Second dissociation constant

H PO is therefore a stronger acid than orthophosphoric acid. The second dissociation constant, pR 2> Th third hydrogen does not ionize in... 

This value is in the range expected from an acid of structure (HO)2CO (p. 50). The second dissociation constant is given by... 

Table 9 includes data on the first dissociation constants of seven weak acids it will be recalled that we expect these to fall into class III. The table includes the second dissociation constants of five acids, phosphoric, sulfuric, oxalic, malonic, and carbonic, which fall into class IV, while the amino acids glycine and alanine provide four examples that should fall into class II. 

This means that, with increasing length of chain, the equilibrium constants K1 and K2 (the first and second dissociation constants at infinite dilution of the acid) should not tend to equality rather their ratio K1/K2 should tend toward the value 4, as recognized by Adams.1... 

Because the second dissociation constant of H2SO4 is large (ca. lO ) and because about... 

As the second dissociation constant is often much smaller than the first, a2 ( i 1 and [H2S+] = K c)m. Thus, the acid can be considered... 

Hufford et al [13] used a 13C NMR spectroscopic method for the assignments of dissociation constants of primaquine. The first and second dissociation constants of primaquine were determined by titration with 0.1 N hydrochloric acid in acetonitrile-water mixtures and values were extrapolated to water by using linear regression analysis. The assignments of the dissociation constants were unambiguously achieved by studying the 13C NMR spectral data obtained with monohydrochloride, dihydrochloride, and trihydrochloride salts. 

It is not a problem either for the protonation constant of S (i.e. the reciprocal of the second dissociation constant of H2S) some estimates of which are shown in Fig. 4. Neither Cobble s estimate (68), using the correspondence principle (curve a) nor Pohl s (69) extrapolation (curve b) using an empirical equation due to Harned and Embree (70) is showing any indication of the expected minimum in K. The extrapolation used by Khodakovskii et al (71) (curve c) is based on the more frequently used expression of Harned and Robinson (72) and a different selection of low temperature data. While their result looks more reasonable it is difficult to have much confidence in any of the results even up to 200 C. The apparent failure of the correspondence principle may arise as much from the choice of low temperature data as a failure of the relationship itself. 

All polyprotic acids, except sulfuric acid, are weak. Their second dissociation is much weaker than their first dissociation. For this reason, when calculating [HsO" ] and pH of a polyprotic acid, only the first dissociation needs to be considered. The calculation is then the same as the calculation for any weak monoprotic acid. In the Sample Problem, [HP04 ] was found to be the same as the second dissociation constant, Ka. The concentration of the anions formed in the second dissociation of a polyprotic acid is equal to... 

There is often a large variation in values from source to source— in some cases, some orders of magnitude. For diis reason, only one significant figure (at most) is given before the exponent. A table of solubility products for many sulphides based on a reevaluated value for the second dissociation constant of H2S is given in Ref. 1. The values in that study are typically some orders of magnitude lower than the ones shown here. 

The first possibility is substrate inhibition. A second molecule of substrate binds to give an ES2 complex that is catalytically inactive. If, in a simple Michaelis-Menten mechanism, the second dissociation constant is K s, then... 

With different aryl phosphates at a fixed substrate concentration an analogous set of curves is generated (155). A correlation between the second dissociation constant of the ester and the pH optimum, rate of hydrolysis, and Km value was noted With increasing pK of the substrate, the pH optimum became more neutral, the rate of hydrolysis decreased, and Km increased. With rat intestinal phosphatase and / -glycerophosphate a linear relationship was found between the logarithm of the substrate concentration and the pH optimum (158) and has since been confirmed for tissue phosphatases of several mammalian species and of poultry (156). 

Interpretation of the Second Dissociation Constant of the Esteratic Site... 

There are four reactions that deal explicitly with the H+ ion (Table 3.3) one is the dissociation constant for water (Kw), two are the first and second dissociation constants of carbonic acid (K and K2), and the fourth deals with the dissociation of the bisulfate (HSOJ) ion (iFbisuifate)-... 

Ksp is the 0aCO3 solubility product, Ku is Henry s law constant for CO2, K and K- are respectively the first and second dissociation constants for... 

During the neutralisation with alkali a sharp end-point was obtained (to methyl orange) when one equivalent of alkali had been added, while phenolphthalein gradually changed between 1-5 and 2-0 equivalents, showing that the second dissociation constant is lower than that of the majority of organic acids (see also Electrical Conductivity, p. 151). 

Only the alkalis and alkaline earths form sulfides that appear to be mainly ionic. They are the only sulfides that dissolve in water and they crystallize in simple ionic lattices, for example, an anti-fluorite lattice for the alkali sulfides and a rock salt lattice for the alkaline earth sulfides. Essentially only SH" ions are present in aqueous solution, owing to the low second dissociation constant of H2S. Although S2" is present in concentrated alkali solutions, it cannot be detected below 8 M NaOH owing to the reaction... 

Let us take maleic and fmnaric acids. The values of the first and second dissociation constants are as follows ... 

The second dissociation constant, pK2 (which involves the removal of the proton from the nitrogen atom in the process G H+ + G-), can be obtained by extrapolation of pK2 values (the apparent second dissociation constants) to zero ionic strength I, where I = m2 + ms- The pertinent equation is... 

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