Acid , generally dissociation

There are a considerable number of stable crystalline salts of the ammonium ion [14798-03-9] NH. Several are of commercial importance because of large scale consumption in fertiliser and industrial markets. The ammonium ion is about the same size as the potassium and mbidium ions, so these salts are often isomorphous and have similar solubiUty in water. Compounds in which the ammonium ion is combined with a large, uninegative anion are usually the most stable. Ammonium salts containing a small, highly charged anion generally dissociate easily into ammonia (qv) and the free acid (1). At about 300°C most simple ammonium salts volatilize with dissociation, for example... 

Decomposition and Detonation Hazard. Ammonium nitrate is considered a very stable salt, even though ammonium salts of strong acids generally lose ammonia and become slightly acidic on storage. For ammonium nitrate, endothermic dissociation from lowering pH occurs above 169°C. 

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 ... 

The macrocycles are generally characterized by their extreme resistance to dissociation, (see however Prob. 6). The kinetics of acid-promoted dissociation of an extensive series of Ni(II) and Cu(II) complexes, (ML) have been reported,The general rate law is (see Prob. 2, Chap. 2) ... 

The next issue that arises from the weak acidity of carbon acids involves the degree of self-dissociation. In Eq. 3, the equihbrium constant is determined by measuring the concentration of the four species in the equation, but this requires that the carbon acid self-dissociates to an extent that a measurable quantity of the carbanion is formed. Again, because carbon acids are generally weak, this requirement often is not met and therefore another type of equilibrium measurement... 

Carbonic acid, H2CO3, is a weak acid that dissociates by the above reaction (B). In general, a solution of a weak acid HA that dissociates into H and A will serves as a buffer solution. Thus, respiration in lungs contributes to physiological buffer actions. 

The normal value of pH of the extracellular fluids at 37 °C is about 7.4, while that of the intracellular fluids is about 7.2. This can be explained by the buffering action of carbonic acid. In general, when a weak acid HA dissociates into IH and A , the following relationship holds ... 

The rates of dissociation of Gd3+ chelates used or proposed as CAs are generally low at pH = 7.4. The complexes dissociate much faster in acidic solutions, when the proton-assisted dissociation predominates. In order to compare the kinetic stabilities of complexes, some authors suggest use of the first-order rate constants (kobs) obtained in 0.1 M HCl or HC104 solution. Wedeking et al. compared the acid-assisted dissociation rates (kobs) of several acyclic and cyclic Gd3+ complexes with the long term (14 days) deposition of Gd in the whole body of mice [ 15]. They found an inverse proportionality between the dissociation rates (kobs) and the total residual Gd, i.e. the lower the dissociation rate, the less the residual Gd found in the bodies of the mice [15]. The (kobs) values determined by Wedeking et al. and other authors for several Gd3+ and Y3+ complexes are shown in Table 1. 

Tables 4 and 5 include several electron adducts of aromatic and olefinic carboxylic acids. The dissociation constants of these radicals are generally much higher than those of the parent acids because of the additional charge. It appears that one should not compare the value of 12-0 for the electron adduct (C6H5C02H) with pK = 4-2 for C6HsC02H. Instead, a comparison of the first pA = 5 3 for the conjugate acid of the electron adduct (C6HsC02H2)" seems more suitable. Similarly pK for the conjugate acid of the electron adduct of the C6HsC(OH)OCH3 (5-5) is comparable to that of the acid or...

A. The use of indicators and indicator test papers An indicator is a substance which varies in colour according to the hydrogen-ion concentration. It is generally a weak organic acid or weak base employed in a very dilute solution. The undissociated indicator acid or base has a different colour to the dissociated product. In the case of an indicator acid, Hind, dissociation takes place according to the equilibrium... 

Substituents in the ortho positions of aromatic acids generally retard esterification. Such sterically hindered acids may be esterified by dissolving in 100% sulfuric acid and pouring the solutions into the desired alcohol. This reaction is limited to those acids which dissociate in sulfuric acid to give a positive acyl ion, RCO (cf. method 314). 

T ivalent and ammonium forms of Y zeolite possess catalytic activities for many acid-catalyzed reactions 11, 12, 16, 19). Although it is generally accepted that acidic hydroxyl groups are responsible for the activity of the calcined ammonium form 4, 6,19, 24), the reasons for the activity of the cation forms have been less well elucidated 6, 7, 9,15,19, 20, 25). Since the catalytic activity of the divalent cation forms usually is exhibited when suflBcient cations have been introduced so as to occupy accessible positions in the lattice, it has been suggested that various properties of the cations may be responsible for the introduction of active sites. Properties of the cations such as their electrostatic field and surface diffusion have been suggested 12, 15). Alternatively, it has been suggested that the divalent cations can introduce Bronsted acidity by dissociation of water 3, 5, 6,18,19, 20), thus... 

Firstly, ion exchange resins when hydrated generally dissociate to yield equivalent amounts of oppositely charged ions. Secondly, as with conventional aqueous acid or alkali solutions, resins in their acid or base forms may be neutralized to give the appropriate salt form. Finally, the degree of dissociation can be expressed in the form of an apparent equilibrium constant (or pK value) which defines the electrolyte strength of the exchanger and is usually derived from a theoretical treatment of pH titration curves. ... 

The concepts and equations of acid-base dissociation have referred chiefly to aqueous solutions. Recently, interest in the behavior of acids and bases in solvents other than water has increased considerably. The classical definition of an acid and a base, which is satisfactory for water solutions, is too limited for other solvents. Because of the great importance of the general question of the acid-base equilibrium, the clear and fruitful views of Bronsted are exhaustively considered in a special (fourth) chapter. ... 

The ionization of citric acid moieties may be described by the general dissociation reaction... 

We can now write some general rules for solving chemical equilibrium problems, using the approximation approach. These rules should be applicable to acid-base dissociation, complex formation, oxidation-reduction reactions, and others. That is, all equilibria can be treated similarly. 

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