Acid dissociation constants and

A sample contains a weak acid analyte, HA, and a weak acid interferent, HB. The acid dissociation constants and partition coefficients for the weak acids are as follows Ra.HA = 1.0 X 10 Ra HB = 1.0 X f0 , RpjHA D,HB 500. (a) Calculate the extraction efficiency for HA and HB when 50.0 mF of sampk buffered to a pH of 7.0, is extracted with 50.0 mF of the organic solvent, (b) Which phase is enriched in the analyte (c) What are the recoveries for the analyte and interferent in this phase (d) What is the separation factor (e) A quantitative analysis is conducted on the contents of the phase enriched in analyte. What is the expected relative erroi if the selectivity coefficient, Rha.hb> is 0.500 and the initial ratio ofHB/HA was lO.O ... 

Acid Dissociation Constants and piC, Values for Some Weak Electrolyt (at 25°C) es... 

The Henderson-Hasselbalch equation provides a general solution to the quantitative treatment of acid-base equilibria in biological systems. Table 2.4 gives the acid dissociation constants and values for some weak electrolytes of biochemical interest. 

Bacarella, A. L. Grunwald, E. Marshall, H. R Purlee, E. L., The potentiometric measurement of acid dissociation constants and pH in the system methanol-water. pKa values for carboxylic acids and anilinium ions, j. Org. Chem. 20, 747-762 (1955). 

Fig. 10. The formulae of some of the bases in DNA and RNA. The acid dissociation constants and the methylmercury constants and binding centres axe shown (after R. B. Simpson)...

D. Behar, G. Czapski, J. Rabani, L.M. Dorfman, and H.A. Schwarz, Acid dissociation constant and decay kinetics of the perhydroxyl radical. J. Phys. Chem. 74, 3209-3213 (1970). 

The equilibrium constant for the isotope-exchange equilibrium can be expressed (6) in terms of the solvent isotope effects on the acid-dissociation constants and of the monocarboxylic acid and dicarboxylic acid monoanion, respectively. It follows that a lower value for the fractionation factor of the hydrogen-bonded proton means that the solvent isotope effect on the acid-dissociation constant will be lower for the dicarboxylic acid monoanion than for the monocarboxylic acid. 

The earliest LFER, advanced by Bronsted, correlates the acid dissociation constant and base strength (1/A h) of species with its effectiveness as a catalyst in general acid (At h) and base (Atgl-catalyzed reactions respectively. The relationships take the form... 

Ezumi, K. and Kubota, T. Simultaneous determination of acid dissociation constants and true partition coefficients by analyses of the apparent partition coefficient, Chem. Pharm. Bull, 28(1) 85-91, 1980. 

X10 . The molarity in this problem tells you that the concentration of benzoic acid is 5.0 X10 . You also know that the concentration of benzoic acid s conjugate base is the Scime as the given H+ concentration. All that remains is to write an equation for the acid dissociation constant and plug in these concentrations. 

Acid Dissociation Constants and Formation Constants. Attempts to determine acid dissociation constants of bisacetylacetoneethylenediimine and bis-acetylacetone-m-phenylenediamine in 50 volume % dioxane-water were unsuccessful. The procedure used was successful when applied to bis (/ -diketones) (II). Likewise, attempts to determine formation constants of the tetradentate / -keto-imines were unsuccessful, apparently because of hydrolysis. 

Comparison of these new compounds with the common xanthene dyes reveals that substitution of H at C-9 has only a minor influence in the absorption and emission spectra. Table 15 summarizes the spectral properties of HF, TBHF, and TIHF as well as the acid dissociation constants and electrochemical potentials. The color, fluorescence quantum yield, ap-... 

It is also common to measure by voltammetry the thermodynamic properties of purely chemical reactions that are in some way coupled to the electron transfer step. Examples include the determination of solubility products, acid dissociation constants, and metal-ligand complex formation constants for cases in which precipitation, proton transfer, and complexation reactions affect the measured formal potential. Also in these instances, studies at variable temperature will afford the thermodynamic parameters of these coupled chemical reactions. 

For catalytic waves of hydrogen evolution in ammoniacal cobalt solutions, it has been observed (132) that ery/Aro-phenylcysteine gives a higher catalytic wave than the threo form (Fig. 28). These differences can be explained partly by differences in acid dissociation constants, and partly by variations in the stability constants of the cobalt-phenyl-cysteine complexes. 

