Dissociation Constant Of Acetic Acid Research Articles

Biostimulant Potential of Acetic Acid Under Drought Stress Is Confounded by pH-Dependent Root Growth Inhibition.

Recent reports of acetic acid-induced drought tolerance and avoidance across a diverse range of plant species encourage consideration of this low-cost commodity organic acid as a biostimulant. These results are surprising as they contrast with earlier studies showing pH-dependent root growth inhibition at similar concentrations. We test the hypothesis that the concentration of the membrane permeable undissociated form of acetic acid (CH3COOH) selectively inhibits maize root growth, and subsequently evaluate its impact on seedling water use and growth under deficit irrigation. We demonstrate conclusively for the first time that when germinating maize on filter paper, low pH exacerbates, and high pH mitigates, this inhibition of root growth in a predictable manner based on the dissociation constant of acetic acid. The buffering capacity of potting media can reduce this root damage through keeping the acetic acid primarily in the membrane impermeable dissociated form (CH3COO–) at near neutral pH, but peat substrates appear to offer some protection, even at low pH. While both deficit irrigation and acetic acid reduced water use and growth of maize seedlings outdoors, there was no significant interaction between the treatments. Twenty nine millimolar total acetic acid (CH3COOH + CH3COO–) reduced transpiration, compared to lower and higher concentrations, but this did not specifically improve performance under reduced water availability, with parallel declines in shoot biomass leading to relatively consistent water use efficiency. Any acetic acid biostimulant claims under water stress should characterize its dissociation level, and exclude root damage as a primary cause.

Determination of chloroacetic acids in water by capillary zone electrophoresis with field-amplified sample injection

ABSTRACTA simple and sensitive method has been developed for the determination of chloroacetic acids and acetic acid in water using capillary zone electrophoresis under modified electroosmotic flow with indirect UV detection. Potassium hydrogen phthalate at pH 5.40 was used as background electrolyte (BGE), and hexadecyltrimethylammonium bromide was used as electroosmotic flow modifier. Field-amplified sample injection (FASI) method was used to enhance the sensitivity. Results showed that the limit of detection for these analytes was enhanced more than 15-fold and the repeatabilities were good with relative standard deviations (RSDs %) of migration time and corrected peak areas being below 0.33%, 4.45% (intra-day) and 0.87%, 9.67% (inter-day), respectively. An off-line liquid–liquid extraction (LLE) process with methyl tert-butyl ether was carried out to detect these compounds in water samples. The dissociation constants of acetic acid and monochloroacetic acid (MCA) were determined with two methods and the results obtained were consistent with the reference values.

Dissociation Constant of Acetic Acid in (N,N-Dimethylformamide + Water) Mixtures at the Temperature 298.15 K

In the present work the thermodynamic dissociation constants of acetic acid were determined in (N,N-dimethylformamide (DMF) + water) mixtures over the DMF mole fraction range from 0 to 0.65 at the temperature 298.15 K by the potentiometric titration method. The dissociation constant in pure DMF was obtained by extrapolation and comparative calculation methods. The dependence of the acetic acid dissociation constant on the mixed solvent composition was fitted with linear multiple regression of the solvatochromic parameters of (DMF + water) mixtures at every studied composition.

Determination of Stoichiometric Dissociation Constants of Acetic Acid in Aqueous Solutions Containing Acetic Acid, Sodium Acetate, and Sodium Chloride at (0 to 60) °C

