Acidity operational definition

Returning to our two definitions of an acid, the first, the operational definition, gives clearcut instructions on how to decide whether a given substance is an acid. Dissolve it in water and see if it has certain properties. The second (conceptual) definition, however, has the deeper significance since it includes our knowledge of why an acid has these particular properties. It provides a basis for finding hidden likenesses between acid-base reactions in water and other reactions in other solvents. Each type of definition has its merit neither is the definition. 

A qualitative listing of the hardness of some acids and bases is given in Table 8.3. The treatment has also been made quantitative, with the following operational definition ... 

The sizes of the prion domains vary from 70 amino acid residues (HET-s) to 250 amino acid residues (Rnqlp) (Fig. 1), but their borders are not precisely defined by functional criteria since these domains may be subjected to sizeable truncations while retaining their prionogenic properties (Edskes and Wickner, 2002 Ross et al., 2005). Nor are they precisely defined by the extent of N/Q-rich tracts since not all prion domains have them and the preponderance of these residues can vary within a given prion domain. Since the functional domains tend to have globular folds (Section II.B), an operational definition of a prion domain may be that it terminates with the last (or first) residue that is not part of the functional domain, although this definition is applicable only when that fold is known. 

Operational Definition of Lipids How is the definition of lipid different from the types of definitions used for other biomolecules that we have considered, such as amino acids, nucleic acids, and proteins ... 

Originally, the caseins were defined as those phosphoproteins which precipitate from raw skim milk upon acidification to pH 4.6 at 20°C, and the individual families were identified by alkaline urea gel electrophoresis (Whitney et al 1976). With the resolution of their primary structure, it became possible to classify them according to their chemical structure, rather than on the basis of an operational definition. When one does this, it is apparent that not all of the caseins contain phosphorus (Table 3.1) some are also found in the acid whey after removal of the precipitated caseins. 

Humic and fulvic acids (HA and FA, respectively) are differentiated on the basis of operational definitions Both fractions include not only the aromatic components but also a variety of plant components. Thus, in reality, HA and FA are extremely heterogeneous fractions. 

Various separation methods have been used to isolate, fractionate, and characterize humic materials. Originally it was fractionation, based on solubility differences of humic components in diluted alkalis and acids, which laid the ground work for the first classifications of humic substances (HS) in the 19th century (Mulder, 1861 Sprengel, 1837) and provided for operational definition of HS (Kononova, 1966). And now, alkali extraction is the method of choice for isolating HS from solid humus-containing substrates like soil, peat, coal, and so on (Swift, 1996), while hydrophobic resins (e.g., Amberlite XAD resins) are typically used to extract HS dissolved in natural waters (Aiken, 1985). Initial research on HS began with the used simple separation methods to prove, examine, and define characteristics of components of humic matter (Oden, 1919).Today, however, advances in HS research require ever more sophisticated techniques of separation combined with structural analysis (Orlov, 1990 Stevenson, 1994). 

Naming Acids and Bases Operational Definitions of Acids and Bases Conceptual Definition of Acids and Bases Arrhenius Acids and Bases... 

The extent to which a given reaction responds to electronic perturbation constitutes a measure of the electronic demands of that reaction, which is determined by its mecha-, nism. The introduction of substituent groups into the framework and the subsequent alteration of reaction rates helps delineate the overall mechanism of reaction. Early work examining the electronic role of substituents on rate constants was first tackled by Burckhardt and firmly established by Hammett (13, 14, 77, 78). Hammett employed, as a model reaction, the ionization in water of substituted benzoic acids and determined their equilibrium constants K. See Equation 1.28. This led to an operational definition of o-, the substituent constant. It is a measure of the size of the electronic effect for a given substituent and represents a measure of electronic charge distribution in the benzene nucleus. 

Their unique relation to water systems favors the inclusion of acid-base reactions in deuterium oxide with aqueous acid-base equilibria, even though some aspects of the chemistry suggest inclusion with nonaqueous solvents. In studies such as those of deuterium isotope effects, it is desirable to be able to measure pD as an index of acidity in heavy water. Glass electrodes respond in a nemstian way to changes in deuterium ion concentration, and therefore the usual combination of glass and calomel electrodes can form the basis of an operational definition of pD ... 

