Successive acidity constants table

Table 4.5 Successive acidity constants of polyprotic acids at 298.15 K...

Protons are donated successively by polyprotic acids, with the acidity constant decreasing significantly, usually by a factor of about 10 , with each proton lost (Table 10.9) ... 

The definition of pH is pH = —log[H+] (which will be modified to include activity later). Ka is the equilibrium constant for the dissociation of an acid HA + H20 H30+ + A-. Kb is the base hydrolysis constant for the reaction B + H20 BH+ + OH. When either Ka or Kb is large, the acid or base is said to be strong otherwise, the acid or base is weak. Common strong acids and bases are listed in Table 6-2, which you should memorize. The most common weak acids are carboxylic acids (RC02H), and the most common weak bases are amines (R3N ). Carboxylate anions (RC02) are weak bases, and ammonium ions (R3NH+) are weak acids. Metal cations also are weak acids. For a conjugate acid-base pair in water, Ka- Kb = Kw. For polyprotic acids, we denote the successive acid dissociation constants as Kal, K, K, , or just Aj, K2, A"3, . For polybasic species, we denote successive hydrolysis constants Kbi, Kb2, A"h3, . For a diprotic system, the relations between successive acid and base equilibrium constants are Afa Kb2 — Kw and K.a Kbl = A w. For a triprotic system the relations are A al KM = ATW, K.d2 Kb2 = ATW, and Ka2 Kb, = Kw. 

The small difference between the successive pK values (cf. values below) of tungstic acid was previously explained in terms of an anomalously high value for the first protonation constant, assumed to be effected by an increase in the coordination number of tungsten in the first protonation step (2, 3, 55). As shown by the values of the thermodynamic parameters for the protonation of molybdate it is actually the second protonation constant which has an abnormally high value (54, 58). An equilibrium constant and thermodynamic quantities calculated for the first protonation of [WO, - pertaining to 25°C and zero ionic strength (based on measurements from 95° to 300°C), namely log K = 3.62 0.53, AH = 6 13 kJ/mol, and AS = 90 33 J, are also consistent with a normal first protonation (131) (cf. values for molydate, Table V). 

Table 2 shows combinations of solvent and non-solvent suitable to fractionate CA using SSF 39 - 42). For the fractionation of CTA, acetic acid and chlorinated hydrocarbons, which have a low dielectric constant e, have been used extensively. Unfortunately, the fractionation efficiency achieved with these solvents was poor, and numerous attempts made so far have met with very limited success 43). Judging from the easiness of two-liquid phase separation and of solvent recovery, Kamide et al. 39) chose l-chloro-2,3-epoxy-propane (epichlorohydrine) as a solvent and heptane as a precipitant. 

That is, the acid involved in each successive step of the dissociation is weaker. This is shown by the stepwise dissociation constants given in Table 7.4. These values indicate that the loss of a second or third proton occurs less readily than the loss of the first proton. This result is not surprising the greater the negative charge on the acid, the more difficult it becomes to remove the positively charged proton. 

EDTA, the abbreviation for ethyldiaminotetraethyl acid, usually is identified as H4Y. When dissolved at different pH values it exists in different forms. In strong acid solutions (pH < 1), it exists primarily as HgY. In the pH range of 2.67-6.16 it exists mainly in the form. At a pH > 10.26, it exists mainly in the Y form. The pH value employed for the separation of RE elements with EDTA as the chelate displacer is the key to a successful operation. The RE elements can be separated by using EDTA because the stability constants of the complexes they form are different. These stability constants increase with the increasing atomic number of the RE elements. In the steady-state zones obtained for the RE elements in the course of their separation, the pH value in each element separation zone is sizably different. The more stable the complex, the lower is the pH. Conversely, the less stable the complex, the higher is the pH. The pH values associated with some of the RE elements in their respective steady-state zones are listed in Table 8. 

When [V,iV dialky]-o-nitroanilincs are heated or photolysed in acidic media, good yields of benzimidazole W-oxides (60) can be obtained (Scheme 2.1.25). The thermal reactions usually require high temperatures (above 100°C) and extended heating times (often 12-48 h), but the reactions arc versatile and simple experimentally. Refluxing in constant-boiling hydrochloric acid is usually successful, giving yields in the range 30-70% even with NJV-cycloalkyl derivatives [158-160]. Table 2.1.10 lists some examples. 

Similar results were obtained with a commercial trimetallic Pd-Pt-Bi/C catalyst engaged in 5 successive tests the normalized gluconic acid yield measured after each catalytic test remains constant. Bi losses are less extensive during the first operation but proceed further throughout the first five experiments (table 5). Perhaps the presence of Pt in the catalyst can account for this slightly different behaviour under the reaction conditions. 

The rate of oxygen exchange of a series of substituted benzoic acids was also studied by Gragerov and Ponomarchuk (1959) (see Table 7) who attempted to correlate the rate of exchange with the dissociation constants of the acids without much success. The rates of exchange (Gragerov and Ponomarchuk, 1959) fall in the following order ... 

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