Equilibrium constants sulfuric acid complexes

For this equilibrium, the ion product constant has a value of approximately 2.7 X 1CP4. However, the discussion is complex and other species are present in sulfuric acid as a result of equilibria that can be written as... 

It is necessary to consider a number of equilibrium reactions in an analysis of a hydrometallurgical process. These include complexing reactions that occur in solution as well as solubility reactions that define equilibria for the dissolution and precipitation of solid phases. As an example, in analyzing the precipitation of iron compounds from sulfuric acid leach solutions, McAndrew, et al. (11) consider up to 32 hydroxyl and sulfate complexing reactions and 13 precipitation reactions. Within a restricted pH range only a few of these equilibria are relevant and need to be considered. Nevertheless, equilibrium constants for the relevant reactions must be known. Furthermore, since most processes operate at elevated temperatures, it is essential that these parameters be known over a range of temperatures. The availability of this information is discussed below. 

PK. A measurement of the complete ness of an incomplete chemical reaction. It is defined as the negative logarithm ito the base 101 of the equilibrium constant K for the reaction in question. The pA is most frequently used to express the extent of dissociation or the strength of weak acids, particularly fatty adds, amino adds, and also complex ions, or similar substances. The weaker an electrolyte, the larger its pA. Thus, at 25°C for sulfuric add (strong acid), pK is about -3,0 acetic acid (weak acid), pK = 4.76 bone acid (very weak acid), pA = 9.24. In a solution of a weak acid, if the concentration of undissociated acid is equal to the concentration of the anion of the acid, the pAr will be equal to the pH. 

The parameters of the Michaelis-Menten type kinetics were calculated for the reactions and are summarized in Table II. The apparent Michaelis constant values (Km) are rather large, indicating that the concentration of the complex at the equilibrium state is not high, unlike ordinary enzymatic reactions. The ratio of kJKm against the second-order rate constant with sulfuric acid (k2) can be considered to be an indication of the rate enhancement. The ratio increased with increasing mole fraction of the vinyl alcohol repeating unit in the copolymer and with... 

Plants in the UK, USSR and France are now reprocessing irradiated UO2/PUO2 fuels and LMFBR fuel reprocessing has been the subject of international conferences. " The plant at Cap la Hague, France, employs a 30% TBP solution and no U/Pu separation is undertaken, so that a mixed U/Pu product is obtained. Fluoride is added to the process feed to complex zirconium and suppress its extraction." The Dounreay plant in the UK employs a 20% TBP/OK solution and uses sulfuric acid to effect the U/Pu separation. TBP poorly extracts Pu or U from sulfuric acid solutions, but in mixed HNO3/H2SO4 the equilibria shown in equations (206) and (207) must be considered. The equilibrium constants for these reactions, Kj, and K i, are given... 

The application of standard electrode potential data to many systems of interest in analytical chemistry is further complicated by association, dissociation, complex formation, and solvolysis equilibria involving the species that appear in the Nemst equation. These phenomena can be taken into account only if their existence is known and appropriate equilibrium constants are available. More often than not, neither of these requirements is met and significant discrepancies arise as a consequence. For example, the presence of 1 M hydrochloric acid in the iron(Il)/iron(llI) mixture we have just discussed leads to a measured potential of + 0.70 V in 1 M sulfuric acid, a potential of -I- 0.68 V is observed and in 2 M phosphoric acid, the potential is + 0.46 V. In each of these cases, the iron(II)/iron(III) activity ratio is larger because the complexes of iron(III) with chloride, sulfate, and phosphate ions are more stable than those of iron(II) thus, the ratio of the species concentrations, [Fe ]/[Fe ], in the Nemst equation is greater than unity and the measured potential is less than the standard potential. If fomnation constants for these complexes were available, it would be possible to make appropriate corrections. Unfortunately, such data are often not available, or, if they are, they are not very reliable. 

The thermodynamics and kinetics of NCS , CN , Cl , Br , NCS and 1 substitutions at [Rh(TPPS)(H2 O)] have been reported the reactions involved are shown in equation (169), and the parameters determined are summarized in Table 60. Spectrophotometric titrations showed two inflection points as OH is added to [Rh(TPPS)(H20)2] , and e consecutive pA values (7.01 and 9.80 at 20 °C) correspond to the pA values for fac- and /ner-[RhCl3(H20)3], suggesting that the TPPS anion and 3 Cl ligands are comparable electron donors toward the Rh center. The trends in the equilibrium constants (Table 60) imply that Rh" is a soft (class B) acid in these complexes the NCS ion is presumed to be sulfur bonded, although no direct evidence is presented to support this assumption. 

A specific feature of rigid-chain polyamides related to the possibility of dissolution of these polymers only due to the very energetic interaction of the elementary units of the polymer with the solvent molecules is manifested in these systems. At low temperatures, salt compounds crystallize out in the form of crystal solvates [42] with a constant polymer-sulfuric acid molar ratio. At high temperatures, the crystal solvate melts and equilibrium involving a liquid-crystalline phase is attained. The polymer-acid complex in this example is thermally unstable and decomposes at relatively low temperatures. Melting of the compound with decomposition— incongruent melting—results in the appear-... 

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