Factors That Affect Acid Strength

A molecule containing H will act as a proton donor (an acid) only if the H—bond is polarized in this way  

In ionic hydrides, such as NaH, the reverse is true the H atom possesses a n ative charge and behaves as a proton acceptor (a base). Nonpolar H—X bonds, such as the H—C bond in CH4, produce neither acidic nor basic aqueous solutions. 

A third factor that affects the ease with which a hydrogen atom ionizes from HX is the stability of the conjugate base, X. In general, the greater the stability of the conjugate base, the stronger the acid. 

The strength of an acid is often a combination of all three factors. 

A molecule containing H will act as a proton donor (an acid) only if the H—A bond is polarized such that the H atom has a partial positive charge, coo (Section 8.4) Recall that we indicate such polarization in this way  

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Our detailed knowledge of the mechanism of proton transfer from intramolecularly hydrogen-bonded acids and our understanding of the factors that affect the strength of intramolecular hydrogen bonds have now reached a stage when correlations of the proton-transfer behaviour with the nature of the hydrogen bond will soon be possible. 

Understanding the Factors That Affect the Strength of Acids and Bases... 

Structural features are not the only factors that affect acidity or basicity. The same compound can have its acidity or basicity changed when the conditions are changed. The effect of temperature (p. 364) has already been mentioned. More important is the effect of the solvent, which can exert considerable influence on acid and base strengths by differential solvation. If a base is more solvated than its conjugate acid, its stability is increased relative to the conjugate acid. For example,... 

List four factors that affect the strength of an acid. 

EXAMPLE 16-15 Identifying Factors That Affect the Strengths of Acids... 

Oxidation-reduction (redox) reactions, along with hydrolysis and acid-base reactions, account for the vast majority of chemical reactions that occur in aquatic environmental systems. Factors that affect redox kinetics include environmental redox conditions, ionic strength, pH-value, temperature, speciation, and sorption (Tratnyek and Macalady, 2000). Sediment and particulate matter in water bodies may influence greatly the efficacy of abiotic transformations by altering the truly dissolved (i.e., non-sorbed) fraction of the compounds — the only fraction available for reactions (Weber and Wolfe, 1987). Among the possible abiotic transformation pathways, hydrolysis has received the most attention, though only some compound classes are potentially hydrolyzable (e.g., alkyl halides, amides, amines, carbamates, esters, epoxides, and nitriles [Harris, 1990 Peijnenburg, 1991]). Current efforts to incorporate reaction kinetics and pathways for reductive transformations into environmental exposure models are due to the fact that many of them result in reaction products that may be of more concern than the parent compounds (Tratnyek et al., 2003). 

Depending on the relative amylopectimamylose ratio found in the rice, the starch can exhibit a variety of gelatinized textures and strengths, as well as resistance to acid. Overall, there are several basic factors that affect starch performance. These factors, which include rice variety, protein content, method of starch production and modification, are described below. 

Light olefins especially ethylene ( 2 ) and propylene ( 3 ) can be formed from methanol in the MTO process (Chang et al., 1979) using catalyst SAPO-34. Several other catalysts like ZSM-5 (Marchi and Froment, 1991), and Chabazite (Liu et al.. 1984) have been tested. Physical and chemical properties of the catalyst influence its selectivity to hydrocarbons. The physical factors that affect the selectivity of the catalyst are temperature, pressure of the fixed bed reactor, and space velocity of the feed. Other physical characteristics that influence selectivity are crystal size, crystal size distribution, pore size and pore size arrangement. The chemical characteristics that influence the selectivity are acid site density, strength of acid sites, and type of surface acid groups. 

Give two important factors that determine the strength of an acid. How does an increase in each factor affect the acid strength ... 

Example 16-15 illustrates some of the factors affecting acid strength that are discussed in this section. 

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