Acid-base reactions salt formation

Effects of Additives. Selected additives to molten nitrate systems offer possibilities of specific acid-base reactions or formation of specific complexes with the various chemical species. Acids and bases are conveniently denoted in oxyanionic molten salt systems by the Lux-Flood definition (18, 19). Acids are defined as compounds capable of removing oxide ions from the melt, while bases are defined as compounds capable of donating oxide ions to the melt. Examples of various acidic and basic species may be found in the general review articles (14, 15,... 

The observed complexity of the Se(IV) electrochemistry due to adsorption layers, formation of surface compounds, coupled chemical reactions, lack of electroactivity of reduction products, and other interrelated factors has been discussed extensively. Zuman and Somer [31] have provided a thorough literature-based review with almost 170 references on the complex polarographic and voltammetric behavior of Se(-i-IV) (selenous acid), including the acid-base properties, salt and complex formation, chemical reduction and reaction with organic and inorganic... 

This concept covers most situations in the theory of AB cements. Cements based on aqueous solutions of phosphoric acid and poly(acrylic acid), and non-aqueous cements based on eugenol, alike fall within this definition. However, the theory does not, unfortunately, recognize salt formation as a criterion of an acid-base reaction, and the matrices of AB cements are conveniently described as salts. It is also uncertain whether it covers the metal oxide/metal halide or sulphate cements. Bare cations are not recognized as acids in the Bronsted-Lowry theory, but hydrated... 

A base has the ability to donate a pair of electrons and an acid the ability to accept a pair of electrons to form a covalent bond. The product of a Lewis acid-base reaction may be called an adduct, a coordination compound or a coordination complex (Vander Werf, 1961). Neither salt nor conjugate acid-base formation is a requirement. 

The Usanovich theory is the most general of all acid-base theories. According to Usanovich (1939) any process leading to the formation of a salt is an acid-base reaction. The so-called positive-negative definition of Usanovich runs as follows. 

The senior author first became interested in acid-base cements in 1964 when he undertook to examine the deficiencies of the dental silicate cement with a view to improving performance. At that time there was much concern by both dental surgeon and patient at the failure of this aesthetic material which was used to restore front teeth. Indeed, at the time, one correspondent commenting on this problem to a newspaper remarked that although mankind had solved the problem of nuclear energy the same could not be said of the restoration of front teeth. At the time it was supposed that the dental silicate cement was, as its name implied, a silicate cement which set by the formation of silica gel. Structural studies at the Laboratory of the Government Chemist (LGC) soon proved that this view was incorrect and that the cement set by formation of an amorphous aluminium phosphate salt. Thus we became aware of and intrigued by a class of materials that set by an acid-base reaction. It appeared that there was endless scope for the formulation of novel materials based on this concept. And so it proved. 

The Arrhenius concept was of basic importance because it permitted quantitative treatment of a number of acid-base processes in aqueous solutions, i.e. the behaviour of acids, bases, their salts and mixtures of these substances in aqueous solutions. Nonetheless, when more experimental material was collected, particularly on reaction rates of acid-base catalysed processes, an increasing number of facts was found that was not clearly interpretable on the basis of the Arrhenius theory (e.g. in anhydrous acetone NH3 reacts with acids in the absence of OH- and without the formation of water). It gradually became clear that a more general theory was needed. Such a theory was developed in 1923 by J. N. Br0nsted and, independently, by T. M. Lowry. 

S. A. Arrhenius defined an acid as any hydrogen-containing species able to release protons and a base as any species able to form hydroxide ions [71]. The aqueous acid-base reaction is the reaction between hydrogen ions and hydroxide ions with water formation. The ions accompanying the hydrogen and hydroxide ions form a salt, so the overall Arrhenius acid-base reaction can be written ... 

Whenever possible, the chemical reactions involved in the formation of diastereomers and their conversion to separate enantiomers are simple acid-base reactions. For example, naturally occurring (S)-(-)-malic acid is often used to resolve amines. One such amine that has been resolved in this way is 1-phenylethylamine. Amines are bases, and malic acid is an acid. Proton transfer from (S)-(-)-malic acid to a racemic mixture of (/ )- and (5)-1-phenylethylamine gives a mixture of diastereomeric salts. 

