Sodium selenite solution preparation

Chukhlantsev and Tomashevsky [57CHU/TOM] prepared lead selenite by mixing an acidified 0.2 M solution of lead acetate and a 0.1 M sodium selenite solution in stoichiometric amounts. The precipitate was crystalline. Chemical analysis confirmed the 1 1 ratio between Pb(Il) and Se(IV). No X-ray diffraction measurements were performed. The solubility of the specimen in dilute solution of nitric or hydrochloric acid was measured at 293 K. The experiments were performed and the data recalculated as described in Appendix A, [56CHU]. The result for ... 

Many problems occur in Se-speciation analysis, owing e.g. to risks of adsorption on container walls, instability of species or contamination, insufficient separation efficiency of the chromatographic techniques, problems of conversion yield of selenite to selenate etc. Prior to conducting an interlaboratory project on this topic, it was hence decided to assess the stability of selenite and selenate according to various factors (effects of container materials, additives, temperature and light). The study focused on tests of effects of physicochemical parameters on solutions stored in polyethylene and PTFE containers. Container volumes were 100 and 500 mL for polyethylene and 500 and 1000 mL for PTFE. Stock and initial working solutions were prepared in 1 and 5 L polyethylene containers previously cleaned with nitric acid (at pH 2) and rinsed with Milli-Q water. The stock solutions were prepared with sodium selenite and sodium selenate (purity >98%). 

The selenites were generally prepared by mixing a 0.1 to 0.2 M solution of the metal ion and a 0.1 M solution of sodium selenite in stoichiometric proportions. In some cases the precipitate was aged in the mother liquor before separation and drying. The specimens were analysed but only the ratio metahselenium is reported. X-ray diffraction patterns were not registered. It is therefore not clearly established whether the preparations were crystalline or (aged) amorphous phases. 

Silver selenite was prepared by addition of a selenious acid solution to a solution of silver nitrate. The product was recrystallised three times from nitric acid ( ). Sodium hydrogen selenite solution was prepared by neutralisation of recrystallised selenious acid by carbonate-free sodium hydroxide. The silver-silver selenite electrodes were obtained by first electroplating silver onto a platinum foil and then converting some of the silver to silver selenite by further anodic electrolysis. The procedure was apparently the same as used for the preparation of silver-silver chloride electrodes. The experiments were carried out in the dark or in subdued daylight. 

Nickel selenite was prepared by mixing 0.1 M solutions of sodium selenite and nickel nitrate in stoichiometric proportions at room temperature. The amorphous precipitate crystallised on boiling the reaction mixture for 2 hours. X-ray diffraction showed that the preparation was crystalline and chemical analysis agreed with the formula NiSe03-2H20. 

Sodium hydrogen selenite was prepared and the specimen checked by X-ray and chemical analysis. The enthalpy of reaction between solid NaHSe03 and a solution of lead nitrate with formation of crystalline lead selenite was measured in an electrically calibrated calorimeter. The result is used in Table A-67 to calculate the enthalpy of the reaction NaHSe03(cr) + Pb -> PbSe03(cr) + + Na. ... 

Crystalline sodium trihydrogen selenite was prepared and reacted in stoichiometric proportions with a solution of lead nitrate in an electrically calibrated calorimeter. The lead selenite formed was crystalline and the reaction was quantitative. The calorimetric data have been used to calculate the enthalpy change of the reaction NaH3(Se03)2(cr) + 2Pb 2PbSe03(cr) + Na -i- 3H in Table A-74. 

Sodium diselenite was prepared from NaHSeOs by heating at 383 K. The quality of the specimen was controlled by X-ray and chemical analysis. The salt was reacted with a solution of lead nitrate in an electrically calibrated calorimeter with formation of crystalline lead selenite. The enthalpy change of the reaction Na2Se205(cr) + H20(l) -i-2Pb 2PbSe03(cr) + 2Na + 2H is estimated in Table A-75. 

Crystallise sodium selenite from a saturated aqueous solution where its solubility is 68% at 20 to give the pentahydrate salt. This yields the anhydrous salt on heating at 40 . [Feh6r in Handbook of Preparative... 

Sodium selenite [10102-18-8] M 172.9, m >350", pK 2.62, pK 8.32 (for H2Se03). Crystallise sodium selenite from a satorated aqueous solution where its solubility is 68% at 20" to give the pentahydrate salt. This yields the anhydrous salt on heating at 40°. [Feher in Handbook of Preparative Inorganic Chemistry (Ed. Brauer) Academic Press Vol I p 431 1963. ... 

Two concentration levels of selenite and selenate solutions were prepared a low concentration solution of 6 gg selenite + selenate (solution A) and a high concentration solution of 50 pgL selenite + selenate (solution B). Sodium chloride (2000 mg L ) was added to stabilize the inorganic species (at pH 6). 

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