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词条 Oxyacid
释义

  1. Description

  2. Properties

  3. Names of inorganic oxyacids

      Examples  

  4. Sources

  5. See also

  6. References

  7. External links

{{refimprove|date=March 2016}}{{distinguish|text=keto acids, also known as oxocarboxylic acids, which are a type of oxoacid}}

An oxyacid, or oxoacid, is an acid that contains oxygen. Specifically, it is a compound that contains hydrogen, oxygen, and at least one other element, with at least one hydrogen

Description

Under Lavoisier's original theory, all acids contained oxygen, which was named from the Greek ὀξύς (oxys: acid, sharp) and the root -γενής (-genes: creator). It was later discovered that some acids, notably hydrochloric acid, did not contain oxygen and so acids were divided into oxyacids and these new hydroacids.

All oxyacids have the acidic hydrogen bound to an oxygen atom, so bond strength (length) is not a factor, as it is with binary nonmetal hydrides. Rather, the electronegativity of the central atom (X) and the number of O atoms determine oxyacid acidity. With the same central atom X, acid strength increases as the number of oxygens attached to X increases. With the same number of oxygens around E, acid strength increases with the electronegativity of X.

Compared to salt of their deprotonated forms, the oxyanions, oxyacids are generally less stable, and many of them only exist formally as hypothetical species, or exist only in solution and cannot be isolated in pure form. There are several general reasons for this: (1) they may condense to form oligomers (e.g., H2CrO4 to H2Cr2O7), or dehydrate all the way to form the anhydride (e.g., H2CO3 to CO2), (2) they may disproportionate to one compound of higher and another of lower oxidation state (e.g., HClO2 to HClO and HClO3), or (3) they might exist almost entirely as another, more stable tautomeric form (e.g., phosphorous acid P(OH)3 exists almost entirely as phosphonic acid HP(=O)(OH)2). Nevertheless, perchloric acid (HClO4), sulfuric acid (H2SO4), and nitric acid (HNO3) are a few common oxyacids that are relatively easily prepared as pure substances.

Imidic acids are created by replacing =O with =NR in an oxyacid.[1]

Properties

An oxyacid molecule contains the structure X−O−H, where other atoms or atom groups can be connected to the central atom X. In a solution, such a molecule can be dissociated into ions in two distinct ways:

  • X−O−H ⇄ (X−O)− + H+
  • X−O−H ⇄ X+ + OH−[2]

If the central atom X is strongly electronegative, then it strongly attracts the electrons of the oxygen atom. In that case, the bond between the oxygen and hydrogen atom is weak, and the compound ionizes easily in the way of the former of the two chemical equations above. In this case, the compound XOH is an acid, because it releases a proton, that is, a hydrogen ion. For example, nitrogen, sulfur and chlorine are strongly electronegative elements, and therefore nitric acid, sulfuric acid, and perchloric acid, are strong acids.

If, however, the electronegativity of X is low, then the compound is dissociated to ions according to the latter chemical equation, and XOH is an alkaline hydroxide. Examples of such compounds are sodium hydroxide NaOH and calcium hydroxide Ca(OH)2.[2] Owing to the high electronegativity of oxygen, however, most of the common oxobases, such as sodium hydroxide, while strongly basic in water, are only moderately basic in comparison to other bases. For example, the pKa of the conjugate acid of sodium hydroxide, water, is 15.7, while that of sodium amide, ammonia, is closer to 40, making sodium hydroxide a much weaker base than sodium amide.[2]

If the electronegativity of X is somewhere in between, the compound can be amphoteric, and in that case it can dissociate to ions in both ways, in the former case when reacting with bases, and in the latter case when reacting with acids. Examples of this include aliphatic alcohols, such as ethanol. [2]

Inorganic oxyacids typically have a chemical formula of type HmXOn, where X is an atom functioning as a central atom, whereas parameters m and n depend on the oxidation state of the element X. In most cases, the element X is a nonmetal, but some metals, for example chromium and manganese, can form oxyacids when occurring at their highest oxidation states.[2]

When oxyacids are heated, many of them dissociate to water and the anhydride of the acid. In most cases, such anhydrides are oxides of nonmetals. For example, carbon dioxide, CO2, is the anhydride of carbonic acid, H2CO3, and sulfur trioxide, SO3, is the anhydride of sulfuric acid, H2SO4. These anhydrides react quickly with water and form those oxyacids again.[3]

Many organic acids, like carboxylic acids and phenols, are oxyacids.[2] Their molecular structure, however, is much more complicated than that of inorganic oxyacids.

