The study of the dissolution reaction of the silicium and germanium dioxides was carried out in the NaOH-KOH (49 mole91 eutectic mixture at 2 l O O C and in pure NaOH at 350'C.The initial acidobasicity of these solvents as well as the Cg2-and CH20 modifications after addition of the Si(1V) and Ge(1V) solutes were measured by M original method using linear sweep voltammetry at a platinum electrode. This procedure was nevertheless ineffective in acidic NaOH medium because of the diotortion of the water reduction peak by the cathodic front. In this case, the water liberated by the reaction was eliminated by a flow of dry nitrogen and collected in a cell containing anhydrous MgClO .

This paper describes the chemical behavior of tin (II) and (IV) in the eutectic mixture normalNaOH‐KOH (49M%) at 483 K and in molten normalNaOH at 623 K. Sn(II) is unstable in molten hydroxides and is oxidized by the solvent. The oxidation of normalSnO occurs either directly in the solid phase or after dissolution as SnO22− . Basic conditions promote the liquid phase oxidation. Sn(IV) dissolves as SnO32− in the eutectic mixture. Soluble in basic melts, it is only slightly soluble in acidic melts and precipitates as Na2SnO3 false(normals=6.8+0.6×10−4Mfalse) at water concentrations <4.10−2 M and as a mixture of SnO2 and Na2SnO3 in more acidic media. Sn(IV) is practically insoluble in acidic sodium hydroxide false(normals<10−6Mfalse) and precipitates as Na2SnO3 . It dissolves in basic melts as SnO44− false(s<10−3Mfalse) , Na4SnO4 being precipitated from saturated solutions.

013ChemInform Abstract In molten hydroxides, Sn(II) is unstable and is converted to Sn(IV) at a rate which depends on the temp. and on the acid-base properties of the melts. The oxidation of SnO occurs either directly in the solid phase or after dissolution as SnO22-. Basic conditions promote the liquid phase oxidation. In the NaOH-KOH eutectic mixture, Sn(IV) dissolves as SnO32-, which is insoluble in acidic melts and precipitates as Na2SnO3 upon acidification of a basic solution. In basic melts, Sn(IV) dissolves as SnO44-and Na4SnO4 precipitates from saturated solutions.

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