Magnesium selenites

The solubility product of magnesium selenite has been determined in a number of studies in which the solid phase has been denoted as MgSe03. The review assumes that the determinations pertain to the hexahydrate and writes  

Chukhlantsev [56CHU] measured the solubility in dilute solution of nitric or hydrochloric acid at 293 K. The data have been recalculated as described in Appen- 

The review selects the result obtained by Savenko [95SAV] as the most reliable and calculates at standard conditions  

Leshchinskaya and Selivanova [66LES/SEL] measured the enthalpy change of the reaction between Na2Se03(cr) and a solution of magnesium sulphate with formation of MgSe03-6H20(cr). Their data have been re-evaluated in Appendix A with new auxiliary data and a minor correction for incomplete conversion in the studied reaction. The result is  

Leshchinskaya and Selivanova [66LES/SEL] prepared MgSe03(cr) and measured the enthalpy of dissolution of MgSe03(cr), -(70.00 + 0.17), and MgSe03-6H20(cr), 

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K4H6O10P2 potassium pyrophosphate trihydrate 7320-34-5 25.00 2.3300 1 2419 MgHl209Se magnesium selenite hexahydrate 15593-61-0 25.00 2.0900 1... 

The authors reacted 9 x 10 moles of MgS04(aq, 1 2000) with an equivalent amount of Na2Se03(cr) in 325 grams of water in an electrically calibrated calorimeter. Crystalline MgSe03 6H20 was formed. From the solubility product of magnesium selenite the review estimates that about 6% of the Mg remained in solution after the reaction. A correction has been applied, which changes the enthalpy of Reaction 1 in Table A-51 from - (47.49 0.13) in the paper to - (48.25 0.25) kJ-mol. ... 

EBE/HAV] Ebert, M., Havlicek, D., Magnesium selenites, Chem. Zvesti, 34, (1980), 441 -451. Cited on page 394. 

Li2Si03 LITHIUM METASILICATE 983 MgSe03 MAGNESIUM SELENITE 1029... 

In order to balance mineral intake, the following minerals were used in place of the usual mineral mix (% of diet) potassium chloride, 0.32 magnesium oxide, 0.084 manganous carbonate, 0.0123 ferric nitrate, 0.021 zinc carbonate, 0.0056 cupric carbonate, 0.0011 potassium iodate, 0.0004 sodium selenite, 0.00003 chromium potassium sulfate, 0.00193. 

The selenides may also be obtained by direct combination of the elements, either by passing selenium vapour over the heated metal in a vacuum or by heating the metal with selenium in a crucible, the reaction being started by means of a magnesium fuse.3 In the case of potassium the reaction is explosive. The compounds may also be obtained by the action of hydrogen selenide on the heated metal,4 on the heated metallic chloride or its vapour, preferably in the presence of nitrogen,5 or by reduction with hydrogen or carbon of an oxysalt such as a selenite.6 Selenides have also been prepared by electrolytic methods.7... 

The primary solubility data and the calculation of the solubility products, defined in the usual way, are presented. This presentation contains some unexpected results. The total solubility of the metal ion and selenite are approximately equal in water and in the inert salt solutions for the magnesium and manganese selenites. This is the expected result for a simple dissolution reaction. For calcium selenite, the metal ion concentration was about 100 times greater than the total selenite concentration whereas for zinc selenite the opposite was found. There is no comment in the paper on these results, which contradict the equilibrium reactions used in the paper to define the reported solubility products for calcium and zinc selenite. The review also noted that the calculation of the magnesium and selenite activities from the total concentrations introduces activity coefficients between 0.1 to 0.01 at moderate ionic strengths. Thus the values of these coefficients appear unreasonably small. On the whole, the activity coefficient corrections introduced appear to vary in an erratic way between the various systems studied. 

Savenko, V. S., Solubility product of magnesium and calcium selenites, Zh. Neorg. Khim., 40, (1995), 1254-1256, in Russian, English translation in [95SAV2]. Cited on pages 395, 400. 

Selenate apparently is not converted to dimethyl selenide as readily as is selenite. Studies of selenate metabolism are limited in mammals, but studies using bacteria indicate that selenate must be activated prior to conversion to selenite (Bopp et al. 1982). Dilworth and Bandurski (1977) demonstrated that in the presence of ATP, magnesium (II) salts, and ATP-sulfurylase, yeast could convert selenate to eventually yield selenite (Figure 3-6). Data regarding the metabolism of selenium sulfide after administration to humans or other animals were not located in the literature. 

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