Equations were determined for calculation of stoichiometric (molality scale) dissociation constants Km of acetic acid in buffer solutions containing acetic acid, sodium acetate, and sodium chloride from determined thermodynamic dissociation constants Ka of this acid at temperatures from (0 to 60) °C, and molalities of components in solution. These equations were based on single-ion activity coefficients obtained by Hückel-type equations. The thermodynamic dissociation constants and acetate parameters required were determined from the Harned cell data of Harned and Ehlers. The interaction parameter between neutral acetic acid molecules and acetate ions was determined from Harned cell data for unbuffered aqueous mixtures of acetic acid and NaCl at 25 °C, and the resulting value applied to all temperatures. The interaction parameters between hydrogen ions and chloride ions were taken from the recent data reassessment by Partanen and Covington. The parameters resulted from interactions between hydrogen ions and sodium ions and between sodium and chloride ions were determined from the Harned cell data measured by Harned for aqueous mixtures of HCl and NaCl. The resulting equations were tested with literature data for cells both with and without a liquid junction at various temperatures. The new equations predict well the literature data used in the tests. The new parametric equations were used to check the pH values of 0.01 molal acetate and 0.1 molal acetate buffers recommended by IUPAC for temperatures from (0 to 60) °C, and agreement was usually found to be within ±0.005. Calculated p(mH) values are also tabulated for buffer solutions containing NaCl as the major component and acetate species as minor components for calibration glass electrode cells for direct measurement, particularly in potentiometric titrimetry, of hydrogen ion molality.

Comparison of different methods for calculation of the stoichiometric dissociation constant of acetic acid from results of potentiometric titrations at 298.15 K in aqueous sodium or potassium chloride solutions

Single-ion activity coefficient equations were determined for the calculation of the molality-scale dissociation constants, K m, for acetic acid in aqueous NaCl or KCl solutions at 298.15 K. The salt alone determines the ionic strength, I m, of the solutions considered in this study. The activity coefficient equations are of the Hückel type, and K m can be calculated by those for a certain ionic strength from the thermodynamic dissociation constant. The data used for the estimation of the parameters for these equations were measured by potentiometric titrations in a glass electrode cell. Three different methods to calculate the experimental K m values from the titration data were considered. The activity parameters for the Hückel equation were determined from the K m values calculated by all of these methods. The parameters obtained by these methods are very consistent with each other and also with the Hückel parameters obtained previously for acetic acid from the literature data measured on Harned cells. The final activity parameters recommended in this study seem to be reliable. Despite the theoretical difficulties associated with the single-ion activity coefficients and the simplicity of the calculation method based on Hückel equations, K m can be obtained by this method almost within experimental error for acetic acid in NaCl and KCl solutions up to I m of about 1 mol kg −1. It was shown in this study, in addition, that the K m values obtained by the Hückel equations agree well also with those calculated by the Pitzer equations.

Dissociation constants of acetic acid in acetone + water mixture

Dissociation constants of acetic acid in acetone + water mixture

Dissociation Constant of a Weak Electrolyte in Charged Membrane

In this study, the dissociation constant of acetic acid as a weak electrolyte in an ion-exchange membrane, Κ, was estimated using the Donnan equilibrium theory, which has been applied to a strong polyelectrolyte membrane. The membrane charge density and the total concentration, which represents the sum of the dissociated proton concentration and carboxyl concentration of the undissociated electrolyte in the membrane, were determined by neutral titration; the charge effectiveness was determined from membrane potential measurements; and the proton concentration in the external solution phase was determined by Donnan equilibrium theory and used for the calculation of Κ. The dissociation constants, Κ, in the cation exchange membrane were on the order of 10-4 and were larger than that in water (= 1.73 × 10-5). The value of Κ increased with an increase in the concentration in the external solution and decreased with the fixed charge density increase. It is suggested that the fixed charge group depresses the dissociation of the weak electrolyte.

Potentiometric Determination of the Dissociation Constants of Some Monocarboxylic Acids in Various Hydroorganic Media

The dissociation constant of acetic acid, benzoic acid, 3-phenylpropenoic acid, 2-methylpropionic acid, and pentanoic acid were determined at 25.0 °C (I = 0.1 mol dm -3 KNO 3 ) by potentiometric pH titration in pure water and water + methanol, water + ethanol, water + dimethylformamide, water + dimethyl sulfoxide, and water + acetonitrile. pK a values increase with an increase in the concentration of the organic compounds. These results are discussed in terms of solvent characteristics. Solvent basicity and stabilization of the conjugate acid free base by hydrogen-bonding interactions in hydroorganic solvent media relative to pure aqueous media as well as proton-solvent interaction play an important role in the acid dissociation equilibrium.

