Acid dissociation constants oxoacids

For some elements with varying oxidation states, series of oxoacids with different numbers of oxygen atoms may exist (Table 7.3). There is no adequate thermodynamic treatment for rationalizing the observed trends within a series, but there are certain empirical methods for estimating The best known of these is Bell s rule (eq. 7.31) which relates the first acid dissociation constant to the number of hydrogen-free O atoms in an acid of formula EO (OH) . 

Table 6.7 Approximate acid dissociation constants of the oxoacids of chlorine ...

All known investigations of the relative acidic properties of ionic melts are based just on the determination of the equilibrium constants of reaction (1.3.6) in these media. Since the applicability of these data for estimating the equilibrium parameters and conditions was not checked experimentally, there was no reason to doubt the correctness of the use of equilibrium (1.3.6) as an indicator one for f estimations. Indeed, we shall now consider the data presented in Ref. [169], where the acidic properties of the KCl-LiCl eutectic at 600 °C were investigated using equilibrium (1.3.6). The shift of the oxoacidity scale as compared with the KCl-NaCl equimolar mixture was found to be close to 8. Such a considerable difference in acidities for KCl-NaCl and KCl-LiCl melts is unexpected, since the index of the Li20 dissociation constant (pK) ... 

In addition to the tetrahedral HIO4, another oxoacid of iodine in the +7 oxidation state with an expanded octet is possible. H5IO6, usually called orthoperiodic acid, has an octahedral array of oxygen atoms linked together by hydrogen bonds. Orthoperiodic acid is a weak acid as shown by the dissociation constants in Equations (18.45) and (18.46) ... 

Let us analyze the experimental data on oxoacidity investigations in KCl-LiCl eutectic melts and their agreement with predictions on the basis of Q value,which was estimated as ca. 8. Such a considerable difference in acidities for KCl-NaCl and KCl-LiCl melts is unexpected since the index of Li20 dissociation constant (pK) ... 

Strengths of oxoacids can be affected by many variables. For example, you may wonder how acidity depends on oxidation number, or how it varies across a row of the Periodic Table. There is also the question of the relationship between the first, second, etc., dissociation constants of polybasic acids. 

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