Most of the commonly encountered acids are oxyacids.[2] Indeed, in the 18th century, Lavoisier assumed that all acids contain oxygen and that oxygen causes their acidity. Because of this, he gave to this element its name, oxygenium, derived from Greek and meaning acid-maker, which is still, in a more or less modified form, used in most languages.[4] Later, however, Humphry Davy showed that the so-called muriatic acid did not contain oxygen, despite its being a strong acid; instead, it is a solution of hydrogen chloride, HCl.[5] Such acids which do not contain oxygen are nowadays known as hydroacids.

Names of inorganic oxyacids

Many inorganic oxyacids are traditionally called with names ending with the word acid and which also contain, in a somewhat modified form, the name of the element they contain in addition to hydrogen and oxygen. Well-known examples of such acids are sulfuric acid, nitric acid and phosphoric acid.

This practice is fully well-established, and IUPAC has accepted such names. In light of the current chemical nomenclature, this practice is, however, very exceptional, because systematic names of all other compounds are formed only according to what elements they contain and what is their molecular structure, not according to what other properties (for example, acidity) they have.[6]

IUPAC, however, recommends against calling future compounds not yet discovered with a name ending with the word acid.[6] Indeed, acids can be called with names formed by adding the word hydrogen in front of the corresponding anion; for example, sulfuric acid could just as well be called hydrogen sulfate (or dihydrogen sulfate).[7] In fact, the fully systematic name of sulfuric acid, according to IUPAC's rules, would be dihydroxidodioxidosulfur and that of the sulfate ion, tetraoxidosulfate(2−),[8] Such names, however, are almost never used.

However, the same element can form more than one acid when compounded with hydrogen and oxygen. In such cases, the English practice to distinguish such acids is to use the suffix -ic in the name of the element in the name of the acid containing more oxygen atoms, and the suffix -ous in the name of the element in the name of the acid containing fewer oxygen atoms. Thus, for example, sulfuric acid is H2SO4, and sulfurous acid, H2SO3. Analogously, nitric acid is HNO3, and nitrous acid, HNO2. If there are more than two oxyacids having the same element as the central atom, then, in some cases, acids are distinguished by adding the prefix per- or hypo- to their names. The prefix per-, however, is used only when the central atom is a halogen or a group 7 element.[7] For example, chlorine has the four following oxyacids:

  • hypochlorous acid HClO
  • chlorous acid HClO2
  • chloric acid HClO3
  • perchloric acid HClO4

The suffix -ite occurs in names of anions and salts derived from acids whose names end to the suffix -ous. On the other hand, the suffix -ate occurs in names of anions and salts derived from acids whose names end to the suffix -ic. Prefixes hypo- and per- occur in the name of anions and salts; for example the ion {{chem|ClO|4|−}} is called perchlorate.[7]

In a few cases, the prefixes ortho- and para- occur in names of some oxyacids and their derivative anions. In such cases, the para- acid is what can be thought as remaining of the ortho- acid if a water molecule is separated from the ortho- acid molecule. For example, phosphoric acid, H3PO4, has sometimes been called orthophosphoric acid, in order to distinguish it from metaphosphoric acid, HPO3.[7] However, according to IUPAC's current rules, the prefix ortho- should only be used in names of orthotelluric acid and orthoperiodic acid, and their corresponding anions and salts.[9]

Examples

In the following table, the formula and the name of the anion refer to what remains of the acid when it loses all its hydrogen atoms as protons. Many of these acids, however, are polyprotic, and in such cases, there also exists one or more intermediate anions. In name of such anions, the prefix hydrogen- (in older nomenclature bi-) is added, with numeral prefixes if needed. For example, {{chem|SO|4|2−}} is the sulfate anion, and {{chem|HSO|4|−}}, the hydrogensulfate (or bisulfate) anion. Similarly, {{chem|PO|4|3−}} is phosphate, {{chem|HPO|4|2−}} is hydrogenphosphate, and {{chem|H|2|PO|4|−}} is dihydrogenphosphate.

