Solubility Products and Solubility Concepts

Abstract

The chapter refers to a general concept of solubility product K sp of sparingly soluble hydroxides and different salts and calculation of solubility of some hydroxides, oxides, and different salts in aqueous media. A (criticized) conventional approach, based on stoichiometry of a reaction notation and the solubility product of a precipitate, is compared with the unconventional/correct approach based on charge and concentration balances and a detailed physicochemical knowledge on the system considered, and calculations realized according to generalized approach to electrolytic systems (GATES) principles. An indisputable advantage of the latter approach is proved in simulation of static or dynamic, two-phase nonredox or redox systems. Descriptive Inorganic Chemistry Researches of Metal Compounds 94an organized manner-not just imitative, but focused on heuristics. This viewpoint is in accordance with constructivist teaching, based on the belief that learning occurs, as learners are actively involved in a process of meaning and knowledge construction, as opposed to passively receiving information [19]. Definitions and formulation of solubility productsThe K sp value refers to a two-phase system where the equilibrium solid phase is a sparingly soluble precipitate, whose K sp value is measured/calculated according to defined expression for the solubility product. This assumption means that the solution with defined species is saturated against this precipitate, at given temperature and composition of the solution. However, often a precipitate, when introduced into aqueous media, is not the equilibrium solid phase, and then this fundamental requirement is not complied, as indicated in examples of the physicochemical analyses of the systems with struvite MgNH 4 PO 4 [20, 21], dolomite CaMg(CO 3 ) 2 [22, 23], and Ag 2 Cr 2 O 7 .The values of solubility products K sp (usually represented by solubility constant pK sp = ÀlogK sp value) are known for stoichiometric precipitates of A a B b or A a B b C c type, related to dissociation reactions:where A and B or A, B, and C are the species forming the related precipitate; charges are omitted here, for simplicity of notation. The solubility products for more complex precipitates are unknown in the literature. The precipitates A a B b C c are known as ternary salts [24], e.g., struvite, dolomite, and hydroxyapatite Ca 5 (PO 4 ) 3 OH.

Struvite as a Non-Equilibrium Solid Phase in Electrolytic Systems (Aqueous Media)

“…Although the fact that NH 3 evolves from the system obtained after leaving pure pr1 in pure water [2]. 3pr1 = pr2 + HPO 4 -2 + 2NH 4 +1 + NH 3 (1) has already been known at the end of 19 th century (see [2][3][4][5][6]) the solubility (s, mol/L) of pr1was commonly calculated from the approximate formula s = (K sp1 ) 1/3 (see e.g. [7]), based on an assumption that pr1 is the equilibrium solid phase in such a system.…”

GATES/GEB as the Best Thermodynamic Approach to Electrolytic Redox Systems - a Review

“…The paper refers to fundamental/general regularities obligatory for electrolytic systems. The linear combination f 12 = 2•f(O) -f(H) of elemental balances: f 1 = f(H) for Y 1 = H and f 2 = f(O) for Y 2 = O, is the general, key relation distinguishing between electrolytic redox and non-redox systems in aqueous media [1][2][3][4][5][6][7].…”

“…It is stated that f 12 is (1 o ) linearly independent on f 0 ,f 3 , …,f K for a redox system, or (2 o ) linearly dependent on f 0 ,f 3 ,…,f K when related to a non-redox system, and thus the independency/dependency property of f 12 (3 o ) provides a rigorous criterion distinguishing between redox and non-redox systems [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. As the independent balance for a redox system, (4 o ) f 12 is considered as the primary form of Generalized Electron Balance (GEB).…”