Determination of the Molality Scale Dissociation Constants of Acetic Acid in Aqueous Sodium Chloride Solutions at 298.15 K.

Determination of the Molality Scale Dissociation Constants of Acetic Acid in Aqueous Sodium Chloride Solutions at 298.15 K.

The dissociation kinetics of rare earths-N-methylethylenediamine-N,N′,N′-triacetate complexes

The dissociation kinetics of lanthanide-N-methylethylenediamine-N,N′,N′-triacetate (MEDTA) complexes have been studied in aqueous acetic acid/ sodium acetate solutions using Cu 2+ ions as sequestring agent. The reaction mechanism involves a fast protonation equilibrium ( K H) of a mixed complex Ln-MEDTA-OAc −, followed by a slow rate determining internal proton transfer ( k s) ▪ where K a is the acid dissociation constant of acetic acid and K M the stability constant of the mixed complexes Ln-MEDTA-OAc. K M values increase and the product k s K H decreases with decreasing ionic radii of the trivalent rare earths. Formal rate constants for the formation reaction are calculated from the dissociation rate and the stability of the mixed complex; however, this reaction is too fast to be followed by the stopped-flow spectrometer.

Dissociation Constants of Acetic Acid in Methanol- Water Media at Different Temperatures and Related Thermodynamic Quantities

Dissociation Constants of Acetic Acid in Methanol- Water Media at Different Temperatures and Related Thermodynamic Quantities

Dissociation Constants of Acetic Acid in Methanol- Water Media at Different Temperatures and Related Thermodynamic Quantities

Dissociation Constants of Acetic Acid in Methanol- Water Media at Different Temperatures and Related Thermodynamic Quantities

Potentiométrie de précision à basse température dans les mélanges eau – éthylène glycol; grandeurs thermodynamiques relatives aux ionisations de l'acide acétique et du solvant mixte

Electromotive force measurements of cells without liquid-junction containing hydrogen electrodes and silver – silver chloride electrodes have been used to derive the dissociation constants of acetic acid and solvent water – ethylene glycol mixtures (50 and 70 mass % of ethyleneglycol) at 14 temperatures from −35 to 30 °C. Primary acidity standards related to these acetic buffered and sodium hydroxide solutions are given.

Dissociation Constants of Acetic Acid and Protonated Tris(Hydroxymethyl)‐Aminomethane in 80 mass% 2‐Methoxyethanol/20 Mass % Water in the Range 10 to 50°

AbstractElectromotive‐force measurements of cells without transference have been used to determine the thermodynamic dissociation constants of acetic acid and protonated Tris (hydroxymethyl)aminomethane (Tris.H+) in the mixed solvent 80 mass% 2‐methoxyethanol/20 mass% water from 10 to 50°. Hydrogen gas electrodes and silver‐silver chloride electrodes were used. Thermodynamic constants for the dissociation process were derived. The enthalpy of dissociation of Tris.H+ was also determined by titration calorimetry and found to be in acceptable agreement with the value obtained from the emf measurements. Allowance for association of the ions of the salts used altered the calculated pK values by about 0.03 unit (acetic acid) and 0.06 unit (Tris.H+).