Oxyacids and their corresponding anions
Element group Element (central atom) Oxidation state Acid formula Acid name[7][8] Anion formula Anion name
6Chromium+6H|2|CrO|4}} Chromic acid CrO|4|2−}} Chromate
H|2|Cr|2|O|7}} Dichromic acid Cr|2|O|7|2−}} Dichromate
7Manganese +7 HMnO|4}} Permanganic acid MnO|4|−}} Permanganate
+6 H|2|MnO|4}} Manganic acid MnO|4|2−}} Manganate
Technetium +7 HTcO|4}} Pertechnetic acid TcO|4|−}} Pertechnetate
+6 H|2|TcO|4}} Technetic acid TcO|4|2−}} Technetate
Rhenium +7 HReO|4}} Perrhenic acid ReO|4|−}} Perrhenate
+6 H|2|ReO|4}} Tetraoxorhenic(VI) acid ReO|4|2−}}Rhenate(VI)
+5HReO|3}} Trioxorhenic(V) acid ReO|3|−}} Trioxorhenate(V)
H|3|ReO|4}} Tetraoxorhenic(V) acid ReO|4|3−}} Tetraoxorhenate(V)
H|4|Re|2|O|7}} Heptaoxodirhenic(V) acid Re|2|O|7|4−}} Dirhenate(V)
8Iron +6H2FeO4Ferric acidFeO42–Ferrate
Ruthenium +6H2RuO4Ruthenic acidRuO42–Ruthenate
+7HRuO4Perruthenic acidRuO4–Perruthenate (note difference in usage compared to osmium)
+8H2RuO5Hyperruthenic acidHRuO5–Hyperruthenate[10]
Osmium +6H6OsO6Osmic acidH4OsO62–Osmate
+8H4OsO6Perosmic acidH2OsO62–Perosmate (note difference in usage compared to ruthenium)
13Boron+3H|3|BO|3}} Boric acid
(formerly orthoboric acid)[9] 		BO|3|3−}} Borate
(formerly orthoborate)
(HBO|2|)|n}} Metaboric acid BO|2|−}} Metaborate
14 Carbon +4 H|2|CO|3}} Carbonic acid CO|3|2−}} Carbonate
Silicon+4H|4|SiO|4}} Silicic acid
(formerly orthosilicic acid)[9] 		SiO|4|4−}} Silicate (formerly orthosilicate)
H|2|SiO|3}} Metasilicic acid SiO|3|2−}} Metasilicate
14, 15 Carbon, nitrogen +4, −3 HOCN Cyanic acid OCN|−}} Cyanate
15Nitrogen+5HNO|3}} Nitric acid NO|3|−}} Nitrate
HNO|4}} Peroxynitric acid NO|4|−}} Peroxynitrate
H|3|NO|4}} Orthonitric acid NO|4|3−}} Orthonitrate
+3HNO|2}} Nitrous acid NO|2|−}} Nitrite
HOONO Peroxynitrous acid OONO|−}} Peroxynitrite
+2 H|2|NO|2}} Nitroxylic acid NO|2|2−}} Nitroxylate
+1 H|2|N|2|O|2}} Hyponitrous acid N|2|O|2|2−}} Hyponitrite
Phosphorus+5H|3|PO|4}} Phosphoric acid
(formerly orthophosphoric acid)[9] 		PO|4|3−}} Phosphate
(orthophosphate)
HPO|3}} Metaphosphoric acidPO|3|−}} Metaphosphate
H|4|P|2|O|7}} Pyrophosphoric acid
(diphosphoric acid) 		P|2|O|7|4−}} Pyrophosphate
(diphosphate)
H|3|PO|5}} Peroxomonophosphoric acid PO|3|3−}} Peroxomonophosphate
+5, +3 (HO)|2|POPO(OH)|2}} Diphosphoric(III,V) acid O|2|POPOO|2|2−}} Diphosphate(III,V)
+4 (HO)|2|OPPO(OH)|2}} Hypophosphoric acid
(diphosphoric(IV) acid) 		O|2|OPPOO|2|4−}} Hypophosphate
(diphosphate(IV))
+3H|2|PHO|3}} Phosphonic acid PHO|3|2−}} Phosphonate
H|2|P|2|H|2|O|5}} Diphosphonic acid P|2|H|2|O|3|5−}} Diphosphonate
+1 HPH|2|O|2}} Phosphinic acid (hypophosphorous acid) PH|2|O|2|−}} Phosphinate (hypophosphite)
Arsenic +5 H|3|AsO|4}} Arsenic acid AsO|4|3−}} Arsenate
+3 H|3|AsO|3}} Arsenous acid AsO|3|3−}} Arsenite
16Sulfur+6H|2|SO|4}} Sulfuric acid SO|4|2−}} Sulfate
H|2|S|2|O|7}} Disulfuric acid S|2|O|7|2−}} Disulfate
H|2|SO|5}} Peroxomonosulfuric acid SO|5|2−}} Peroxomonosulfate
H|2|S|2|O|8}} Peroxodisulfuric acid S|2|O|8|2−}} Peroxodisulfate
+5 H|2|S|2|O|6}} Dithionic acid S|2|O|6|2−}} Dithionate
+5, 0 H|2|S|x|O|6}} Polythionic acids
(x = 3, 4…) 		S|x|O|6|2−}} Polythionates
+4H|2|SO|3}} Sulfurous acid SO|3|2−}} Sulfite
H|2|S|2|O|5}} Disulfurous acid S|2|O|5|2−}} Disulfite
+4, 0 H|2|S|2|O|3}} Thiosulfuric acid S|2|O|3|2−}} Thiosulfate
+3 H|2|S|2|O|4}} Dithionous acid S|2|O|4|2−}} Dithionite
+3, −1 H|2|S|2|O|2}} Thiosulfurous acid S|2|O|2|2−}} Thiosulfite
+2 H|2|SO|2}} Sulfoxylic acid (hyposulfurous acid)SO|2|2−}} Sulfoxylate (hyposulfite)
+1 H|2|S|2|O|2}} Dihydroxydisulfane S|2|O|2|2−}}
0 HSOH}} Sulfenic acid HSO|−}} Sulfinite
Selenium +6 H|2|SeO|4}} Selenic acid SeO|4|2−}} Selenate
+4 H|2|SeO|3}} Selenous acid SeO|3|2−}} Selenite
Tellurium+6H|2|TeO|4}} Telluric acid TeO|4|2−}} Tellurate
H|6|TeO|6}} Orthotelluric acid TeO|6|6−}} Orthotellurate
+4 H|2|TeO|3}} Tellurous acid TeO|3|2−}} Tellurite
17Chlorine +7 HClO|4}} Perchloric acid ClO|4|−}} Perchlorate
+5 HClO|3}} Chloric acid ClO|3|−}} Chlorate
+3 HClO|2}} Chlorous acid ClO|2|−}} Chlorite
+1 HClO Hypochlorous acid ClO|−}} Hypochlorite
Bromine +7 HBrO|4}} Perbromic acid BrO|4|−}} Perbromate
+5 HBrO|3}} Bromic acid BrO|3|−}} Bromate
+3 HBrO|2}} Bromous acid BrO|2|−}} Bromite
+1 HBrO Hypobromous acid BrO|−}} Hypobromite
Iodine+7HIO|4}} Periodic acid IO|4|−}} Periodate
H|5|IO|6}} Orthoperiodic acid IO|6|5−}} Orthoperiodate
+5 HIO|3}} Iodic acid IO|3|−}} Iodate
+1 HIO Hypoiodous acid IO|−}} Hypoiodite
18Xenon +6H2XeO4Xenic acidHXeO4–Hydrogenxenate (dibasic xenate is unknown)
+8H4XeO6Perxenic acidXeO64–Perxenate

