Ionization constants of carbonic acid

As with other dicarboxyhc acids the second ionization constant of carbonic acid IS far smaller than the first... 

Kryukov, P.A. Starostina, L.I. Tarasenko, S.Ya Pavlyuk, L.A. Smolyakok, B.S. Larionov, E.G. "Ionization Constants of Carbonic Acid, Hydrogen Sulfide, boric Acid, and Sulfuric Acid at High Temperatures," Mezhdunar. Geokhim., Koagr. (Dokl.) 1st, 1971, 186-98 C.A, 1974, 84 (69193). 

Hamed, H. S. and Davis, R. The ionization constant of carbonic acid in water and the solubility of carbon dioxide in water and aqueous salt solutions from 0 to 50, J. Am. Chem. Soc. 2030-2037 (1943). 

Determination of hydroxyl ion in the presence of carbonate Owing to the small second ionization constant of carbonic acid K2 = 5 x 10" ), the titration of hydroxyl ion alone is not feasible in the presence of an appreciable concentration of carbonate ion. For example, a 0.01 M solution of sodium hydroxide has a pH of about 12, and a 0.01 M solution of sodium carbonate a pH of about 11.2. Thus the pH change in a titration of 0.01 M sodium hydroxide in the presence of 0.01 M sodium carbonate would be only about 0.8 pH unit. 

J. Walker and W. Cormack found the ionization constant of carbonic acid [H][HC03 J—A)2[H2C03]. J. Kendall s value for 2... 

The First Ionization Constant of Carbonic Acid. Using a method similar in principle but differing in details from that just described, Maclnnes and Belcher T have determined the first and second ionization... 

The Second Ionization Constant of Carbonic Acid. Maclnnes and Belcher also determined the second ionization constant, K2, of carbonic acid, corresponding to the equilibrium... 

The equilibrium constant of this reaction is often called the first ionization constant of carbonic acid.) Combine the h,b ionization reaction at 25.00 °C. Use solute standard states based on molality, which are also the solute standard states used for the values in Appendix H. 

In an 8-page paper, Harned and Davis (1943) discussed the ionization constant of carbonic acid in water and expressed the solubilities as Henry s law constants, H = Mco2/Pco2 Mco2 being the molality. 

If the solution being studied is one of a strong acid of concentration greater than 10" n, the ionization of the weak carbonic acid is depressed to such an extent that its contribution towards the total conductance is negligible. In these circumstances no water correction is necessary at most, the value for pure water, i.e., about 0.04 X 10" ohm" cm. at ordinary temperatures, may be subtracted from the total. If the concentration of the strong acid is less than 10" n, a small correction is necessary and its magnitude may be calculated from the dissociation constant of carbonic acid. 

As mentioned in Section IV.A, Nelson and Yang [494] have proposed a surface complexation model to describe the effect of pH on adsorption equilibria of chlorophenols on activated carbon. To account for the well known suppression of uptakes as pH increases, they introduce the ionization constants of separate acidic (A) (e.g., carboxyl) and basic (B) (e.g., pyrone) functional groups on the carbon surface ... 

In considering the structures of the organic acids, it is evident that the a-carbon atom (the one combined directly with the carboxyl group) influences the ionization constant of the acid to the greatest extent. A classification of the acids will be given which depends upon the direction of the valences by which this a-carbon atom is combined with the other atoms in the molecule, or its valence, or its oxidation potential. This divides the acids into four general classes which may be formulated as follows ... 

This is the answer to our question in 9.1 ( what happens to the reaction after it starts ). The reaction continues until the ratios of the activities of the products and reactants equals the equilibrium constant, in this case 10 . It doesn t matter what the starting activities were, and individual activities at equilibrium can be quite variable. In other words the values of anjco, and of (uhcoj h+) are not determined, nor are the values of Uecof or h+ individually only the ratio expressed by K is fixed. In specific cases, the values of these individual activities are determined by the bulk composition of the solution, and can be determined by speciation (Chapter 16). For now, we are content to determine K. In this case K is the ionization constant for carbonic acid, H2CO3. It is a very small number, meaning that carbonic acid is a weak acid. 

The three ionization constants of phosphoric acid have the values 7.5 X 10", 6.2 X 10 , and 1 X 10 . When one or two hydrogen atoms are replaced by carbon atoms of organic radicals the first two acid constants become somewhat larger, as shown by the following examples ... 

Rate constants for ionization of carbon acids (chloroform-r and acetophenone-r) in alkaline aqueous sulfolane have been determined and their dependence on solvent composition and temperature has been interpreted for this highly basic medium. °... 

Equilibrium constants for ionization reactions are usually called ionization or dissociation constants, often designated Ka. The dissociation constants of some acids are given in Figure 2-16. Stronger acids, such as phosphoric and carbonic acids, have larger dissociation constants weaker acids, such as monohydrogen phosphate (Ill Of ), have smaller dissociation constants. 

When HX is a carbon acid the value of the rate coefficient, ) for a thermodynamically favourable proton transfer rarely approaches the diffusion limit. Table 1 shows the results obtained for a few selected carbon acids which are fairly representative of the different classes of carbon acids which will be discussed in detail in Sect. 4. For compounds 1—10, the value of k i is calculated from the measured value of k, and the measured acid dissociation constant and, for 13, k, is the measured rate coefficient and k1 is calculated from the dissociation constant. For 11 and 12, both rate coefficients contribute to the observed rate of reaction since an approach to equilibrium is observed. Individual values are obtained using the measured equilibrium constant. In Table 1, for compounds 1—10 the reverse reaction is between hydronium ion and a carbanion whereas for 11, 12 and 13 protonation of unsaturated carbon to give a carbonium ion is involved. For compounds 1—12 the reverse reaction is thermodynamically favourable and for 13 the forward reaction is the favourable direction. The rate coefficients for these thermodynamically favourable proton transfers vary over a wide range for the different acids. In the ionization of ketones and esters, for which a large number of measurements have been made [38], the observed values of fe, fall mostly within the range 10s—101 0 1 mole-1 sec-1. The rate coefficients observed for recombination of the anions derived from nitroparaffins with hydronium ion are several orders of magnitude below the diffusion limit [38], as are the rates of protonation and deprotonation of substituted azulenes [14]. For disulphones [65], however, the recombination rates of the carbanions with hydronium ion are close to 1010 1 mole-1 sec-1. Thermodynamically favourable deprotonation by water of substituted benzenonium ions with pK values in the range —5 to —9 are slow reactions [27(c)], with rate coefficients between 15 and 150 1 mole-1 sec-1 (see Sect. 4.7). 

Ionization constants of 2-carboxypiperazine and the three dicarboxylic acids have been determined (1684), and the nucleophilic reactivity of piperazine compared to other amines in reactions with l-chloro-2,4-dinitrobenzene has been measured (1685). The rate of quaternization of l-ethoxycarbonyl-4-methylpiperazine with allyl bromide (/ = 2.25 1/mol min) and methyl iodide (10A = 1.22) have been measured in acetone-water solution (1686). The composition and structure of the 2-methylpiperazine-carbon disulfide complex has been investigated it was a mixture of l-dithiocarboxy-3-methylpiperazine (138) and the 2-methylpiperazine salt of l,4-bis(dithiocarboxy)-2-methylpiperazine (1687). 

Ives, Linstead and Riley 4 have made extensive studies on the effect of a double bond in the carbon chain of aliphatic acids. In general, the unsaturated acids are stronger than the saturated ones. However, the effect of the double bond decreases as it is removed from the carboxyl. These effects are shown in the results obtained by these authors quoted in Table I. The ionization constants of corresponding unsatu-... 

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