Weak acids acetic acid

For example, let us contrast the behavior of two weak acids, acetic acid and hydrofluoric acid ... 

We organize this information around the balanced chemical equation, as before. We recognize that as much hydronium ion (a strong acid) as possible will react to produce the weak acid, acetic acid. 

A common weak acid, acetic acid, dissociates according to the following equation ... 

Consider a 0.1 m solution of the weak acid acetic acid = 1-76 X 10 p. a = 4.75). Since the degree of ionization is small, the concentration of undissociated acid may be considered to be approximately the same as the original concentration, i.e. 0.1. The pH can be calculated using the equation... 

Let us consider a weak acid acetic acid (CH3COOH), and its salt, sodium acetate (CHgCOONa). 

Well, in case you hadn t noticed, sodium ions don t seem to do much in chemistry. They are almost always spectator ions, because they don t participate in any of the chemical reactions. Their job is to provide a charge balance to the anions in solution. So, in calculating the pH of sodium acetate, we ignore sodium. The acetate ion, however, is the conjugate base of the weak acid, acetic acid. Therefore, the acetate ion is a base, and we can write this ionization equilibrium equation. 

Hydrogen telluride, generated in situ from aluminum telluride in aqueous tetrahydrofuran containing sulfuric acid, reacted with aliphatic aldehydes to produce dialkyl ditellurium compounds in yields of aproximately 50%. Strong acids are required to obtain acceptable yields of ditellurium compounds. Weak acids (acetic acid, chloroacetic acid) reduce the yields to approximately 10%. In a basic medium (triethylamine), no ditellurium derivative was formed the major product was the alcohol. 

What effect does a ten-fold dilution of a strong acid (hydrochloric acid) have on the pH of the acid What effect does the same dilution of a weak acid (acetic acid) have on its pH Compare the effects for a strong acid and a weak acid. Account for any differences. 

Sodium borohydride reduction of dienamines in the presence of a weak acid (acetic acid or methanol) results in kinetically favoured C-/ protonation followed by rapid hydride addition at C-a17. The method therefore provides a convenient method for converting an a,/ -unsaturated ketone into a y,<5-unsaturated amine as in the synthesis of con-nessine17 (Scheme 11). 

THE PROTOLYSIS OF ACIDS. STRENGTHS OF ACIDS AND BASES It is of interest to examine the processes which take place when an acid is dissolved in a solvent, first of all in water. According to the Br0nsted-Lowry theory this dissolution is accompanied by a protolytic reaction, in which the solvent (water) acts as a base. To elucidate these processes, let us examine what happens if a strong acid (hydrochloric acid) and a weak acid (acetic acid) undergo protolysis. 

The last two reactions are of special interest, since they belong to the category usually known as Misplacement reactions in the first of the two a strong acid, hydrochloric acid, displaces a weak acid, acetic acid, from its salt, while in the second a weak base, e.g., ammonia or an amine, is displaced from its hydrochloride by a strong base. It will be seen later that a much better understanding of these processes can be obtained by treating them as neutralizations, which in fact they are if this term is used in its wider sense. 

The mixture is a buffer solution. It contains nearly equal amounts of the weak acid acetic acid, CH3COOH(o ), and its conjugate base, the acetate ion, CH3COO (a ). It is not necessary that the acid and its conjugate base be present in equal amounts to act as a buffer, but there must be a substantial concentration of each. 

If H+ ions are now added to the buffer solution, they will react with the high concentration of CH3COO present to give undissociated acetic acid. Acetic acid is a weak acid and only dissociates to a small extent, so the pH of the solution does not decrease. In effect, a strong acid such as H+ is mopped up by the buffer to produce a weak acid, acetic acid, which is not sufficiently acidic to lower the pH. 

Figure 18.12 shows chromatograms obtained for the seven mobile phases. Phenols must be separated in weakly acidic (acetic acid) medium, this also having its own effect on selectivity. Hence, the computer calculates slightly different compositions to those described above. The final chromatogram 0 represents the optimum separation obtained out of aU the solvent combinations tested and requires only three components (63% water with 1% acetic acid-34% methanol-3% acetonitrile). 

Look at another system that contains the weak acid acetic acid, HC2H3O2, and the salt sodium acetate, NaC2H302. If a strong base, OH, is added to the buffer system, the weak acid reacts to neutralize the addition. 

For every 250 moieciiles of the weak acid acetic acid, HCiHjOi, added to water, there are about... 

These reactions are very similar, but only the first reaction would be considered an acid-base reaction in the Arrhenius system. In each of the reactions, an H" " is transferred from one reactant to another, but only the first is a reaction between an Arrhenius acid and an Arrhenius base. In the first reaction, an is transferred from the Arrhenius weak acid acetic acid, HC2H302( ), to the Arrhenius weak base ammonia, NH3(<3 ). 

In the second reaction, an H" " is transferred from the Arrhenius weak acid acetic acid,... 

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. 

Buffers, which consist of a weak acid and its conjugate base, cause a solution to resist changes in pH when hydrogen ions or hydroxide ions are added. In Figure 4.7, the pH of a solution of the weak acid acetic acid is graphed as a function of the... 

The anilinium ion is strongly deactivated because of the —I effect of the —NH3+ substituent. Its nitration will yield the meta isomer. The free amine will be strongly activated because of the +M effect of the — NH2 group, and it will yield the para isomer. In the rSatively weak acid, acetic acid, the concentration of the anilinium ion will be much less than in the stronger acids hence no significant amount of the meta isomer is formed. 

In the first one, the termolecular problem (i.e. the fact that in GAC and GBC three molecules have to come together in the transition state) is avoided by making a reaction intramolecular. Normally, ester formation and hydrolysis are specrfic-acid-catalysed only, but here there is catalysis by a weak acid acetic acid. A normal kinetic isotope effect k(HOAc)/k(DOAc) = 2.3 shows that proton transfer occurs in the rate-determining step and there is a large negative AS = -156 J mol" K". This is GAC of nucleophilic attack on a carbonyl group, admittedly in a rather special molecule. 

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