Conjugate acid and

Product acids and bases such as those formed in this process are termed conjugate acids and conjugate bases. Thus, all acid-base reactions can be written as... 

If the observed second-order rate constant is greater than calc., reaction via the free base is precluded. If /taobs. is less than k czlc., reaction via the conjugate acid or the free base is possible. The first compound reported to be nitrated via its conjugate acid, and yet to have 2 calc. > obs. at the acidities concerned, was pyrazoleother examples are mentioned later ( 9.3 10.4.2). 

Comparison of the behaviour of cinnoline 2-oxide (vi, i = O) with that of 2-methoxycinnolinium (vi, R = OMe) suggests that at high acidities the former is nitrated as its conjugate acid (vi, R = OH), but that as the acidity is lowered the free base becomes active. At high acidities 5- and 8-nitration are dominant, but as the acidity is lowered 6-nitration becomes increasingly important. The 5- and 8-nitro compounds are probably formed mainly or wholly by nitration of the conjugate acid, and the 6-nitro compound wholly or mainly from the free base. ... 

In the equation shown the base uses an unshared pair of electrons to remove a proton from an acid The base is converted to its conjugate acid, and the acid is converted to... 

Figure 1 The tt-electron densities in imidazole, its conjugate acid and base, and pyrazole...

The NMR spectra of pyrazolium and indazolium ions have been widely studied (Table 10), including both the conjugate acids and the quaternary salts. The spectra obtained in sulfuric acid prove unquestionably that the protonation of these species takes place at position 2 (Section 4.04.2.1.3(iv)). 

Use curved arrows to track electron movement and identify the acid, base, conjugate acid, and conjugate base. 

Explain why, in the study of an acid-base equilibrium, we observe absorption peaks of both species (conjugate acid and base) when using electronic absorption spectroscopy, but only a single peak by NMR. 

An inflection point in a pH-rate profile suggests a change in the nature of the reaction caused by a change in the pH of the medium. The usual reason for this behavior is an acid-base equilibrium of a reactant. Here we consider the simplest such system, in which the substrate is a monobasic acid (or monoacidic base). It is pertinent to consider the mathematical nature of the acid-base equilibrium. Let HS represent a weak acid. (The charge type is irrelevant.) The acid dissociation constant, = [H ][S ]/[HS], is taken to be appropriate to the conditions (temperature, ionic strength, solvent) of the kinetic experiments. The fractions of solute in the conjugate acid and base forms are given by... 

Figure 6-9. Variation with pH of the fractions Fhs (conjugate acid) and Fs (conjugate base) for an acid with pK = 4.0.

Pulse radiolysis. Consider the reaction shown in Eq. (11-58). Show that H and e q are related as conjugate acid and base. Calculate the pKa of H. ... 

EXAMPLE 10.1 Sample exercise Writing the formulas of conjugate acids and bases... 

Because conjugate acids and bases are in equilibrium in solution, we use the equilibrium constant for proton transfer between the solute and the solvent as an indicator of the strength of an acid or a base. For example, for acetic acid in water,... 

Write the formulas for conjugate acids and bases (Example 10.1). 

Buffers are often prepared with equal molar concentrations of the conjugate acid and base. In these equimolar solutions,... 

This very simple result makes it easy to make an initial choice of a buffer we just select an acid that has a pfC, close to the pH that we require and prepare an equimolar solution with its conjugate base. When we prepare a buffer for pH > 7 we have to remember that the acid is supplied by the salt, that the conjugate base is the base itself, and that the pKa is that of the conjugate acid of the base (and hence related to the pKh of the base by pR l + pKh = p/conjugate acid and base have unequal concentrations—such as those considered in Examples 11.1 and 11.2—are buffers, but they may be less effective than those in which the concentrations are nearly equal (see Section 11.3). Table 11.1 lists some typical buffer systems. 

Step 4 Find the molarities of the conjugate acid and base in solution. Use J1 = /V, where V is the total volume of the solution, V = Vanalvtc + Vtltrjllt. 

Step 5 Use an equilibrium table to find the H.O concentration in a weak acid or the OH concentration in a weak base. Alternatively, if the concentrations of conjugate acid and base calculated in step 4 are both large relative to the concentration of hydronium ions, use them in the expression for /<, or the Henderson—Hasselbalch equation to determine the pH. In each case, if the pH is less than 6 or greater than 8, assume that the autoprotolysis of water does not significantly affect the pH. If necessary, convert between Ka and Kh by using Kw = KA X Kb. 

FIGURE 11.10 The stoichiometric point of an acid base titration may be detected by the color change of an indicator. Here we see the colors of solutions containing a few drops of phenolphthalein at (from left to right) pH of 7.0, 8.5, 9.4 (its end point), 9.8, and 12.0. At the end point, the concentrations of the conjugate acid and base forms of the indicator are equal... 

Aufbau principle See building-up principle. autoionization See autoprotolysis. autoprotolysis A reaction in which a proton is transferred between two molecules of the same substance. The products are the conjugate acid and conjugate base of the substance. Example ... 

Heisenberg uncertainty principle If the location of a particle is known to within an uncertainty Ax, then the linear momentum parallel to the x-axis can he known only to within an uncertainty Ap, where ApAx > till. Henderson-Hasselbalch equation An approximate equation for estimating the pH of a solution containing a conjugate acid and base. See also Section 11.2. Henry s constant The constant kH that appears in Henry s law. 

C17-0018. Identify the conjugate acid and the conjugate base of the dihydrogen phosphate anion, H2 PO4, and the hydrogen phosphate anion, HP04. ... 

C17-0076. Write aii the conjugate acid-base equiiibrium expressions that appiy to an aqueous soiution of each of the substances in Probiem, and identify each conjugate acid and base. 

C17-0119. Aqueous solutions of Na2 SO3 and CH3 CO2 H are mixed, (a) List the major species in each solution, (b) Write the net ionic reaction that occurs on mixing, (c) Identify the acid, base, conjugate acid, and conjugate base. 

Ephedrine is a weak base, so = 9.1 X 10 is a reasonable value. At the stoichiometric point, the only major species present are the conjugate acid and water, so the acidic pH of 5.63 is also reasonable. 

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