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Thermodynamic characterization of the amphoterism of oxides M2O3 (M─As, Sb, Bi) and their hydrates in aqueous mediaстатья
- Автор: Shkol'nikov E.V.
- Журнал: Russian Journal of Applied Chemistry
- Том: 83
- Номер: 12
- Год издания: 2010
- Издательство: Maik Nauka/Interperiodica Publishing
- Местоположение издательства: Russian Federation
- Первая страница: 2121
- Последняя страница: 2127
- DOI: 10.1134/S1070427210120104
- Аннотация: 1. The molar solubility of M2 O3 oxides (M - As, Sb, Bi) and their hydrates in pure water and in weakly acidic medium is determined mainly by neutral M(OH)3 complexes and decreases significantly in the transition from amorphous to stable crystalline modification. The molar solubility in water of stable crystals decreases in the series α-AsO1.5 > > α-SbO1.5 > SbOH > α-BiO1.5 > BiOOH > Bi(OH)3 . 2. The enthalpy of endothermic dissolution of As2 O3 in water increases in the series glass < arsenolite < stable claudetite. Aqueous saturated solutions of As2 O3 are weakly acidic (pH0 4.8-5.0), Sb2 O3 and hydrates are very weakly acidic (pH0 6.97-7.00), Bi2 O3 and hydrates are weakly basic (pH0 7.01-7.96). 3. The influence of pH value on the molar solubility of M2 O3 oxides and their hydrates in aqueous alkaline and acidic media at 25°C was calculated for the first time by the thermodynamic method taking into account the formation of hydroxocomplexes. The minimum solubility and pH values of the most complete precipitation of oxides and their hydrates, as well as the amphoteric parameter A>1, decreasing in the series Sb > As > Bi, were determined. 4. Calculation of thermodynamic constants of acid-base equilibria in aqueous media for crystalline oxides M2 OH3 and dissolved hydroxides M(OH)3 indicates the presence of weak base properties, increasing in the series As(OH)3 < < < Sb(OH)3 < Bi(OH)3 . In amphoteric oxides and hydroxides of antimony(III), weak acidic properties predominate over very weak base properties. The predominantly acidic oxide As2 O3 and the predominantly basic one
- Добавил в систему: Школьников Евгений Васильевич