Online Encyclopedia
Search over 40,000 articles from the original, classic Encyclopedia Britannica, 11th Edition.
OXIDE
Online EncyclopediaEncyclopedia Home :: ORC-PAI
del.icio.us it!
|
OXIDE , in See also:chemistry, a binary See also:compound of See also:oxygen and other elements. In See also:general, oxides are the most important compounds with which the chemist has to See also:deal, a study of their See also:composition and properties permitting a valuable See also:comparative investigation of the elements. It is possible to bring about the See also:direct See also:combination of oxygen with most of the elements (the presence of traces of See also:water vapour is generally necessary according to the researches of H. B. See also:Baker), and when this is not so, indirect methods are available, except with See also:bromine and See also:fluorine (and also with the so-called inert gases—See also:argon, See also:helium, &c.), which so far have yielded no oxides. Most of the elements combine with oxygen in several proportions, for example See also:nitrogen has five oxides: N2O, NO, N2O3, NO2, N205; for classificatory purposes, however, it is advantageous to assign a typical oxide to each See also:element, which, in general, is the highest having a basic or See also:acid See also:character. Thus in See also:Group I. of the periodic See also:system, the typical oxide is M2O, of Group II. MO, of Group III. M203, of Group IV. MO2, of Group V. M205, of Group VI. MO3. Five See also:species of oxides may be distinguished: (I) basic oxides, (2) acidic oxides, (3) neutral oxides, (4) peroxides, (5) mixed anhydrides and salts. Basic oxides combine with acids or acidic oxides to See also:form salts; similarly acidic oxides combine with basic oxides to form salts also. The former are more usually yielded by the metals (some metals, however, form oxides belonging to the other See also:groups), whilst the latter are usually associated with the non-metals. An oxide may be both acidic and basic, i.e. combine with bases as well as acids; this is the See also:case with elements occurring at the transition between basigenic and oxygenic elements in the periodic See also:classification, e.g. See also:aluminium and See also:zinc. Neutral oxides combine neither with acids nor bases to give salts nor with water to give a See also:base or acid. A typical member is nitric oxide; See also:carbon monoxide and nitrous oxide may also be put in this class, but it must be remembered that these oxides may be regarded, in some measure at least, as the anhydrides of formic and hyponitrous acid, although, at the same See also:time, it is impossible to obtain these acids by See also:simple hydration of these oxides. Peroxides may in most cases be defined as oxides containing rnore oxygen than the typical oxide. The failure of this See also:definition is seen in the case of See also:lead dioxide, which is certainly a peroxide in properties, but it is also the typical oxide of Group IV. to which lead belongs. All peroxides have oxidizing properties. Peroxides may be basic or acidic. Some basic oxides yield See also:hydrogen peroxide with acids, others yield oxygen (these also liberate See also:chlorine from hydrochloric acid), and may combine with See also:lower acidic oxides to form salts of the normal basic oxide with the higher acidic oxide. Examples are BaOz+H2SO4 = BaSO4+H2O2; 2MnO2+2H2SO4=2MnSO4+2H20+02; M nO2 +4HC1 = MnC12 + 2H20+C12i Pb02+S02=PbSO4 (i.e. PbO+S03). Two species of basic peroxides may be distinguished: (i) the superoxides or peroxidates, containing the oxygen atoms in a See also:chain, e.g. Na • O.O • Na, O • Ba.O, which yield hydrogen peroxide with acids ; and (2) the polyoxides, having the oxygen atoms doubly linked to the metallic See also:atom, e.g. 0 : Mn: O, O : Pb : O, and giving oxygen with sulphuric acid, and chlorine with hydrochloric. L. See also:Marino (Zeit. anorg. Chem., 1907, 56, p. 233) pointed out that See also:manganese and lead dioxide behaved differently with See also:sulphur dioxide, the former giving dithionate and the latter sulphate, and suggested the following formulae: O: Mn :0, O•Pbi O, as explaining this difference. A simpler explanation is that the manganese dioxide first gives a normal sulphite which rearranges to dithionate, thus: MnO2+2502= Mn(SOi)2->MnS2Os, whilst the lead dioxide gives a basic sulphite which rearranges to sulphate, thus: PbO+SO2=PbOSO3-PbSO4. Acidic peroxides combine with basic oxides to form " per " salts, and by loss of oxygen yield the acidic oxide typical of the element. Mixed anhydrides are oxides, which yield with water two acids, or are salts composed of a basic and acidic oxide of the same See also:metal. Examples of mixed anhydrides are C102 and NO2, which give chlorous and chloric acid, and nitrous and nitric acid: 2C102+ See also:H2O=HC1O2+HCIO3, 2NO2+H20=HNO2+HNO3; and of mixed salts Pb203 and Pb304, which may be regarded as lead See also:meta- and ortho-plumbate: PbO•PbO2, 2PbO•PbO2. Oxidation and Reduction.—In the narrow sense " oxidation " may be regarded as the combination of a substance with oxygen, and conversely, " reduction " as the See also:abstraction of oxygen; in the wider sense oxidation includes not merely the addition of oxygen, but also of other electro-negative elements or groups, or the removal of hydrogen or an electro-See also:positive element or group. In inorganic chemistry oxidation is associated in many cases with an increase in the active See also:valency. Ignoring processes of oxidation or reduction simply brought about by See also:heat or some other form of See also:energy, we may regard an oxidizing See also:agent as a substance having a strong See also:affinity for electro-positive atoms or groups, and a reducing agent as having a strong affinity for electro-negative atoms or groups; in the actual processes the oxidizing agent suffers reduction and the reducing agent oxidation. Many substances undergo simultaneous oxidation and reduction when treated in a particular manner; this is known as self- or auto-oxidation. For example, on boiling an aqueous See also:solution of a hypochlorite, a chlorate and a chloride results, See also:part of the See also:original See also:salt being oxidized and part reduced: 3NaOC1=NaCIO3+2NaCl. Similarly phosphorous and hypophosphorous acids give phosphoric acid and phosphine, whilst nitrous acid gives nitric acid and nitric oxide: 4H3P03=3H3PO4+PH3; 2H3P02=H3PO4+PH3; 3HNO2= HNO3+2NO+H20. In organic chemistry, a celebrated example is See also:Cannizzaro's reaction wherein an aromatic aldehyde gives an acid and an See also:alcohol: 2C6H6CHO+H2O=C6H5CO2H+C6H5CH2OH. The important oxidizing agents include: oxygen, See also:ozone, per-oxides, the See also:halogens chlorine and bromine, oxyacids such as nitric and those of chlorine, bromine and See also:iodine, and also chromic and permanganic acid. The important reducing agents include hydrogen, hydrides such as those of iodine, sulphur, See also:phosphorus, &c., carbon, many metals, See also:potassium, See also:sodium, aluminium, See also:magnesium, &c., salts of lower oxyacids, lower salts of metals and lower oxides. Additional information and CommentsThere are no comments yet for this article.
» Add information or comments to this article.
Please link directly to this article:
Highlight the code below, right click, and select "copy." Then paste it into your website, email, or other HTML. Site content, images, and layout Copyright © 2006 - Net Industries, worldwide. |
|
|
[back] OXFORDSHIRE (or OxoN) |
[next] OXIMES |