Acidity exponent

Substance Tempera- ture Constant Acid Exponent pK... 

Because the concentration of ions in solution generally is quite small one has for the sake of convenience chose to express a solutions acidness based on the decimal logarithm to the concentration of BT ions completely analogous to the principles that the acid constant Ka was expressed as an acid exponent pKa. this is known as the pH scale and the pH values are defined as ... 

The buffer equation is also known as the Henderson-Hasselbalch equation. This equation is in principle just another version of the expression for Ka but it may nevertheless other be easier to apply. Using the buffer equation one must remember that HA and A denotes the corresponding acid-base pair and that pKa is the acid exponent of the acid (HA). In the following example the buffer effect is illustrated in a buffer system consisting of equal amounts of acetic acid and acetate into which strong base is added. 

Such a ratio has been called an acidity exponent, a. Values for a number of aromatic substrates, together with the corresponding Bronsted exponents, are listed in Table 2. The Bronsted exponents... 

A persistent idea is that there is a very small number of flavor quaUties or characteristics, called primaries, each detected by a different kind of receptor site in the sensory organ. It is thought that each of these primary sites can be excited independently but that some chemicals can react with more than one site producing the perception of several flavor quaUties simultaneously (12). Sweet, sour, salty, bitter, and umami quaUties are generally accepted as five of the primaries for taste sucrose, hydrochloric acid, sodium chloride, quinine, and glutamate, respectively, are compounds that have these primary tastes. Sucrose is only sweet, quinine is only bitter, etc saccharin, however, is slightly bitter as well as sweet and its Stevens law exponent is 0.8, between that for purely sweet (1.5) and purely bitter (0.6) compounds (34). There is evidence that all compounds with the same primary taste characteristic have the same psychophysical exponent even though they may have different threshold values (24). The flavor of a complex food can be described as a combination of a smaller number of flavor primaries, each with an associated intensity. A flavor may be described as a vector in which the primaries make up the coordinates of the flavor space. 

In some cases, the exponent is unity. In other cases, the simple power law is only an approximation for an actual sequence of reactions. For instance, the chlorination of toluene catalyzed by acids was found to have CL = 1.15 at 6°C (43°F) and 1.57 at 32°C (90°F), indicating some complex mechanism sensitive to temperature. A particular reaction may proceed in the absence of catalyst out at a reduced rate. Then the rate equation may be... 

There are many reactions in which the products formed often act as catalysts for the reaction. The reaction rate accelerates as the reaction continues, and this process is referred to as autocatalysis. The reaction rate is proportional to a product concentration raised to a positive exponent for an autocatalytic reaction. Examples of this type of reaction are the hydrolysis of several esters. This is because the acids formed by the reaction give rise to hydrogen ions that act as catalysts for subsequent reactions. The fermentation reaction that involves the action of a micro-organism on an organic feedstock is a significant autocatalytic reaction. 

The values of Ka and Kb for different acids and bases vary through many powers of ten. It is often convenient to use the dissociation constant exponent pK defined by... 

The fact that the experimentally determined exponent of h0 in Scheme 3-25 is not an integer ( — 2), as expected for the mechanism discussed here, is due to the complexity of concentrations and activities in highly acidic solutions. In 66-74% H2S04 the rate is propotional to ho2A. Concerning the subscript 6, see the footnote explaining this point for Schemes 3-12 to 3-14. 

Equation (1.20) is frequently used to correlate data from complex reactions. Complex reactions can give rise to rate expressions that have the form of Equation (1.20), but with fractional or even negative exponents. Complex reactions with observed orders of 1/2 or 3/2 can be explained theoretically based on mechanisms discussed in Chapter 2. Negative orders arise when a compound retards a reaction—say, by competing for active sites in a heterogeneously catalyzed reaction—or when the reaction is reversible. Observed reaction orders above 3 are occasionally reported. An example is the reaction of styrene with nitric acid, where an overall order of 4 has been observed. The likely explanation is that the acid serves both as a catalyst and as a reactant. The reaction is far from elementary. 

Lux (1939) introduced the symbol pO (note it is not an exponent like pH) to quantify the acid-base balance in a glass, and various attempts have been made to obtain values for this parameter. All are based on the electronegativity of the cation or a related characteristic, such as electrostatic field strength (Volf, 1984). 

An autocatalytic reaction is one in which the reaction rate is proportional to a product concentration raised to a positive exponent. Some of the first articles in the literature of chemical kinetics deal with reactions of this type. For example, in 1857, Baeyer (12) reported that the reaction of bromine with lactose was autocatalytic. The hydrolyses of several esters also fit into the autocatalytic category, since the acids formed by reaction give rise to hydrogen ions that serve as catalysts for subsequent reaction. Among the most significant autocatalytic reactions are the fermentation reactions that involve the action of a microorganism on an organic feedstock. 

Since it is experimentally observed that carboxylic acids are required to promote glycol production by this system and since acid concentration appears in the empirical rate equation for glycol production with a substantial exponent (ca. 1.8) the formation of a metal-carbon bonded intermediate (step 6) may... 

NOTE. The coefficient and exponent of the rate equation are strong functions of the sulfuric acid concentration. 

Linderic acid, physical properties, 5 31t Linde sieve tray, 23 338 Lind, James, 25 746-747 Linear geometry, for metal coordination numbers, 7 574, 575t Linear 1-olefins, properties of, 17 711t Linear acceleration, exponents of... 

Permanganate production, 9 635-636 Permanganate salts, 15 609 Permanganic acid, 15 596 Permanganyl fluoride, 15 597 Permanox, 15 587—588 Permeabihty, 3 375—380 colloids, 7 276-277 of common materials, 11 332t dimensions of, 3 378-380 Ergun equation for, 11 332-333 exponents of dimensions, 8 585t of filled polymers, 11 303, 310-311 moisture, 10 2... 

Figures 1 and 2 show the corresponding conversTon curves in toluene and in methanol solutions respectively. In the latter case log-log coordinates are used to represent the data. The conversion curves are then linear and their slope B, which is the exponent of time in the relation per cent conversion = Kt, measures the extent of auto-acceleration. B is referred to as the "auto-accele-ration index". For pure acrylic acid B = 1.8 - 2.0 in non polar solvents 3 tends towards unity.

The rate-enhancing effect of cationic detergents was analyzed by using Hill s equation. The observed exponent (n = 3 — 4) suggests that polymer-bound detergents facilitate the subsequent binding acceleratively hence the sigmoidshaped dissociation behavior of hydroxamic acid. 

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