Acetic acid conjugate base

Buffer solutions have two important characteristics. One of these characteristics is the pH of the solution. The other is its buffer capacity the amount of acid or base that can be added before considerable change occurs to the pH. The buffer capacity depends on the concentration of the acid/conjugate base (or the base/conjugate acid) in the buffer solution. When the ratio of the concentration of the buffer components is close to 1, the buffer capacity has reached its maximum. As well, a buffer that is more concentrated resists changes to pH more than than a buffer that is more dilute. This idea is illustrated in Figure 8.10, with buffer solutions of acetic acid and acetate of different concentrations. 

Recall, from Chapter 8, that a buffer consists of a weak acid/conjugate base mixture or a weak base/conjugate acid mixture. One buffer that you examined previously contains acetic acid and sodium acetate. The common-ion effect applies to this buffer. The equilibrium of the acetic acid is affected by the common acetate ion from sodium acetate. 

Conjugate base of acetic acid) Weak base... 

Thus, the H30+ concentration in a buffer solution has a value close to the value of Ka for the weak acid but differs by a factor equal to the concentration ratio [weak acid]/[conjugate base]. In the 0.10 M acetic acid-0.10 M sodium acetate solution, where the concentration ratio is unity, [H30 + ] equals Ka ... 

The tetrazole synthesis was done with azide and acetic acid and base-catalysed conjugate addition followed by treatment with SOCl2, to make the acid chloride, and piperidine completed the synthesis.13... 

Consider the buffer solution prepared by mixing together acetic acid—HC2H3O2—and sodium acetate—C2H3O2- containing Na+ as a spectator ion (See Skill 2.1b). The equilibrium reaction for this acid/conjugate base pair is ... 

The addition of the strong acid induces the protonation of the conjugate base of the weak acid. The weak acid is less ionized when the strong acid is present than when it is alone at the same concentration. This phenomenon is called ionization repression (of the weak acid). The weak acid dissociation is repressed. For example, in a solution of 10 " mol/L of hydrochloric acid and 10 mol/L of acetic acid, calculations based on the principles recalled above give the result [H3O+] = 4.71 X 10 " mol/L. In a solution of acetic acid alone at the same analytical concentration, C = 1.0 x 10 mol/L, calculations give 4.18 x 10 " mol/L. In the mixture of both acids, the acidity due to acetic acid can be calculated by taking away the hydrochloric acid s acidity from the total acidity ... 

You are asked to make a buffer with a pH value close to 4 that would best resist an increase in pH. You can select one of the following acid-conjugate base pairs acetic acid-acetate. Kg = 1.8 x 10 ammonium ion-ammonia. Kg = 5.6 X 10 ° or benzoic acid-benzoate, Kg = 6.3 x 10 and you can mix them in the following acid-conjugate base ratios 1 1, 2 1, or 1 2. What combination would make the best buffer ... 

Example A common misconception is that the conjugate base of a weak acid is strong This is sometimes but not always true It is true for example for ammo nia which is a very weak acid (pK 36) Its conjugate base amide ion (H2N ) is a much stronger base than HO It is not true however for acetic acid both acetic acid and its conjugate base acetate ion are weak The conjugate base of a weak acid will be strong only when the acid is a weaker acid than water... 

Citing amine basicity according to the of the conjugate acid permits acid-base reac tions involving amines to be analyzed according to the usual Brpnsted relationships For example we see that amines are converted to ammonium ions by acids even as weak as acetic acid... 

The most common charge types for the acid HB and its conjugate base B are CH3COOH = H+ -f CH3C00 (acetic acid, acetate ion)... 

When an acid and a base react, the products are a new acid and base. For example, the acetate ion, C1T3COO-, in reaction 6.7 is a base that reacts with the acidic ammonium ion, N1T45", to produce acetic acid and ammonia. We call the acetate ion the conjugate base of acetic acid, and the ammonium ion is the conjugate acid of ammonia. 

Weak acids, of which aqueous acetic acid is one example, cannot completely donate their acidic protons to the solvent. Instead, most of the acid remains undissociated, with only a small fraction present as the conjugate base. 

Tabulating Values for K and Kb A useful observation about acids and bases is that the strength of a base is inversely proportional to the strength of its conjugate acid. Consider, for example, the dissociation reactions of acetic acid and acetate. 

