Weak acids/bases

In contrast to these trends observed for the stibine adducts, the H-NMR spectra of the bismuthine adducts R3M—BiR without exception show almost the same chemical shifts due to the organic groups as the starting trialkylalanes, -gallanes and -bismuthines, again indicating very weak acid-base interactions in solution. 

C17-0037. Outline the procedure for working an equilibrium problem for a weak acid-base system. 

Strong acids completely dissociate (ionize) in water. Weak acids partially dissociate and establish an equilibrium system. There is a large range of weak acids based upon their ability to donate protons. Consider the general weak acid HA and its reaction when placed in water ... 

Our goal in this chapter is to help you continue learning about acid-base equilibrium systems and, in particular, buffers and titrations. If you are a little unsure about equilibria and especially weak acid-base equilibria, review Chapters 14 and 15. You will also learn to apply the basic concepts of equilibria to solubility and complex ions. Two things to remember (1) The basic concepts of equilibria apply to all the various types of equilibria, and (2) Practice, Practice, Practice. 

Strong acids and bases (and strong electrolytes) dissociate completely in water. Therefore, you can use the concentrations of these compounds to determine the concentrations of the ions they form in aqueous solutions. You cannot, however, use the concentrations of weak acids, bases, and electrolytes in the same way. Their solutions contain some particles that have not dissociated into ions. Nevertheless, important changes in [HsOT and [OH ] take place because dissolved ions affect the dissociation of water. 

Given that AH = —254.4 kJ mol-1 and S° = 14.81 J K-1 mol-1 for hexagonal solid boron nitride, use the data of Appendix C to calculate the free energy change for the hydrolysis of one mole of BN (s) by liquid water at 25 °C. Ignore the weak acid-base interaction of the products and the very slight solubility of B(OH)3(s). 

WABN-SC weak acids, bases, and neutrals isolated at pH 8.0 on XAD-4 resin (weak phenols, anilines, and a wide variety of neutral compounds). 

T. M. Tesfai, Unified Approximations A New Approach for Monoprotic Weak Acid-Base Equilibria, J. Chem. Ed. 2004, 81, 1367. 

The most effective buffering system contains equal concentrations of the acid, HA, and its conjugate base, A-. According to the Henderson-Hasselbalch equation (2.6), when [A-] is equal to [HA], pH equals pKa. Therefore, the pKa of a weak acid-base system represents the center of the buffering region. The effective range of a buffer system is generally two pH units, centered at the pKa value (Equation 2.9). 

The acid-base chemistry we will encounter occurs in aqueous media. Water itself has some very weak acid-base properties, and therefore sets some limits on the... 

Weak acid-base chiral complex formation represents hydrogen bond catalysis (see Chapter 9) and deprotonation followed by cation/anion association under homogeneous, and also under phase-transfer conditions (see Chapter 4) [14, 65],... 

In the same manner as described in Section 2.2.5, mathematical expressions for the buffer capacity of polyprotic weak acid/base systems can be developed. When one adds a strong base such as NaOH to an aqueous buffer solution containing a polyprotic weak acid (HnA), the electroneutrality would be ... 

At the second critical pH (pH,, ), which is usually below the protein isoelectric point, strong electrostatic interaction between positively charged protein molecules and anionic polysaccharide chains will cause soluble protein/polysaccharide complexes to aggregate into insoluble protein/polysaccharide complexes. For negatively charged weak acid-based (e.g., carboxylic acid) polysaccharides like pectin, with the decrease of pH below the pKa of the polysaccharide, protein (e.g., bovine serum albumin (BSA))/polysaccharide (e.g., pectin) insoluble complexes may dissociate into soluble complexes, or even non-interacted protein molecules and polysaccharide chains, due to the low charges of polysaccharide chains as well as the repulsion between the positively charged proteins (Dickinson 1998). 

Use of statistical copolymers in blends is usually predicated on the existence of a specific interaction between one of the comonomers in the copolymer and other ingredients in the mixture. Thus PVC is miscible with the ethyicne/ethyl acrylate/carbon monoxide copolymers [28]. The homogenizing effect here is a weak acid-base interaction between the carbonyl of the copolymer and the weakly... 

Similar to the log D-pH profile, the distribution of the compounds in a chromatographic partition system is also influenced by the pH. Charged species have much shorter retention times than their uncharged parent compounds. Horvath et al. [105 described first the effect of solute ionisation on the retention of weak acids, bases and ampholytes on octadecyl silica, both theoretically and experimentally. They have found a similar equation to Eqs. (12.11) and (12.12) that describes the pH dependence of the isocratic retention factor (A) for weak acids as shown in Eq. (12.1.3) ... 

Chan CC and Lee CJ. A mass transfer model for the extraction of weak acids/bases in emulsion liquid-membrane systems. Chem Eng Sci 1987 42 83-95. 

Sections 15.4 and 15.5 outline methods for calculating equilibria involving weak acids, bases, and buffer solutions. There we assume that the amount of hydronium ion (or hydroxide ion) resulting from the ionization of water can be neglected in comparison with that produced by the ionization of dissolved acids or bases. In this section, we replace that approximation by a treatment of acid-base equilibria that is exact, within the limits of the mass-action law. This approach leads to somewhat more complicated equations, but it serves several purposes. It has great practical importance in cases in which the previous approximations no longer hold, such as very weak acids or bases or very dilute solutions. It includes as special cases the various aspects of acid-base equilibrium considered earlier. Finally, it provides a foundation for treating amphoteric equilibrium later in this section. 

Both strong-acid cation and strong-base anion resins are high ionized in water thus, they can work in the entire pH range. The pH does not affect the ion-exchange performances. Conversely, weak-acid cation and weak-base anion resins are more like weak acid (base). For example, their ionization strongly depends on pH. When pH is below 6.0, weak-acid cation resin s performance will be significantly decreased. Similar phenomenon will occur to weak-base anion resin at pH above 7.0. 

Use the search engine Google to locate the Web document The Fall of the Proton Why Acids React with Bases by Stephen Lower. This document explains acid/base behavior in terms of the concept of proton free energy. How is an acid/base titration described in this view In a titration of strong acid with strong base, what is the free energy sink In a complex mixture of weak acid/base systems, such as serum, what happens to protons ... 

Pudipeddi M, Serajuddin ATM, Grant DJW, and Stahl PH. Solubility and Dissolution of Weak Acids, Bases, and Salts. In Stahl PH and Wermuth CG. Handbook of Pharmaceutical Salts. Wiley-VCH, Weinheim, Germany, 2002, pp. 19-39. 

Bhowal, A. and Datta, S. (1998). A mathematical model for the analysis of extraction data of weak acids/bases in hquid surfactant membranes. J. Membr. Sci., 139, 103-8. 

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