Quaternary ammonium salts of dantrolene and clodanolene have been prepared, and the effect of the organic cation on the aqueous solubility has been reported (Ellis et al., 1980). It was reasoned that since the hydantoin moiety in each drug is weakly acidic, a strong base should be found for salt formation. The 13 different quaternary ammonium compounds were therefore used in the hydroxide salt form. The acid-base reaction proceeded rapidly, and the salt products were stable during recrystallization steps. Of the four salts for clodanolene, the aqueous solubilities ranged from 2- to 100-fold that of clodanolene sodium, on a mass basis. Of the 11 salts for dantrolene, the benzyl-trimethyl ammonium salt exhibited comparable solubility to that of dantrolene sodium. Among the other 10 salts were several examples that yielded enhanced solubilities of up to 1000-fold that of the sodium salt. Twelve of the Lfteen salts successfully demonstrated muscle relaxant activity when administered orally. 

The bonding to form the imidazole ring would suggest that reduction with complex metal hydrides should be possible. Lithium aluminum hydride, however, would be expected to undergo an acid-base reaction with the N—H of the 1-position forming the anion of imidazole which would resist further attack by complex hydride ions. Such observations were made by Bohlmann97 with benzimidazole (131). Thus at room temperature or below only salt formation was observed on reaction of lithium aluminum hydride with benzimidazole... 

The synthesis of amides directly from carboxylic acids is not easy because the reaction of an amine with a carboxylic acid is a typical acid-base reaction resulting in the formation of a salt (Following fig.). Some salts can be converted to an amide by heating strongly to expel water. 

The above discussion indicates that acidic phosphate salts may play an important role in forming CBPCs. To use acid phosphates as the acidic components in acid-base reactions, primary requirement is solubility in water. Table 4.1 lists solubilities of some of the common hydrogen phosphates that are available in the literature and are useful intermediate phases during formation of CBCs. 

Much important chemistry, including most of the chemistry of the natural world, occurs in aqueous solution. We have already introduced one very significant class of aqueous equilibria, acid-base reactions. In this chapter we consider more applications of acid-base chemistry and introduce two additional types of aqueous equilibria, those involving the solubility of salts and the formation of complex ions. 

Factors influencing the rate of chemical reaction are surface tension polarity of the organic solvent acid-base properties of the aqueous phase relative rate of hydrolysis and other side reactions (salt formation, etc.) rate of separation of polymer out of solution rate of removal of side products of the reaction. 

However, the case in which the solubility of a solid can be calculated from the known analytical concentration of added components and from the solubility product alone is very seldom encountered. Ions that have dissolved from a crystalline lattice frequently undergo chemical reactions in solution, and therefore other equilibria in addition to the solubility product have to be considered. The reaction of the salt cation or anion with water to undergo acid-base reactions is very common. Furthermore, complex formation of salt cation and salt anion with each other and with one of the constituents of the solution has to be considered. For example, the solubility of FeS(s) in a sulfide-containing aqueous solution depends on, in addition to the solubility equilibrium, acid-base equilibria of the cation (e.g., Fe + H2O = FeOH + H ) and of the anion (e.g., S + HjO = HS + OH, and HS" + H2O = H2S + OH ), as well as on equilibria describing complex formation (e.g., formation of FeHS" or FeSi ). 

When Fe " salts are dissolved in water, the solution becomes acidic due to formation of Fe(H20)50H and H30 . The overall process involves both Lewis and Br0nsted-Lowry acid-base reactions. Write the equations for the process. 

A particular and very interesting chapter in the chemistry of the QBA is devoted to their free bases. The term free base has been universally adopted for the product with basic properties which is formed upon alkalization of an alkaloid salt and which reverts to the original salt in acidic solutions. Thus, the formation of a free base is a reversible acid-base reaction. Generally, a free base can be considered as a kind of artifact because it does not occur in (acidic) plant tissues. The natural form of a QBA is the iminium salt as can be illustrated by the typically bright colours of the organs, fresh latex or alcoholic extracts of plants. 

What is a salt How are salts formed by acid-base reactions Write chemical equations showing the formation of three different salts. What other product is formed when an aqueous acid reacts with an aqueous base Write the net ionic equation for the formation of this substance. 

One method used for the preparation of [Pt(en)2]Cl2 or [Pt(en)3]Cl4 is the direct reaction between ethylenediamine and PtCU or PtCLt, respectively. The technique is to add slowly the solid platinum salts to the liquid ethylenediamine. This addition is accompanied by a vigorous evolution of heat, which is to be expected whenever a strong acid is added to a strong base. Recall (Section 2.1) that in terms of the Lewis definition of acids and bases, the formation of coordination compounds involves an acid-base reaction. In this particular case, the platinum ions are the acids and ethylenediamine is the base. Metal dimethylsulfoxide complexes have been prepared and characterized. One method used to prepare some of these complexes is a direct reaction (12) in the absence of any added solvent. 

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