Sources

  • {{Cite book | first1 = Antti | last1 = Kivinen | first2 = Osmo | last2 = Mäkitie | title = Kemia | publisher = Otava | location = Helsinki, Finland | year = 1988 | language = Finnish | isbn = 951-1-10136-6}}
  • {{Cite book | title = Nomenclature of Inorganic Compounds, IUPAC Recommendations 2005 (Red Book 2005) | publisher = International Union of Pure and Applied Chemistry | year = 2005 | isbn = 0-85404-438-8 | url = http://old.iupac.org/publications/boox/rbook/Red_Book_2005.html}}{{dead link|date=October 2013}}
  • {{Cite book | title = Otavan suuri ensyklopedia, volume 2 (Cid-Harvey) | publisher = Otava | year = 1977 | location = Helsinki, Finland | language = Finnish | isbn = 951-1-04170-3}}

See also

  • Strong acid
  • Weak acid
  • Electronegativity
  • Hypohalous acid
  • Sulfur oxoacid

References

1. ^{{cite book|url=http://goldbook.iupac.org/I02949.html|title=IUPAC Compendium of Chemical Terminology|first=International Union of Pure and Applied|last=Chemistry|date=|publisher=IUPAC|website=iupac.org|doi=10.1351/goldbook.I02949}}
2. ^1 2 3 4 5 6 Kivinen, Mäkitie: Kemia, p. 202-203, chapter=Happihapot
3. ^{{Cite book | title = Otavan iso Fokus, Part 2 (El-Io) | pages = 990 | chapter = Hapot | publisher = Otava | year = 1973 | isbn = 951-1-00272-4}}
4. ^Otavan suuri Ensyklopedia, s. 1606, art. Happi
5. ^Otavan suuri Ensyklopedia, s. 1605, art. Hapot ja emäxet
6. ^1 Red Book 2005, s. 124, chapter IR-8: Inorganic Acids and Derivatives
7. ^1 2 3 4 Kivinen, Mäkitie: Kemia, p. 459-461, chapter Kemian nimistö: Hapot
8. ^1 Red Book 2005, p. 129-132, table IR-8-1
9. ^1 2 3 Red Book 2005, p. 132, note a
10. ^{{Cite book|url=https://www.worldcat.org/oclc/656362152|title=Encyclopedia of electrochemical power sources|last=|first=|date=2009|publisher=Academic Press|others=Garche, Jürgen., Dyer, Chris K.|year=|isbn=0444527451|location=Amsterdam|pages=854|oclc=656362152}}

External links

  • IUPAC definition of "oxoacid" (from the Gold Book)

2 : Acids|Oxoacids
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