Dissociation constants of acetic acid and primary phosphate ion and standards for pH in 10, 20, and 40 wt % ethanol/water solvents at 25, 0, -5, and -10.degree.C

Dissociation constants of acetic acid and primary phosphate ion and standards for pH in 10, 20, and 40 wt % ethanol/water solvents at 25, 0, -5, and -10.degree.C

Conductance of HCl, NaCl, Na acetate, and acetic acid in water-ethylene carbonate solvent mixtures at 25 and 40�C

The molar conductances of solutions of hydrochloric acid, sodium chloride, sodium acetate, and acetic acid were measured in water-ethylene carbonate (EC) solvent mixtures at 25 and 40°C. These solvents have dielectric constants higher than that of water. Four solvent compositions, in which the mole fraction (x2) of EC was 0.2, 0.4, 0.5, and 0.6, were studied at 25°C. For HCl and acetic acid at 40°C, additional measurements were made atx2=0.8 and 1.0. Analysis of the data by the Pitts equation was successful up tox2=0.6 and for HCl tox2=0.8. A graphical method, together with Λ0 derived from the measurements for HCl, NaCl, and NaAc, yielded the dissociation constant of acetic acid up tox2=0.6. As EC is added, all the compounds studied displayed increased ion association. The acidic strength of acetic acid is greatly reduced; the dissociation constant atx2=0.6 is only 1/1000 that in water. The behavior of these electrolytes reflects the poor solvating power of EC, and the dielectric constant plays only a minor role.

Dissociation of acetic acid in 50 mass % ethylene carbonate-water from 20 to 55�C

The dissociation constant of acetic acid in 50 mass % ethylene carbonate-water solvents has been determined at eight temperatures from 20 to 55°C by emf measurements of cells without liquid-junction containing hydrogen electrodes and silver-silver chloride electrodes. Acetic acid is weaker in the mixed solvent than in pure water. At 25°C, pK is 5.645 as compared with 4.756 in water, in spite of the fact that the dielectric constants of the two media do not differ materially. Standard changes in Gibbs energy, enthalpy, entropy, and heat capacity for the dissociation processes at 25°C were evaluated. The decrease in acidic strength when ethylene carbonate is added to the water medium appears to be largely the results of a destabilization of the two ionic species, especially a partial desolvation of the hydrogen ion.

Evaluation of dissociation constants of weak electrolytes from conductance data by multiparametric curve-fitting

Summary A procedure is described for evaluating the thermodynamic dissociation constant of a weak electrolyte from conventional data on the concentration dependence of its equivalent conductance but without prior knowledge of its equivalent conductance at infinite dilution or of the concentration dependence of the equivalent conductance of any related strong electrolyte under the same conditions. The classical data of MacInnes and Shedlovsky for aqueous solutions of acetic acid are used to illustrate the procedure and to emphasize the constraints that should be imposed. It is concluded that statistical criteria for goodness of fit may usefully be supplemented by a demand for the most stable fit, and that the agreement between the conductometric and potentiometric values for the dissociation constant of acetic acid is very much better than has been believed.

Dissociation constant of acetic acid in N-methylpropionamide from 5 to 55�C and related thermodynamic quantities

The dissociation constant of acetic acid in N-methylpropionamide (NMP) has been determined at 11 temperatures from 5 to 55°C by measurement of the electromotive force of cells without liquid junction containing hydrogen gas electrodes and silver-silver chloride electrodes. The pK at 25°C was found to be 7.995 (molal scale) as compared with 4.756 in water; thus, acetic acid is much weaker in NMP than in water despite the higher dielectric constant of the nonaqueous solvent (176 as compared with 78.3 at 25°C). The standard changes of enthalpy and entropy for the dissociation of acetic acid were calculated from the temperature coefficient of pK, and thermodynamic functions for the transfer dissociation process were obtained. The weakness of acetic acid in NMP is discussed in terms of electrostatic effects and solute-solvent interactions.

Effect of the solution vapour pressure on the temperature dependence of the dissociation constant of acetic acid in water

The dissociation constant of acetic acid in water is between 4 and 26% greater at the solution vapour pressure than at one atmosphere in the range 250 to 374°C. K=ƒ(T)S.V.P. corresponds to neither the isobaric nor isochoric conditions, and the error introduced by neglecting the effect of the vapour pressure on the equilibrium at high temperatures is discussed.