate carcinogenesis. Experimental work done with mouse skin tumors (as models of human tumors) has been both revealing and confusing. A substance may act as a cancer initiator or as a promoter, or sometimes both, depending on intensity and duration of exposure, and the presence of other carcinogenic materials. The same substance can also inhibit cancer growth. Hyperoxia has clearly been involved in modifying the course of tumor development, but the effects have differed under varying circumstances.

Экологическая судьба

Atmospheric air contains 20.8% O2. Despite consumption of O2 through respiration and oxidative processes, this concentration remains constant, most likely due to the depleted O2 being replaced by plant-generated O2 in the photosynthetic process. O2 does not bioaccumulate in organisms as pure oxygen.

Перевозки

UN1072 Oxygen, compressed & UN1073 Oxygen, refrigerated liquid (cryogenic liquid), Hazard Class: 2.2; Labels: 2.2-Nonflammable compressed gas; 5.1- Oxidizer. Cylinders must be transported in a secure upright position, in a well-ventilated truck. Protect cylinder and labels from physical damage. The owner of the compressed gas cylinder is the only entity allowed by federal law (49CFR) to transport and refill them. It is a violation of transportation regulations to refill compressed gas cylinders without the express written permission of the owner.

Методы очистки

Purify it by passing the gas over finely divided platinum at 673oK and Cu(II) oxide (see under nitrogen) at 973o, then condensed in a liquid N2-cooled trap. HIGHLY EXPLOSIVE in contact with organic matter.

Несовместимости

A strong oxidizer. Reacts violently with nearly every element, combustibles, organics, and reducing materials.

Утилизация отходов

Return refillable compressed gas cylinders to supplier. Vent to atmosphere.