Selenite ion

H2Se (hydrogen selenide, colorless), HSe (acid telluride ion, colorless), Se (selenide ion, colorless), H2Se03 (selenous acid, colorless), HSeOJ (acid selenite ion, colorless), SeO (selenite ion, colorless), H2Se04 (selenic acid, colorless), HSeOJ (acid selenate ion, colorless), SeO " (selenate ion, colorless). 

The free selenite ion has a pyramidal shape (C3v symmetry) owing to the lone electron pair at the selenium atom. Thus, the Se032- ion can be treated as a pseudo-tetrahedral anion and the lone electron pair often acts as an invisible ligand within the crystal structures of selenites. This observation is called the stereochemical activity of the lone electron pair and it will turn out as one of the... 

For Elg2Se03 three modifications have been described.133 They all contain dumbbell-shaped EIg22+ ions that are linked by the selenite ions. A common feature of all crystal structures is the formation of channels, which obviously incorporate the lone electron pairs of the selenite ions. 

Also mercury(II) selenite is polymorphic and two new modifications, p-HgSe03 and y-HgSe03, have been recently described.134 They show the mercury atoms in sevenfold coordination of oxygen atoms, and the [I Ig07] polyhedra are linked by the pyramidal selenite ions. A remarkable and unusual mercury selenite is the mixed valent compound (HgSe03)3E[gSe.134 As a characteristic feature, the crystal structure contains [Hg3Se] pyramids with distances Hg Se of 2.489 A. 

The selenite and sdenate ions illustrate the effect of oxidation state on adsorption behaviour. The selenite ion (SeO ) adsorbs strongly and specifically on goethite and shifts the iep of both goethite and ferrihydrite to lower pH values (Su and Suarez,... 

Monteil-Rivera, F., Masset, S., Dumonceau, J., Fereroff, M. Jeanjf.an, J. 1999. Sorption of selenite ions on hydroxyapatite. Journal of Materials Science Letters, 18, 1143-1145. 

In a previously mentioned work by Kirlew et al., electrophoretic separations of Se, Se As As, and dimethylarsinic acid were performed using various ultrasonic nebulizer (USN) interfaces. Using the optimized CE interface conditions and a borate run buffer at pH 8, a separation was accomplished within 10 min. Electrokinetic injections gave better sensitivities for the analytes as compared to hydrostatic sample injection. In the Kirlew study, arsenate and selenite ions had very similar migration times, but these analytes were easily resolved by the multielement capability of the ICP-MS detector. An electropherogram of this work is shown in Fig. 5. In an application to field samples. Van Holderbel ... 

Selenates and Selenites.—The separation of selenate and selenite ions by circular paper chromatography has been described.299 The significance of... 

Elements of Group VI suitable eluents and the migration behaviour of selenate and selenite ions was brought out, and a method for the clear separation of the ions by the technique of precipitation chromatography described. 

Elements of Group VI up to 0.07 mole% Se02 into the gas phase. The low-temperature decomposition of the selenite ion is thought to involve the participation of the water of hydration since these water molecules are strongly distorted by the field of the cations and anions. The dissociation pressure of zirconium diselenite has been measured.316... 

Figure 5. Evidence for surface species (right) in the normalized, background-subtracted, k3-weighted EXAFS spectra (left) of selenate and selenite ions reacted with goethite. The EXAFS spectra of selenate or selenite ions in aqueous solution are shown as dashed curves, with vertical arrows denoting contributions from Fe(III) in the selenite spectrum. Reactive surface OH groups on goethite are...

Most work on the determination of the protonation constants of the selenite ion ... 

The procedure outlined above is fairly typical for a number of determinations of solubility products of metal selenites. Data from such investigations have been reevaluated by the review with the accepted protonation constants of the selenite ion, corrected for the hydrolysis of the metal ion when necessary, and the value of the solubility product extrapolated to standard state conditions. It has been observed that the initial and final pH values in cases are in conflict. This has been ignored and the calculations have been based solely on the data for the equilibrium solution. Complexation of the metal ion by the anions and temperature effects were neglected, which probably introduces a negligible error compared with other sources of error. Activity coefficients were calculated by the SIT expression with s = 0 kg-mol, which is a reasonable simplification due to the low ionic concentrations. The ionic strength was obtained by an iterative procedure from knowledge of the total metal concentration and the pH of the equilibrium solution. The results of the recalculations are entered in Chapter V. 

Only the protolysis of the selenite ion was considered in the evaluation of the measurements, which are presented in Table A-11 and Table A-12. The protonation... 

The activity product was calculated with the accepted protonation constants of the selenite ion using the SIT approach for the activity coefficient correction. The value of Ag/AgjSeOj obtained from m was (309.5 18.9) mV with a systematic trend in the value with m. The value from iv was -(137.4 + 3.5) mV with no significant trend. Hence a reversal of the sign of the potentials from cell (I) is indicated. The values were calculated with qqh = 699.4 mV. With ° = 799.1 mV the corresponding solu-... 

Pyatniskii and Durdyev measured the solubility of CoSe03-2H20 in water and as a function of the total selenite concentration at a pH of about 8.5. The temperature of the experiments is not mentioned. The primary data of the water solubility, which included the pH of the equilibrium solutions, have been used in a recalculation that yielded logid= -(8.1710.05), for the reaction CoSe03-2H20(cr) Co + SeO,"+ 2H2O. The result in the paper is - 7.64 calculated with an unspecified value of the protonation constant of the selenite ion. 

The ionic conductivity of the selenite ion in water was determined by measuring the molar conductivities of a series of aqueous solutions of lithium selenite with concentrations below 2 x 10" M. The molar conductivity at infinite dilution was found by extrapolation to be (172.0 2.9) ohm -cm mor. With the ionic conductivity of Li equal to 33.4 ohm -cm -mor, the ionic conductivity of the selenite ion becomes 105.2 ohm -cm -moT. This value was then combined with the ionic conductivity of the metal ion to find the molar conductivity of the dissolved selenite. 

Masson points out that the protolysis of the selenite ion was not taken into account in the determination of the ionic conductivity of the selenite ion or in the evaluation of the solubility product. An entirely satisfactory correction cannot be found for this omission. However, as pointed out by Masson, because the calibration and sample... 

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