Weak base, acetate

Ethoxide ion, a strong base, removes a proton from acetic acid. The formation of the weak base, acetate ion, in this step drives the equilibrium to the final products, the alcohol and the carboxylate anion. 

A buffer solution consists of 0.5 M acetic acid CH3COOH (Ka value of 1.8 10 M) and 0.5 M sodium acetate CHsCOONa. This solution consists of a weak acid (acetic acid) ad its corresponding weak base (acetate ion). As the amount of the weak acid and weak base are similar (it is sufficient if there just in the same order of magnitude) we have a buffer system. 

Solution We know that the first reaction has to be a radical halogenation because that is the only reaction that an alkane undergoes. Bromination will lead to a greater yield of the desired 2-halo-substituted compound than chlorination will because a bromine radical is more selective than a chlorine radical. To maximize the yield of the desired substitution product over the elimination product, a weak base (acetate ion) is used for the substitution reaction (Section 10.9). The ester is hydrolyzed to an alcohol that forms the target molecule when it is oxidized. 

Aminoazobenzene is a very weak base, and consequently it will not form salts with weak organic acids, such as acetic acid, although it will do so with the strong mineral acids, such as hydrochloric acid. Aminoazobenzene is a yellowish-brown compound, whilst the hydrochloride is steel blue. The colour of the latter is presumably due to the addition of the proton to the phenyl-N-atom, the cation thus having benzenoid and quinonoid forms ... 

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... 

Weak bases only partially accept protons from the solvent and are characterized by a base dissociation constant, kj,. For example, the base dissociation reaction and base dissociation constant for the acetate ion are... 

At the equivalence point, the moles of acetic acid initially present and the moles of NaOH added are identical. Since their reaction effectively proceeds to completion, the predominate ion in solution is CH3COO-, which is a weak base. To calculate the pH we first determine the concentration of CH3COO-. 

All other things being equal, the strength of a weak acid increases if it is placed in a solvent that is more basic than water, whereas the strength of a weak base increases if it is placed in a solvent that is more acidic than water. In some cases, however, the opposite effect is observed. For example, the pKb for ammonia is 4.76 in water and 6.40 in the more acidic glacial acetic acid. In contradiction to our expectations, ammonia is a weaker base in the more acidic solvent. A full description of the solvent s effect on a weak acid s piQ or on the pKb of a weak base is beyond the scope of this text. You should be aware, however, that titrations that are not feasible in water may be feasible in a different solvent. 

The NH3 is removed by distillation and titrated with HCl. Alternatively, N03 can be titrated as a weak base in an acidic nonaqueous solvent such as anhydrous acetic acid, using HCIO4 as a titrant. 

Trifluoromethylpyridine can be prepared ia 54% yield from picolinic acid and sulfur tetrafluoride—hydrogen fluoride (434). 2-Trifluoromethylpyridine is a weak base no hydrochloride salt is formed. However, 2-trifluoromethylpyridine 1-oxide [22253-71-0] (bp 132—133°C/2.7 kPa (20 mm Hg)) is prepared ia 81% yield usiag 30% hydrogen peroxide—acetic acid (438). 

Chemical Properties. Trimethylpentanediol, with a primary and a secondary hydroxyl group, enters into reactions characteristic of other glycols. It reacts readily with various carboxyUc acids and diacids to form esters, diesters, and polyesters (40). Some organometaUic catalysts have proven satisfactory for these reactions, the most versatile being dibutyltin oxide. Several weak bases such as triethanolamine, potassium acetate, lithium acetate, and borax are effective as stabilizers for the glycol during synthesis (41). 

Most weak base anion exchangers adsorbweak organic acids such as formic acid [64-18-6] and acetic acid [64-19-7] but do not remove weak organic acids such as carbonic acid [463-79-6] or siHcic acid [7669-41 ]. 

It is for this reason that the action of acetic anhydride is utilised, whic h only unites with tlie jirimary and secondary base. Diwiethylaniline is a weak base, which, like aniline, is neutral... 

Quinoxalin-2-one is a very weak base (pK — 1.37) and so the different orientation of substitution in acetic and sulfuric acids may mean that in acetic acid the principal species undergoing nitration is the neutral molecule, and in sulfuric acid, the mono-cation. Treatment of quinoxaline-2,3-dione, or its iViV -dimethyl derivative in sulfuric acid, with 1 equivalent of potassium nitrate, results in nitration at position 6 with 2 equivalents of potassium nitrate, 6,7-dinitro compounds are formed. When quinoxaline is boiled with aqueous nitric acid, 6-... 

