First dissociation constant

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. 

The following table gives the values of K for the first dissociation constant of... 

Statistical Effects. In a symmetrical diprotic acid, the first dissociation constant is twice as large as expected since there are two equivalent ionizable... 

In a similar investigation of the tautomeric tridentate ligand 2 -hydroxyphenylazo-2-naphthol (5.65 in Scheme 5.17), the first and second acidic dissociation constants (pKa) related to the two hydroxy groups in the parent structure (X = H) were found to be 11.0 and 13.75 respectively. On introduction of an electron-withdrawing substituent (X) the first dissociation constant decreased from 11.0 to 10.55 (X = Cl) or 7.67 (X = N02). The stability constants (log K1 1) of the derived 1 1 complexes were dependent on the metal ion introduced [46], being particularly high for nickel(n) at 19.6 and copper(II) at 23.3. 

The first dissociation constant for the -CO2H group is the more acidic group with a pK of 1.8 to 2.4. This group in amino acids is substantially more acidic than acetic acid, which has a... 

Colorless gas strong garlic-like odor stable to light when dry but undergoes photochemical decompostion in the presence of moisture and dust density 5.68 g/L liquefies to a colorless unstable liquid at -2°C, decomposed by light liquid density 2.57 g/mL at -20°C solidifies at -49°C soluble in water, alcohol and alkalies pKa 2.6 (for first dissociation constant at 18°C) and 11.0 (the dissociation constant at 25°C) for the second replaceable hydrogen. 

The acid has four replacable H+ ions. Its dissociation constants indicate that two H+ ions are strongly acidic while the other two protons are weakly acidic. The first dissociation constant especially is very large ... 

The bipyridines are dibasic, and the two acid dissociation constants Ki and K2, for all the bipyridines have been determined. Typical values are recorded in Table I. There has been considerable interest in the first dissociation constants Ki of 2,2 -bipyridine and substituted 2,2 -bipyridines because of their use as metal complexing agents. In general, the order of relative basic strengths of derivatives of 2,2 -bipyridine is as expected. Electron-attracting substituents reduce the basicity, whereas electron-donating substituents increase the basicity of the molecule. " The dissociation constants of several substituted bipyridines correlate well with the Hammet equation. 2,2 -Bipyridines with an electron-donating substituent at position 4 are monoprotonated at N-1 and not at... 

Statistical effects. In a symmetrical diprotic acid, the first dissociation constant is twice as large as expected since there are two equivalent ionizable hydrogens, while the second constant is only half as large as expected because the conjugate base can accept a proton at two equivalent sites. So K IKi should be 4, and approximately this value is found... 

The thermodynamic first dissociation constant for H2S at infinite dilution can be determined from ( )... 

Measurements of the first dissociation constant for HjS in seawater have been made by a number of workers. The measurements of Savenko (12) and Goldhaber and Kaplan (2Q) were made using the National Bureau of Standards (N.B.S.) pH scale (21)... 

A detailed analysis of the course of the first dissociation constant of boric acid in H20-D20 mixtures (Gold and Lowe, 1968) leads to the unexpected conclusion that of the equations... 

Thus, k = k2K2/(KsK]) if aHC0(s) - aHC0- at equilibrium, if, is the first dissociation constant of carbonic acid. Equation (136) becomes... 

The equilibrium quotient in the first equation is not really correct. It assumes that all C02 dissolved and undissociated is present as H2C03, which is not true. In fact, the greater part of the dissolved C02 is only loosely hydrated, so that the correct first dissociation constant, using the true activity of H2C03, has a value of about 2 X 10 4, which is more nearly in agreement with expectation for an acid with the structure (HO)2CO. 

First Dissociation Constants of Organic Acids in Aqueous Solution at 298 K The values are shown in Table 16.6. 

It was pointed out in the preceding chapter that phosphoric acid is a weak acid, its first dissociation constant being 0.75 X I0 2. it a stable substance, without effective oxidizing power. 

The first dissociation constant takes the value -6.88 0.02 20 °C, but the second has given... 

The first acids of the sulfuric acid system to be recognized (29) were disulfuric acid, H2S2O7, and the higher polysulfuric acids, H2SSO10 etc., which are present in oleum. Dilute oleum contains mainly disulfuric acid, H2S2O7, and from cryoscopic measurements on such solutions the first dissociation constant of disulfuric acid has been found to be 1.4 X 10 2 (5). It is approximately 30% ionized in a 0.1 m solution ... 

Dissolved in water, maleic acid is a very strong organic acid. Its first dissociation constant at 25 °C is Ki = 1.42 x 10 mole/liter (pKi = 1.83) as compared to K = 1.77 x lO" mole/liter (pK = 3.75) for formic acid. 

Equations (4.7) and (4.8) can be combined to eliminate [H2CO3] and give a new composite first dissociation constant of CO2 in seawater. If one assumes that [C02(aq)j = [CO2], the first dissociation constant of carbonic acic, K l, is... 

It is interesting that the presence of a charged atom in a molecule induces a fractional charge not only on the other atoms of the chain but also on those atoms which are near by in space. Thus if the electrostatic attraction were conducted only through the carbon skeleton of a molecule, we should expect to find the dissociation constants of fumaric and maleic acids to be identical. In actual fact the first dissociation constants are somewhat similar, but there is a considerable difference in the second dissociation constants. A possible explanation of this phenomenon is that in the case of the mono acid salts of maleic acid, the near-by negative charge on the carboxylate group hinders the removal of the second proton. 

Table 1 Henry s law constants and first dissociation constants for atmospheric gases that undergo hydrolysis (25°C). 

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