Bauer G (2000) Reactive oxygen and nitrogen species efficient, selective and interactive signals during intercellular induction of apoptosis. Anticancer Res 20 4115-4140 Beckwith AU, Davies AG, Davison IGE, Maccoll A, Mruzek MH (1989) The mechanisms of the rearrangements of allylic hydroperoxides 5a-hydroperoxy-3p-hydrocholest-6-ene and 7a-hydro-peroxy-3(1-hydroxycholest-5-ene. J Chem Soc Perkin Trans 2 815-824 Behar D, Czapski G, Rabani J, Dorfman LM, Schwarz HA (1970) The acid dissociation constant and decay kinetics of the perhydroxyl radical. J Phys Chem 74 3209-3213 Benjan EV, Font-Sanchis E, Scaiano JC (2001) Lactone-derived carbon-centered radicals formation and reactivity with oxygen. Org Lett 3 4059-4062 Bennett JE, Summers R (1974) Product studies of the mutual termination reactions of sec- alkylper-oxy radicals Evidence for non-cyclic termination. Can J Chem 52 1377-1379 Bennett JE, Brown DM, Mile B (1970) Studies by electron spin resonance of the reactions of alkyl-peroxy radicals, part 2. Equilibrium between alkylperoxy radicals and tetroxide molecules. Trans Faraday Soc 66 397-405... 

Acid Dissociation Constants and Dissociation Constants of Complex Ions... 

In using acid dissociation constants and the dissociation constants of complex ions, it is convenient to take the base 10 logarithms of equations 1.2-7 and 1.2-9 to obtain... 

Acid dissociation constants and dissociation constants of complex ions determine the concentrations of species that are present in a solution at equilibrium under specified conditions. Ionic dissociation reactions occur rapidly and tend to remain at equilibrium during an enzyme-catalyzed reaction. Since ATP (see Fig. 1.1) is the primary carrier of energy in biochemical systems and since a good deal is known about its binding properties, these properties are considered here in some detail. 

In this chapter we have seen that acid dissociation constants are needed to calculate the dependence of apparent equilibrium constants on pH. In Chapter 3 we will discuss the calculation of the effects of ionic strength and temperature on acid dissociation constants. The database described later can be used to calculate pKs of reactants at 298.15 K at desired ionic strengths. Because of the importance of pKs of weak acids, Table 1.3 is provided here. More experimental measurements of acid dissociation constants and dissociation constants of complex ions with metal ions are needed because they are essential for the interpretation of experimental equilibrium constants and heats of reactions. A major database of acid dissociation constants and dissociation constants of metal ion complexes is provided by Martell, Smith, and Motekaitis (2001). 

As mentioned at the end of Chapter 1, an understanding of heterolytic reaction mechanisms must be accompanied by an understanding of the properties of organic acids and bases. Through this understanding, an ability to predict the reactive species in organic reactions and the reactive sites in organic molecules will evolve. Therefore, this chapter focuses on the properties of acids, dissociation constants, and the relative acidities observed for protons in different environments. 

This is a simplified version of the more general expression in Chapter 3. The influence of [OH ] and [H ] on the TA is small and can often be ignored. The borate contributes about 3% of the TA, and if not determined independently, can be estimated from the apparent boric acid dissociation constants and the salinity, relying upon the relative constancy of composition of sea salt. This correction would give the carbonate alkalinity (CA) CA = [HCO3 ] + 2[C03 ]... 

Although the side-chain groups R, R, R have only a weak influence on the acid dissociation constants and the reverse situation, namely a change in polarity due to an ionization event in the vicinity of R, R, R, can have a significant influence on retention. The capacity factor equation describing the sorption to a reversed phase of the above simple nonpolar peptide as a function of pH is given by... 

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). 

The results which were obtained for the acid dissociation constants and the formation constants for the rare earth chelates are given in Table II along with the log Ki values for the ligands which were studied earlier. We have included the measured values for some other ions which were... 

In this particular case, Ke is an acid dissociation constant and would be indicated as... 

The perturbation of the acid dissociation constant of an amino acid residue as a consequence of its environment within a protein represents another mechanism for enhancing its reactivity relative to a free amino acid in solution. Most amino acid residues react with their respective modification reagents in their unprotonated form instead of in their conjugate acid form. Eq. (4.10) describes the pH dependence of the simple bimolecular reaction (eq. 4.9) of the free base form of nucleophilic amino acid side chain with a non-ionizable modification reagent where is the acid dissociation constant and Aj is the total concentration of amino acid. 

The synthesis of several thioether pentadentate ligands (95) is described.149 Acid dissociation constants and metal-chelate formation for a series of divalent metals, as well as formation constants for dioxygen adducts of their cobaltous complexes, are also reported. 

That is, the acid dissociation constant and the base dissociation constant are related through the ionic product of water. 

The Gran plot is an alternative method for locating the end point in a titration. In this method, a linear plot is produced that can reveal both the acid dissociation constant and the volume of base required to reach the end point. Unlike the normal titration curve and derivative curves, which find the end point only from data located in the end point region, the Gran plot uses data far away from the end point. This can decrease the tedium of taking many measurements after dispensing very small volumes of titrant in the end point region. 

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