Notice that this reaction is the reverse of the reaction of the weak base QH - (the acetate ion) with water (Chapter 13). It follows from the reciprocal rule that for this reaction,... 

The CH3COOH2 ion so formed can very readily give up its proton to react with a base. A weak base will, therefore, have its basic properties enhanced, and as a consequence titrations between weak bases and perchloric acid can frequently be readily carried out using acetic acid as solvent. 

It may be noted that very weak acids, such as boric acid and phenol, which cannot be titrated potentiometrically in aqueous solution, can be titrated conductimetrically with relative ease. Mixtures of certain acids can be titrated more accurately by conductimetric than by potentiometric (pH) methods. Thus mixtures of hydrochloric acid (or any other strong acid) and acetic (ethanoic) acid (or any other weak acid of comparable strength) can be titrated with a weak base (e.g. aqueous ammonia) or with a strong base (e.g. sodium hydroxide) reasonably satisfactory end points are obtained. 

Weak acids with weak bases. The titration of a weak acid and a weak base can be readily carried out, and frequently it is preferable to employ this procedure rather than use a strong base. Curve (c) in Fig. 13.2 is the titration curve of 0.003 M acetic acid with 0.0973 M aqueous ammonia solution. The neutralisation curve up to the equivalence point is similar to that obtained with sodium hydroxide solution, since both sodium and ammonium acetates are strong electrolytes after the equivalence point an excess of aqueous ammonia solution has little effect upon the conductance, as its dissociation is depressed by the ammonium salt present in the solution. The advantages over the use of strong alkali are that the end point is easier to detect, and in dilute solution the influence of carbon dioxide may be neglected. 

Tetrakis(tripheiiylphosphine)palladium(0) is often used for this reaction. However, Pd(II) complexes such as bis(triphenylphosphine)palladium dichloride or palladium acetate are also commonly employed for convenience, as they are stable in ah. The base is typically a secondary or tertiary amine such as triethy-lamine. Weak bases such as sodium (potassium) acetate, bicarbonate, or carbonate are also used. 

Solutions of different acids having the same concentration might not have the same pH. For instance, the pH of 0.10 M CH3COOH(aq) is close to 3 but that of 0.10 M HCl(aq) is close to 1. We have to conclude that the concentration of H,() ions in 0.10 M CH3COOH(aq) is lower than that in 0.10 M HCl(aq). Similarly, we find that the concentration of OH ions is lower in 0.10 M NH,(aq) than it is in 0.10 M NaOH(aq). The explanation must be that in water CH.COOH is not fully deprotonated and NH3 is not fully protonated. That is, acetic acid and ammonia are, respectively, a weak acid and a weak base. The incomplete deprotonation of CH3COOH explains why solutions of HC1 and CH3COOH with the same molarity react with a metal at different rates (Fig. 10.14). 

Acetic acid is used as a solvent for some reactions between acids and bases, (a) Nitrous acid and carbonic acids are both weak acids in water. Will either of them act as a strong acid in acetic acid Explain your answer, (b) Will ammonia act as a strong or weak base in acetic acid Explain your answer. 

The most important type of mixed solution is a buffer, a solution in which the pH resists change when small amounts of strong acids or bases are added. Buffers are used to calibrate pH meters, to culture bacteria, and to control the pH of solutions in which chemical reactions are taking place. They are also administered intravenously to hospital patients. Human blood plasma is buffered to pH = 7.4 the ocean is buffered to about pH = 8.4 by a complex buffering process that depends on the presence of hydrogen carbonates and silicates. A buffer consists of an aqueous solution of a weak acid and its conjugate base supplied as a salt, or a weak base and its conjugate acid supplied as a salt. Examples are a solution of acetic acid and sodium acetate and a solution of ammonia and ammonium chloride. 

The azide ion is a weak base and accepts a proton to form its conjugate acid, hydrazoic acid, HN3. Hydrazoic acid is a weak acid similar in strength to acetic acid. 

Acetic acid is a weak acid, acetate anion is a weak base, water can act as an acid or a base, and Na+ is a spectator ion. These species are reactants in three acid-base equilibria ... 

A third approach to buffer solutions is to add strong acid to a solution of a weak base. This produces a buffer solution if the amount of strong acid is about half the amount of weak base. Continuing with our examples of acetic acid-acetate buffers, if a solution of hydrochloric acid is added to a solution of sodium acetate, then hydronium ions react quantitatively with acetate anions ... 

HCl H3 O " and Cl Sodium acetate CH3 CO2 andNa Because the hydronium ion is a strong acid and the acetate anion is a weak base, mixing the solutions results in near-quantitative reaction between these two ions ... 

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