Formic acid, dissociation constants

The acid dissociation constant for formic acid is listed in Table 8.2 ... 

Buxton GV, Sellers RM (1973) Acid dissociation constant of the carboxyl radical. Pulse radiolysis studies of aqueous solutions of formic acid and sodium formate. J Chem Soc Faraday Trans 1 69 555-559... 

The acid dissociation constant of the carboxyl radical CO2H (pK = 1.4) has been determined from an analysis of the results of a pulse-radiolysis study of aqueous solutions of formic acid and the formate anion. ... 

Fig. 19.7. Relationship between acid dissociation constant pK and frequency (v) of the antisymmetric stretching vibration of salts of carboxylic acids in DjO solution. 1, Trifluoroacetic 2, trichloroacetic 3, dichloroacetic 4, cyanoacetic 5, chloroacetic 6, 2-phenoxypropionic 7, methoxyacetic 8, formic 9, glycollic 10, lactic 11, 3-hydroxybutyric 12, acetic 13, propionic 14,cyclohexane carboxylic 15, polyacrylic 16, malonic 17, phthalic 18, benzoic 19, salicylic and 20. polyguluronic. polygalacturonic, galacturonic, alginic, hyaluronic, and chondroitin sulfates A, B, and C. ( C) From Goulden and Scott, 1968 (O) from Chapman et at. 1964. The pK values are from references given in Goulden and Scott (1968). (Goulden and Scott, 1968.)...

Formic and levulinic acids are other weak ctuboxylic acids (dissociation constants 3.75 and 4.4 respectively), which are found in hydrolyzates. Formic acid is most likely formed from degradation of HMF (56, 57), although other parallel formation routes are possible. Formic acid is a stronger inhibitor than acetic acid (57), and acts inhibitory to the fermentation process above a concentration of about 1 g/1 (58). Levulinic acid is a degradation product of HMF (56), and was shown to have a negative effect on fermentability of the hydrolyzates (57). However, due to the low concentration of formic and levulinic acid normally found in hydrolyzates, they are probably of secondary importance with respect to inhibitory effects. 

Errors may occur in the Gran titration procedure if weakly acidic species with dissociation constants (expressed as pKd) in the range of the extract pH are present. In particular, curvature or reduction (or both) of the slope of the Gran exponential plot results (24), because weak acid dissociation and titration of released free acidity take place during the portion of the titration used for end-point determination. Fortuitously, some of the common, weak carboxylic acids (e.g., formic and acetic) are not stable toward microbial decomposition when collected in aerosol samples from the atmosphere, so much of the historical data base on strong acid content of aerosols does not suffer from this positive error source, unless of course the microbial processes produce additional strong acids. 

Plot the pH-neutralization curves for 0.1 N solutions of (i) formic acid and (ii) phenol, by a strong base. Use the dissociation constants given in Problem 1. 

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. 

The hydrolysis of ammonium formate will be considered next. A solution of this salt will have an acid reaction since formic acid is a stronger acid than ammonia is a base. The dissociation constants are ... 

Formic and Acetic Acids. The solubility equilibrium of these weak acids js treated as the two stage process described by Equations 2 3. The dissociation constants of both acids are well known and are given as functions of temperature in Table III. While there are several studies of the thermodynamics of aqueous acetic acid, e.g. (2 , and of formic acid (22), there are relatively few data for dilute aqueous solutions at 25 C (28-3Ik The chemistry of these acids is complicated by dimerisation (31-33) and higher association reactions (24) in both aqueous and gas phases. 

Calculate the value of the equilibrium constant for the dissociation of formic acid (HCHO2) if the hydrogen ion concentration in... 

Nitrous and formic acids have higher dissociation constants than those calculated for them. These acids are not generally classed... 

Acetic acid has a higher Henry s law coefficient (8800 M atm-1 at 298 K) than formic acid but dissociates less (dissociation constant 1.7 x 10 5 M at 298 K). The overall result is that for pH values lower than 4, acetic acid is more soluble than formic acid. However, above pH 4 formic acid is more soluble due to its more efficient dissociation. 

Bell RP and Miller WBT, Dissociation constants of formic acid and d-formic acid, Trans. Farad. Soc., 59,1147-1148 (1963). 

Hydrogen cyanide exhibits physical and chemical properties that typify both inorganic cyanide and nitrile. It is a very weak acid the magnitude of dissociation constant is on the same order as that of amino acids. It is also a nitrile of formic acid and exhibits many reactions similar to nitriles. However, becanse its toxicology is similar to that of alkali cyanides, HCN is discussed in this chapter. 

Formic acid melts at 8.40°C and has a cryoscopic constant Ac = 1.932 K kg mol". These results of J. Lange were obtained by a Beckmann cooling-curve technique in which a differential apparatus gave values of freezing point depression for which a precision of 0.0001 K was reported. Formic acid has a dielectric constant of 58.5 at 16°C and results for potassium chloride, potassium picrate and tetramethylam-monium chloride were fitted to an extended Debye-Hiickel equation for completely dissociated electrolytes. Tetramethylammonium chloride showed the smallest deviation from the limiting law and this was ascribed to the affinity of the organic cation for the solvent. 

R.P. Bell and J.E. Crooks, Secondary hydrogen isotope effect in the dissociation constant of formic acid, Trans. Faraday Soc. 58 (1962), pp. 1409-1411. 

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