A characteristic property of oxygen is the ability to react compounds with many elements. The oxidation reaction proceeds with the release of heat, and sometimes accompanied by the release of light and even an explosion. The chemical compounds resulting from this reaction are called oxides. Some elements form only one oxide with oxygen, while others form several oxides of various compositions.
According to the state of aggregation, oxides are solid, liquid, and gaseous ; most oxides are solids. Oxides of alkaline, alkaline earth, and also some other metals and nonmetals are crystalline white substances.
Many oxides are colored in various colors: from light yellow (niobium pentoxide, antimony pentoxide, sodium peroxide, etc.) to black [iron oxide (II), tin oxide, etc.].
The vast majority of oxides has the ability to directly or indirectly interact with water. Five main groups of oxides are distinguished depending on the ratio of oxides to water and on the properties of the resulting compounds: acidic, basic, amphoteric, indifferent, and peroxides.
Acid oxides or acid anhydrides are oxides that form acids with water. This group includes non-metal oxides (sulfuric anhydride SO3, sulfuric anhydride SO2, phosphoric anhydride or phosphorus pentoxide P2O5, carbon dioxide CO2, nitric anhydride N2O5, etc.), as well as higher oxides of some metals (chromic anhydride CrO3, manganese anhydride and others Mg2 .).
Basic oxides are oxides that form bases with water. Basic oxides are formed only from metals (Na2O, MgO BaO, HgO), non-metals do not produce basic oxides.
Amphoteric oxides . Some metals form oxides, which simultaneously have the properties of acidic and basic oxides. Such oxides are called amphoteric. These include beryllium oxides BeO, zinc ZnO, aluminum Al2O3, chromium Cr2O3, tin SnO, lead PbO, etc. Amphoteric oxides practically do not react with water.
Elements of even rows of large periods of groups IV – VIII of the periodic system of elements of D. I. Mendeleev are capable of forming several oxides — basic, amphoteric, and acid .
For example, manganese, located in the fourth period, fourth row and seventh group, forms five oxides: manganese oxide MgO, manganese oxide Mg2O3, manganese dioxide MgO2, manganese anhydride MgO3 (it is not isolated in its free form) and manganese anhydride Mg2O7.
Of these, the first two are basic, the third is amphoteric, and the last two are acidic in nature.
Indifferent oxides. Basic, acidic and amphoteric oxides are capable of forming salts, which is why they are called salt-forming oxides. There are a small number of oxides that do not interact with either acids or bases. These oxides are called indifferent or indifferent. These include carbon monoxide CO, nitrous oxide N2O, nitric oxide NO. They do not form salts.
Peroxides are oxides that contain more oxygen than ordinary oxides of these elements. A distinctive feature of peroxides is that the oxygen atoms in the peroxide molecule are bonded not only to the atoms of another element, as in ordinary oxides, but also to each other, forming the so-called peroxide (peroxide) chain.
Some elements also form dioxide, for example carbon dioxide СО2, manganese dioxide MgO2, nitrogen dioxide NO2, but this is not peroxide, since there is no peroxide chain in their molecule.
Hydrogen peroxide and other peroxides are only formally classified as oxides, since hydrogen peroxide is a weak dibasic acid, and metal peroxides are salts of this acid. Metal peroxides are strong oxidizing agents, and hydrogen peroxide in some cases exhibits the properties of a reducing agent.
Application. Oxides are widely used in inorganic synthesis as a feedstock for the production of bases, acids, salts and other compounds, as well as catalysts for chemical processes (beryllium oxide, vanadium pentoxide, osmium tetroxide, etc.).
Many metal oxides of reactive purity or special additional purification are used as technological raw materials in new branches of technology. For example, calcium oxide, beryllium oxide, silicon dioxide - in the production of phosphors; iron oxide, nickel oxide - to obtain ferrite materials; manganese oxide, silicon dioxide - for semiconductor technology; copper oxide - for radio electronics, etc.
Many oxides are used in analytical practice. Thus, alumina serves as a sorbent for the absorption of bode vapor and certain gases, as well as a carrier in gas-liquid chromatography for the separation of mixtures of organic substances. Magnesium oxide as an integral part of the Eshka mixture is used to determine sulfur in coals; it also serves as a white standard; copper oxide — in organic elemental analysis and in the performance of qualitative reactions to halogens in organic substances; arsenic anhydride - in a titrimetric analysis to establish the titer of solutions, as well as as a chlorine absorber; boric anhydride and lead oxide - as fluxes for the decomposition of silicates, etc.
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