2-Oxoacid

Many of the inorganic oxoacids are strong (i.e. have negative PX3 values) in aqueous solution. But, as we have seen, use of a solvent with a lower proton affinity than water (for example pure ethanoic (acetic) acid makes it possible to differentiate between the strengths of these acids and measure pX values. The order of strength of some typical oxoacids is then found to be (for H X -> H , X- + H") ... 

Graphite reacts rather differently with mixtures of oxidising agents and concentrated oxoacids. A graphite oxide is formed the graphite... 

Non-metals — These are often oxidised to the corresponding oxoacid, and nitrogen oxide is formed. For example, sulphur gives sulphuric acid with cold concentrated nitric acid ... 

Phosphorus forms a large number of oxoacids, many of which cannot be isolated but do form stable salts. In general, ionisable hydrogen is bonded to the phosphorus through an oxygen atom hydrogen atoms attached directly to phosphorus are not ionisable. 

X-Ray diffraction studies of the oxoacid anions indicate the following probable arrangements for the acids ... 

With concentrated nitric acid, selenium and tellurium form only their +4 oxoacids, H2Se03 and H2Te03 respectively, indicating a tendency for the higher oxidation states to become less stable as the atomic number of the element is increased (cf. Group V, Chapter 9). 

Replacement of Oxygen by Other Chalcogens. Acids derived from oxoacids by replacement of oxygen by sulfur are called thioacids, and the number of replacements are given by prefixes di-, tri-, and so on. The affixes seleno- and telluro- are used analogously. 

Regularities in the observed strengths of oxoacids have been formulated in terms of two rules by L. Pauling and others ... 

The results for dinuclear and polynuclear oxoacids are also consistent with this interpretation. Thus for phosphoric acid, H4P2O7, the successive p/fa values are 1.5, 2.4, 6.6 and 9.2 the 10-fold decrease between p/f and p/f2 (instead of a decrease of 10 ) is related to the fact that ionization occurs from two different PO4 units. The third stage ionization, however, is less than the first stage and the differ-... 

Other oxoacid salts of the alkali metals are discussed in later chapters, e.g. borates (p. 205), silicates (p. 347), phosphites and phosphates (p. 510), sulfites, hydrogensulfates, thiosulfates, etc. (p. 706) selenites, selenates, tellurites and tellurates (p. 781), hypohalites, halites, halates and perhalates (p. 853), etc. 

Other oxoacid salts and binary compounds are more conveniently discussed under the chemistry of the appropriate non-metals in later chapters. 

Compounds of Tl have many similarities to those of the alkali metals TIOH is very soluble and is a strong base TI2CO3 is also soluble and resembles the corresponding Na and K compounds Tl forms colourless, well-crystallized salts of many oxoacids, and these tend to be anhydrous like those of the similarly sized Rb and Cs Tl salts of weak acids have a basic reaction in aqueous solution as a result of hydrolysis Tl forms polysulfldes (e.g. TI2S3) and polyiodides, etc. In other respects Tl resembles the more highly polarizing ion Ag+, e.g. in the colour and insolubility of its chromate, sulfide, arsenate and halides (except F), though it does not form ammine complexes in aqueous solution and its azide is not explosive. 

The reversible intercalation of various oxoacids under oxidizing conditions leads to lamellar graphite salts some of which have been known for over a century and are now particularly well characterized structurally. For example, the formation of the blue, first-stage compound with cone H2SO4 can be expressed by the idealized equation... 

Oxoacid salts of Ge are usually unstable, generally uninteresting, and commercially unimportant. The tetraacetate Ge(OAc)4 separates as white needles, mp 156°, when GeCl4 is treated with TlOAc in acetic anhydride and the resulting solution is concentrated at low pressure and cooled. An unstable sulfate Ge(S04)2 is formed in a curious reaction when GeCl4 is heated with SO3 in a sealed tube at 160° ... 

Numerous oxoacid salts of Sn and Sn have been reported and several basic salts are also known. Anhydrous Sn(N03)2 has not been prepared but the basic salt Sn3(0H)4(N03)2 can be made by reacting a paste of hydrous tin(II) oxide with aqueous HNO3 the compound may well contain the oligomeric cation [Sn3(OH)4] + illustrated on p. 384, Sn(N03)4 can be obtained in anhydrous reactions of... 

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