Oxoacids and their salts

Structures and values for important sulfur oxoacids are given in Table 16.8. 

Although we show the structure of dithionous acid in Table 16.8, only its salts are known and these are powerful reducing agents. Dithionite is prepared by reduction of 

The very long S—S bond in [8304] (compare 2 x rcov(S) = 206 pm) shows it to be particularly weak and this is consistent with the observation that undergoes rapid exchange between [8304] and SO3 in neutral or acidic solution. The presence of the [803] radical anion in solutions of Na38304 has been demonstrated by E8R spectroscopy (see Box 20.1). In aqueous solutions, [8304] is oxidized by air but in the absence of air, it undergoes reaction 16.98. 

Worked example 16.4 Selenium and tellurium oxides and their derivatives 

Structure 16.50 shows a representation of [Te30eF3]. Rationalize why the coordination environment of the Te atom is not tetrahedral. 

The formation of Te—F and three Te—O bonds (terminal and two bridging O atoms) adds four more electrons to the valence shell of Te. 

Within the VSEPR model, a trigonal bipyramidal coordination environment is expected. 

Draw a resonance stmcture for Se40i2 (16.51) that is consistent with selenium retaining an octet of electrons. 

Another point to notice in Table 18.2 is that any given halogen oxoacid is a better oxidizing agent—that is, has a higher standard reduction potential—than its corresponding oxoanion. Take the HOCl/OCH case as typical. Equation (18.28) shows the half-equation for hypochlorous acid in acid solution  

Suppose base (in the form of hydroxide, OH ) were to be added to this system. In which direction would the equilibrium shift The base would combine not only with the hypochlorous acid to produce hypochlorite but also with the hydrogen ion, thereby decreasing its concentration. Therefore, by Le Chatelier s principle, the reaction should be less spontaneous to the right and the E° less positive. The standard reduction potential for hypochlorite to chloride in basic solution [shown in Equation (18.29)] is 0.89 V, the lower value being consistent with the above reasoning. 

In [Te30gF3], each Te centre is surrounded by five electron pairs, of which one is a lone pair. 

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It should be emphasized that not all the processes in these schemes represent viable syntheses, and other routes are frequently preferred. The following sections give a fuller di.scussion of the individual oxoacids and their salts. 

The preparative chemistry and technical applications of the halogen oxoacids and their salts have been actively pursued and developed for over two centuries (p. 790) and can now be very satisfactorily systematized in terms of general... 

Antimony(V) Oxide and Derivatives 28.1L3.1 Antimony oxoacids and their salts... 

The oxoacids and their salts are very stable, in contrast to the lack of stability of the halogen oxides themselves. A large number of these acids exist at the representative oxidation states of the halogens, namely, +1, +3, +5, and +7. Even perbromic acid, HBr04, has been synthesized by fluorination ofbromates. 

Many of the sulfur oxoacids and their salts are connected by oxidation-reduction equilibria some of the more important standard reduction potentials are summarized in Table 15.19 and displayed in graphic form as a volt-equivalent diagram (p. 435) in Fig. 15.28. By use of the couples in Table 15.19 data for many other oxidation-reduction equilibria can readily be calculated. (Indeed, it is an instructive exercise to check the derivation of the numerical data... 

Oxoacids and their salts Aqueous solution chemistry... 

OCCURRENCE, PROPERTIES, AND USERS Table 28-5 Halogen Oxoacids and Their Salts... 

Oxides and hydroxides Oxoacids and their salts Compounds containing nitrogen Metal borides Borane and carbaborane clusters... 

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