Silver selenites

The accepted experimental determinations of the solubility product of silver selenite defined by the equilibrium  

The review selects the average of the first four log K values in the Table and obtains  

The uncertainty has been chosen rather large as systematic errors cannot be excluded in some of the measurements. 

Mehra and Gubeli [68MEH], [69MEH/GUB] made extensive measurements of the solubility of Ag2SeO ,(s) in aqueous solutions at 298.15 K as a function of pH and total selenite concentration. From these measurements, which are presented and evaluated in Appendix A, the review accepts the results log /f, ((V.l 14), 1 M NaCI04, 298.15 K) =- (15.40 + 0.35) and the stability constant of the reaction  

Selivanova, Leshchinskaya, and Klushina [62SEL/LES] measured the enthalpy change when crystalline silver selenite was formed from AgN03(cr) and a solution of sodium selenite in a calorimetric experiment. Their result is used in Appendix A to estimate the standard enthalpy of formation of Ag2Se03(cr) to be Af//° (Ag2Se03, cr, 298.15 K) = - (363.44 1.02) kJ-mol. This value agrees well with [82WAG/EVA] but differs appreciably from the result in the paper, - 345.0 kJ-moE.  

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Sixteen years later, Ekmann and Pettersson 8 estimated the silver in pure silver selenite by ignition and the selenium in the pu.re dioxide by reduction with sulphurous acid from its solution in dilute hydrochloric acid. The results were ... 

The following year Julius Meyer reverted to the analysis of silver selenite. The analysis, however, was made by electrolytic deposition of the silver from a solution of the salt in potassium cyanide 2... 

Bromine oxidises silver selenite according to the equation... 

Silver selenite decomposes on heating following the reaction scheme Ag2Se03(cr or 1) 2Ag(cr) + Se02(g) + 0.502(g)... 

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. 

The authors also measured the enthalpy change of the reaction between AgN03(cr) and a solution of sodium selenite with formation of crystalline silver selenite as verified by chemical analysis and X-ray diffraction. The calorimeter was calibrated by electrical resistance heating. The calorimetric data are evaluated in Table A-25. 

BAK/BUK2] Bakeeva, S. S., Buketov, E. A., Pashinkin, A. S., Dissociation pressure of silver selenite, Russ. J. Inorg. Chem., 13, (1968), 16-17. From a citation in this Bibliography... 

MEH/GUB] Mehra, M. C., Gubeli, A. O., Complexing characteristics of insoluble selenites 1. Silver selenite, Radiochem. Radioanal. Lett., 2, (1969), 61-68. Cited on pages 303, 304, 514. 

Cray, hexagonal, microscopic needles, mp 880. d<5 8.216. Two forms exist transition temp at 133. Forms metallic silver and selenium oxide when heated in oxygen transformed by chlorine into silver and selenium chlorides oxidized to silver selenite by fuming nitric acid. So] in mol ten silver or bismuth without chemical change. Practically insol in water. 

Dissolve 10 grams of selenium dioxide in 150 ml of water and stir thoroughly while adding a solution of 32 grams of silver nitrate in 120ml of water. When the precipitate has settled, pour off the mother liquor and nearly neutralize it with concentrated sodium carbonate solution. A further quantity of the fairly soluble silver selenite is obtained. Wash this precipitate once by decantation and add it to the main quantity of the precipitate. 

Wash the combined precipitate once by decantation and then with ice water on the Buchner funnel until the washings give no test for silver. If it is necessary to leave the silver selenite at this point, cover it with water do not let it dry out. 

Suspend the washed silver selenite in 500 ml of water and stir thoroughly with a mechanical stirrer having a glass paddle. Add slowly the theoretical amount of bromine for the reaction... 

Selenic acid has been prepared in a number of ways, all of which are laborious, and only a few of which yield the concentrated acid in a state of high purity. Several authors " have prepared solutions of heavy-metal selenates and then precipitated the metal with hydrogen sulfide to give a dilute solution of the acid. The selenates were usually prepared by oxidation of the corresponding selenites with chlorine. Others have oxidized suspensions of silver selenite with free halogen, then precipitated the silver halide to yield dilute solutions of selenic acid that could be concentrated by evaporation. Still othes have electrolyzed solutions of selenates to effect removal of metallic ions, but this method has never been... 

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