Acid-base strengths

Acid-base status acidic amphoteric basic 

highly charged smaller cations are highly acidic. This point is illustrated for the series Na , Mg , Al , Si, P , S and in Table 2.3a. 

however, that Zn(OH)j is not classified as amphoteric as it should 

Cation Ionic potential ) Species Acidity-basicity 

Concerning the ultimate base, one might choose various small, highly charged, ions such as H-, F-, or 0 , all of which arc indeed quite basic. However, the electron appears to be the complement of the proton. It might be objected that the isolated electron has even less justification as a chemical entity than the proton, but solutions (and even solids) are known in which electrons are the anionic species And interestingly, solutions containing free electrons are very basic. This topic will be discussed in further detail in the section on liquid ammonia chemistry in the next chapter. 

The most fundamental measure of the inherent basicity of a species is the proton affinity. It is defined as the energy released for the reaction  

Note that the proton affinity (PA) has the opposite sign from the enthalpy of reaction of Eq. 9.47 Proton affinities are always listed as positive numbers despite referring to exothermic reactions (recall the same convention with electron affinities. Chapter 2). Proton affinities may be obtained in a number of ways. The simplest, and most fundamental for defining an absolute scale of proton affinities, is to use a Bom-Haber cycle of the sort  

The molecule BH must be sufficiently stable that its bond energy (enthalpy of atomization, A//A ) and ionization potential (1EBH) can be measured. Once several proton affinities have been established in this way, many more may be obtained by a technique known as ion cyclotron resonance spectroscopy and related methods,20 which measure the equilibrium concentrations of the species involved in the competition  

Since the proton affinity of a cation indicates its tendency to attract and hold a proton, its value will also be the enthalpy of dissociation of its conjugate acid in the gas phase. Consider HF (PAF- = 1554 kJ mol-1)  

Basicities affinity. It is defined as the energy released for the reaction  

The molecule BH must be sufficiently stable that its bond energy (enthalpy of atomization, and ionization potential (lEg ) can be measured. Once several 

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In the overview to this chapter we noted that the experimentally determined end point should coincide with the titration s equivalence point. For an acid-base titration, the equivalence point is characterized by a pH level that is a function of the acid-base strengths and concentrations of the analyte and titrant. The pH at the end point, however, may or may not correspond to the pH at the equivalence point. To understand the relationship between end points and equivalence points we must know how the pH changes during a titration. In this section we will learn how to construct titration curves for several important types of acid-base titrations. Our... 

To use the above expression for measuring the strength of an acid, a standard acid-base pair, say A2-B2, must be chosen, and it is usually convenient to refer acid-base strength to the solvent. In water the acid-base pair H30 + -H20 is taken as the standard. The equilibrium defining acids is therefore ... 

Flood, H., Forland, T. Roald, B. (1947). The acidic and basic properties of oxides. III. Relative acid-base strengths of some polyacids. Acta Chemica Scandinavica, 1, 790-8. 

Acid-base strength in MejSO The chemistry of MejSO (general) Coordination compounds of sulfoxides The chemistry of MejSO (inorganic)... 

Using the multisite complexation model (MUSIC), ° the surface of palladium oxide has been modeled providing useful data on the nature, number, and the acid-base strength of the hydroxyl groups present on the different faces (111) and (10 0) of... 

An inner-sphere complex is formed between Lewis acids and bases, while an outer-sphere complex involves a water molecule interposed between the acid and the base. A hard Lewis acid is a molecular unit of small size, high oxidation state, high electronegativity, and low polarizability whereas a soft Lewis acid is a molecular unit of relatively large size, characterized by low oxidation state, low electronegativity, and high polarizability. Based on this characterization, hard bases prefer to complex hard acids, and soft bases prefer to complex soft acids, under similar conditions of acid-base strength. 

Relationships of acid-base strengths are in fact relationships between free energies of reaction in terms of the thermodynamic... 

One of the fundamental questions in considerations of acid-base strengths in solution of molecules involving mesomerism is the rela-... 

In this chapter, a brief summary of studies that made use of calorimetry to characterize compounds comprising group IIIA elements (zeolites, nitrides, and oxides catalysts) was presented. It was demonstrated that adsorption microcalorimetry can be used as an efficient technique to characterize the acid-base strength of different types of materials and to provide information consistent with the catalytic data. 

It is important not to confuse acid/base strength, which depends on the degree of ionization, with concentration. Concentration measures how much acid or base is in... 

Acid—Base Strength Hardness and softness refer to special stability of hard-hard and soft-soft interactions... 

Chapter 9 Acid-Bose Chemistry 318 Acid-Base Concepts 318 Measures of Acid-Base Strength 330 Hard and Soft Acids and Bases 344... 

The aqueous solubility of the salt of a drug has also been considered a function of the acid-base strength and aqueous solubility of the counterion employed in the salt formation (Nelson, 1957). As an example, choline itself is considered strongly basic because of the hydroxide counterion,... 

This discussion should not be seen as explaining the acid/base character of oxides, i.e. their solubilities in water at various pH values. We are emphasising the close relationship between the acid/base behaviour of oxides and the nature of aqueous species. The dissolution of an oxide (other than a neutral oxide) in water, or in acids/alkalies, is an acid-base process, a chemical reaction rather than a mere separation of ions. The relative acid/base strengths of oxides are further discussed in Section 9.2. 

Water has a limiting effect on the strength of acids and bases. All strong acids behave the same in water 1—M solutions of the strong acids all behave as 1 M solutions of the HsO+ ion and very weak acids cannot act as acids in water. Acid-base reactions don t have to occur in water, however. When other solvents are used, the full range of acid-base strength shown in the table below can be observed. 

Acid/Base Strength of Conjugate Acid-Base Pairs... 

Acids and bases react to give salts and (usually) water. That is one definition of a salt. So, when we say salt solution, we are really talking about solutions that contain the conjugate acid or base of some other acid or base. The pH of a salt solution depends on the acid/base strength of the acid or base from which it was derived. There are three permutations on the problem salts of strong ac-ids/bases, salts of weak acids, and salts of weak bases. Let s consider them each in turn. 

Definition of Acids and Bases 222 Conjugate Acid-Base Pairs 222 Amphoteric Species 224 Strong Acids 225 Strong Bases 225 Weak Acids 226 Weak Bases 226 Polyprotic Acids 227 Acid and Base Strength Ka and Kb 228 Acid/Base Strength of Conjugate Acid-Base Pairs 230 Acid-Base Reactions 231... 

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