Aqueous speciation. The distribution of dissolved components among free ions, ion pairs, and complexes. For example, dissolved iron in acid mine drainage (AMD) can be present as Fe( q) (free ferrous iron), FeS04(aq> (ion pair), Fef q) (free ferric iron), Fe(OH)(j q), and FeS04(aq) species. These species are present in a single phase, aqueous solution. Aqueous speciation is not uniquely defined but depends on the theoretical formulation of mass action equilibria and activity coefficients, i.e. it is model dependent. Some aqueous speciation can be determined analytically but operational definitions and assumptions are still unavoidable. 

Researchers have devised numerous extraction and fractionation schemes to deal with the heterogeneous nature of humic substances. Traditionally, the operational definition of humic substances as used by the International Humic Substances Society (Hayes et al., 1989) is based on the solubility in a series of acids and bases. In this scheme, humic substances are classified into three chemical groupings (1) fulvic acid, soluble in both alkali and acid solutions, has the lowest molecular weight and is generally considered the most susceptible to microbial degradation (2) humic acid, soluble in alkali but not in acid, is intermediate in molecular weight and decomposability and (3) humin, insoluble in both alkali and acid solutions, is the most... 

Any acid-base system of unknown distribution can be characterized fiilly with the help of two parameters. For example, in a solution of phosphates (Na salts), the equilibrium composition with regard to the six species (H3PO4, H2P0,T, HP04 , P04, H, and OH ) can be resolved completely if the concentration of at least two of the species or two of certain combinations thereof are evaluated analytically capacity factors such as [ANC] and [BNC] are especially valuable for defining acid-base systems in terms of conservative parameters. They can be determined frequently with ease and relatively good accuracy thus the discrepancy between conceptual and operational definition is very small. 

It should be emphasized that the strength of the operational definition of pH is that it provides a coherent scale for the determination of acidity or alkalinity. Measured pH values cannot be expected to yield a detailed picture of solution composition that is entirely consistent with solution theory, however. This uncertainty stems from our fundamental inability to measure single-ion activities. That is, the operational definition of pH does not yield the exact pH as defined by the equation... 

The classical definition of fulvic acids is not very specific. Many biochemical substances such as proteins, sugars, and fatty acids would fall under this classification. These substances, in many instances, can hardly be considered "humic" in nature. But, if one uses the classical definition of fulvic acids these substances are included. No doubt the observations made above that polysaccharidelike substances constitute the major components of sedimentary fulvic acids is partly attributable to the fact that the operational definition classes polyuronides as fulvic acids. It is not the intent of this paper to discuss the merits of using the classical operational definition for fulvic acids as opposed to one s perception of what true fulvic acids are. He know far too little about the composition of humic isolates and about their origin to begin discussions of whether they are humified or not. He therefore chose to use operational definition with recognition that well defined structural entities can sometimes be a part of what is isolated. 

Unfortunately this equation is as quantitative as HSAB gets. There was no exact definition of hardness, ry, and no operational definition which allowed it to be measured. The values in Tables 1.4 and 1.5 are useful only in ordering acids and bases. They are not transferable as numbers to any other examples. Therefore applications have always been qualitative. Even so, the HSAB concept has been extremely useful in correlating and understanding a great deal of experimental data. 

Most acids tend to be reactive substances. Test the reactivities of three acids with several common substances, and develop an operational definition for acidic solutions. 

Smnmarize the reactions of the three acids with the substances you tested. This summary constitutes an operational definition of an acid. 

The really serious objection to the HSAB concept was that no exact definition of hardness or softness was given. There was an operational definition as given by Ahrland, Chatt and Davies, but it only put Lewis acids into one of two boxes. There was no way to rank-order within the boxes, though there were borderline cases. There was a rank-ordering of bases, given by (2), but it was only approximate and did not distinguish between all the bases with the same donor atom. Finally all that was done was to put bases into one of the two boxes labelled hard and soft. 

An operational definition could be given using the equilibrium constant or reaction heat, for a reaction such as (3). This would rank-order a series of acids or bases with suitable choices for A B. Many such definitions were suggested, but they failed because somewhat different orders were found, depending on the reference reactions chosen. Also, they lacked a theoretical basis linking them to accepted theory. Any numbers obtained were valid only for the chosen reference, and were not transferable. 

We can define alkalinity and acidity in two ways operationally and analytically (or mathematically). Let us first examine the operational definition of alkalinity and then proceed to see how this is related to the mathematical definition when the components of the solution contributing to the alkalinity are only carbonate species and OH". 

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