Adding NaOH converts a portion of the acetic acid to its conjugate base. 

A wide variety of /3-lactams are available by these routes because of the range of substituents possible in either the ketene or its equivalent substituted acetic acid derivative. Considerable diversity in imine structure is also possible. In addition to simple Schiff bases, imino esters and thioethers, amidines, cyclic imines and conjugated imines such as cinnamy-lidineaniline have found wide application in the synthesis of functionalized /3-lactams. A-Acylhydrazones can be used, but phenylhydrazones and O-alkyloximes do not give /3-lactams. These /3-lactam forming reactions give both cis and /raMS-azetidin-2-ones some control over stereochemistry can, however, be exercised by choice of reactants and conditions. 

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. 

This relationship is known as the Henderson-Hasselbalch equation. Thus, the pH of a solution can be calculated, provided and the concentrations of the weak acid HA and its conjugate base A are known. Note particularly that when [HA] = [A ], pH = pAl,. For example, if equal volumes of 0.1 MHAc and 0.1 M sodium acetate are mixed, then... 

The shapes of the titration curves of weak electrolytes are identical, as Figure 2.13 reveals. Note, however, that the midpoints of the different curves vary in a way that characterizes the particular electrolytes. The pV, for acetic acid is 4.76, the pV, for imidazole is 6.99, and that for ammonium is 9.25. These pV, values are directly related to the dissociation constants of these substances, or, viewed the other way, to the relative affinities of the conjugate bases for protons. NH3 has a high affinity for protons compared to Ac NH4 is a poor acid compared to HAc. 

Hydronium ion, the product that results when the base H20 gains a proton, is called the conjugate acid of the base, and chloride ion, the product that results when the acid HCI loses a proton, is called the conjugate base of the acid. Other common mineral acids such as H2S04 and HNOj behave similarly, as do organic acids such as acetic acid, CH2C02H. 

Electrostatic potential maps of the conjugate bases from methanol, acetic acid, and acetone are shown in Figure 2.4. As you might expect, all three show a substantial amount of negative charge (red) on oxygen. 

To set the stage for the crucial carbene insertion reaction, the acetic acid side chain in 32 must be homologated. To this end, treatment of 32 with 1,l -carbonyldiimidazole furnishes imidazo-lide 33, a competent acylating agent, which subsequently reacts with the conjugate base of Meldrum s acid (34) to give 35. Solvolysis of this substance with para-nitrobenzyl alcohol in acetonitrile at reflux provides /Mceto ester 36 after loss of one molecule of ace-... 

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,... 

Our first task is to calculate the pH of a solution of a weak acid, such as acetic acid in water The initial concentration of the acid is its concentration as prepared, as if no acid molecules had donated any protons. For a strong acid HA, the H30+ concentration in solution is the same as the initial concentration of the strong acid, because all the HA molecules are deprotonated. However to find the H30 concentration in a solution of a weak acid HA, we have to take into account the equilibrium between the acid HA, its conjugate base A-, and water (Eq. 8). We can expect the pH to lie somewhere between 7, a value indicating no deprotonation, and the value that we would calculate for a strong acid, which undergoes complete deprotonation. The Technique, which is based on the use of an equilibrium table like those introduced in Chapter 9, is set out in Toolbox 10.1. 

We have seen how to estimate the pH of a solution of a weak acid or base (Chapter 10), but suppose that a salt of the acid or base is also present. How does that salt affect the pH of the solution Suppose we have a dilute hydrochloric acid solution and add to it appreciable concentrations of the conjugate base, the Cl- ion, as sodium chloride. Because the acid is strong, its conjugate base is extremely weak and so has no measurable effect on pH. The pH of 0.10 M HCl(aq) is about 1.0, even after 0.10 mol NaCl has been added to a liter of the solution. Now suppose instead that the solution contains acetic acid to which sodium acetate has been added (the acetate ion, CH jC()2, is the conjugate base of CH COOH). Because the conjugate base of a weak acid is a base, we can predict that adding acetate ions (as sodium acetate) to a solution of acetic acid will increase the pH of the solution. Similarly, suppose we have a solution of ammonia and add ammonium chloride to it. The... 

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