Relative Acid Strength

Note that the concentration of H2O is omitted from the expression because its value is so large that it is unaffected by the dissociation reaction.The magnitude of provides information about the relative strength of a weak acid, with a smaller corresponding to a weaker acid. The ammonium ion, for example, with a Ka of 5.70 X 10 °, is a weaker acid than acetic acid. 

Procedures to compute acidities are essentially similar to those for the basicities discussed in the previous section. The acidities in the gas phase and in solution can be calculated as the free energy changes AG and AG" upon proton release of the isolated and solvated molecules, respectively. To discuss the relative strengths of acidity in the gas and aqueous solution phases, we only need the magnitude of —AG and — AG" for haloacetic acids relative to those for acetic acids. Thus the free energy calculations for acetic acid, haloacetic acids, and each conjugate base are carried out in the gas phase and in aqueous solution. 

Fiber Relative strength Specific gravity Normal moisture content (%) Maximum usable temperature ( F) Acid Base Organic solvent Other attribute... 

Table 2.3 Relative Strengths of Some Common Acids and Their Conjugate Bases...

I Table 13.4 Relative Strengths of Brensted-Lowry Acids and Bases ... 

Table 11-1V. relative strengths of acids in aqueous solution... 

Brdnsted-Lowry theory, 194 contrast definitions, 194 indicators, 190 reactions, 188 titrations, 188 Acids, 183 aqueous, 179 carboxylic, 334 derivatives of organic, 337 equilibrium calculations, 192 experimental introduction, 183 names of common, 183 naming of organic, 339 properties of, 183 relative strengths, 192, 451 strength of, 190 summary, 185 weak, 190, 193 Actinides, 414 Actinium... 

To express the relative strengths of an acid and its conjugate base (a conjugate acid-base pair ), we consider the special case of the ammonia proton transfer equilibrium, reaction C, for which the basicity constant was given earlier (Kb = [NH4+l[OH ]/ NH3]). Now let s consider the proton transfer equilibrium of ammonia s conjugate acid, NH4+, in water ... 

Because all the hydrohalic acids except HF are strong acids, they arc leveled in water. Therefore, to determine their relative strengths, they must be studied in a solvent that is a poorer proton acceptor than water (such as pure acetic acid). 

Use K, values to predict the relative strengths of two acids or two bases (Example 10.5). 

Predict the relative strengths of acids from molecular structures (Example 10.6). 

Sections 10.9 and 10.10 discuss the relationship between molecular structure and the strengths of acids. The same ideas can be applied to bases, (a) Explain the relative strengths of the bases OH, NH,, and CH. (see Table 10.3). 

This is always the case for any two acids, and by measuring the positions of the equilibrium the relative strengths of acids and bases can be determined. Of course, if the two acids involved are close to each other in strength, a measurable reaction will occur from both sides, though the position of equilibrium will still be over to the... 

We express the relative strengths of weak acids and bases in terms of their dissociation constants. Shown... 

Apart from the hardness and softness, two reactivity-related features need to be pointed out. First, iron salts (like most transition metal salts) can operate as bifunctional Lewis acids activating either (or both) carbon-carbon multiple bonds via 71-binding or (and) heteroatoms via a-complexes. However, a lower oxidation state of the catalyst increases the relative strength of coordination to the carbon-carbon multiple bonds (Scheme 1). 

Solvent effects on the magnitude of spin-spin coupling constants in phosphoryl compounds have been reported, as have the solvent effects on the relative strengths of phosphoric acid and some of its partially esterified derivatives.The variation of i.r. frequencies of (122) and (123)... 

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. 

Monofunctional and Polyfunctional Electrodes At monofunctional electrodes, one sole electrode reaction occurs under the conditions specified when current flows. At polyfunctional electrodes, two or more reactions occur simultaneously an example is the zinc electrode in acidic zinc sulfate solution. When the current is cathodic, metallic zinc is deposited at the electrode [reaction (1.21)] and at the same time, hydrogen is evolved [reaction (1.27)]. The relative strengths of the partial currents corresponding to these two reactions depend on the conditions (e.g., the temperature, pH, solution purity). Conditions may change so that a monofunctional electrode becomes polyfunctional, and vice versa. In the case of polyfunctional electrodes secondary (or side) reactions are distinguished from the principal (for the given purpose) reaction (e.g., zinc deposition). In the electrolytic production of substances and in other practical applications, one usually tries to suppress all side reactions so that the principal (desired) reaction will occur with the highest possible efficiency. 

While the pH scale has made it convenient to describe the order of hydrogen ion concentrations and to give a measure of the acid strength or alkalinity of a solution, it suffers from a defect which is less obvious. A 4 10-5 N HC1 solution is clearly twice as acidic as a 2 10-5 N solution, but the pH values of these solutions, 4.40 and 4.70, provide no idea of the relative strengths of these solutions. 

Thus, the relative strengths of the acid (small pX (HA)) and of the base (large p/Ca(BH+)) decide whether the solution becomes acidic or alkaline. 

Elanany, M., Koyama, M., Kubo, M. el al. (2005) Periodic density functional investigation of Lewis acid sites in zeolites Relative strength order as revealed from NH3 adsorption, Appl. Surf. Sci., 246, 96. 

Part LIII. The Relative Strengths of Some Unsaturated Carboxylic Acids. J. Chem. Soc. [London] 1956, 4761. 

Table 3.1 Relative Strength of Selected Acids and their Conjugate Bases... 

The hard-soft acid-base principle is not restricted to the usual types of acid-base reactions. It is a guiding principle that for all types of interactions species of similar electronic character interact best. We have already seen some applications (such as the relative strength of HF and HI) of this principle, which we will continue to call HSAB, but we now consider a number of other types of applications. 

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