Weak acid amphiprotic

A similar argument can be used to decide whether an amphiprotic anion such as HC03 or H2PO4- is acidic or basic. In principle, these ions can act as either weak acids or weak bases ... 

If an amphiprotic solvent contains an acid and base that are neither mutually conjugate nor are conjugated with the solvent, a protolytic reaction occurs between these dissolved components. Four possible situations can arise. If both the acid and base are strong, then neutralization occurs between the lyonium ions and the lyate ions. If the acid is weak and the base strong, the acid reacts with the lyate ions produced by the strong base. The opposite case is analogous. A weak acid and a weak base exchange protons ... 

If the dielectric constant of an amphiprotic solvent is small, protolytic reactions are complicated by the formation of ion pairs. Acetic acid is often given as an example (denoted here as AcOH, with a relative dielectric constant of 6.2). In this solvent, a dissolved strong acid, perchloric acid, is completely dissociated but the ions produced partly form ion pairs, so that the concentration of solvated protons AcOH2+ and perchlorate anions is smaller than would correspond to a strong acid (their concentrations correspond to an acid with a pK A of about 4.85). A weak acid in acetic acid medium, for example HC1, is even less dissociated than would correspond to its dissociation constant in the absence of ion-pair formation. The equilibrium... 

Notably, as water has both acid and base properties it is termed amphiprotic and is the most common solvent for acid-base reactions. There are strong acids and weak acids and strong bases and weakbases . The primary feature determining the so-called strength of an acid or base relates to its degree of dissociation in solution, that is, the fraction that produces ions in solution. Importantly, acid or... 

III. Salt of Weak Acid and Weak Base.-Hf both the acid and base from which a given salt is made are weak, the resp( ctive conjugate base and acid will have appreciable strength and consequently will tend to interact with the amphiprotic solvent water. When a salt such as ammonium acetate is dissolved in water, it dissociates almost completely into NH " and Ac" ions, and these acting as acid and base, respectively, take part in the hydrolytic equilibria... 

Amphiprotic substance, when dissolved in a suitable solvent, behaves both as a weak acid and as a weak base. If either its acidic or its basic character predominates sufficiently, titration of the species with a strong base or a strong acid may be feasible. 

The simple amino acids are an important class of amphiprotic compounds that contain both a weak acid and a weak base functional group. When dissolved in water, an amino acid such as glycine undergoes a kind of internal acid/base reaction to produce a zwitterion—a species that bears both a positive and a negative charge. Thus,... 

Define an acid and a base. Distinguish the behavior of strong and weak acids and bases with examples. Define amphiprotic and conjugate acid and base. 

Figure 3.6 depicts the principal primary and secondary equilibria that would be present if oxine is initially dissolved in an appropriate organic solvent that happens to be less dense than water. If this solution is added to an aqueous solution that contains a metal ion such as copper(II) or Cu, two immiscible liquid phases persist. The copper(II) oxinate that initially forms in the aqueous phase, oxine, itself is an amphiprotic weak acid that quickly partitions into the organic phase. Being amphiprotic means that oxine itself can accept a proton from an acid and can also donate one to a base. The degree to which oxine either accepts or donates a proton is governed by the pH of the aqueous solution. The acidic property is the only one considered in the development of the equations considered below. The formation of a Cu oxine chelate can proceed via 1 1 and 1 2 stoichiometry. The fact that it is the 1 2 chelate that is neutral and, therefore, is the dominant form that partitions into the nonpolar solvent is important. All of the competing primary and secondary equilibria can be... 

Oxine, itself being amphiprotic, can exist as either the neutral, weak acid or as a protonated species. A molecular structure for oxine as follows ... 

Amphiprotic solvents consist of liquids, such as water, alcohols and weak organic acids, which are slightly ionised and combine both protogenic and protophilic properties in being able to donate and to accept protons. 

Most protic solvents have both protogenic and protophilic character, i.e. they can split off as well as bind protons. They are called, therefore, amphiprotic. These include water, alcohols, acids (especially carboxylic), ammonia, dimethylsulphoxide and acetonitrile. Solvents that are protogenic and have weak or practically negligible protophilic character include acid solvents, such as sulphuric acid, hydrogen fluoride, hydrogen cyanide, and formic acid. 

Abstract Titration of weak bases in non-aqueous solvents can provide valuable information about these weak bases. Some primary amines 1-aminobutane, 1-aminopropane, 2-aminoheptane, aminocyclohexane, 3-amino-l-phenylbutane were titrated with hydrochloric acid in toluene solvent. All the primary amines gave very well-shaped potentiometric titration curves. The same titrations were done with hydrochloric acid in methanol solvent to show the effect of amphiprotic solvent in the titrations with hydrochloric acid. 

Glacial acetic acid, though like water in being classed as amphiprotic, represents a solvent type distinctly different from water in that it is a much weaker base. This weak basicity makes it a useful solvent for the titration of weakly basic substances. As mentioned in Section 4-3, the autoprotolysis constant has a p T h value of 14.45 for the reaction... 

Neutral solvents The term neutral solvent applies here to solvents not predominately either acidic (protogenic) or basic (protophilic) in character. Some are weakly basic but not appreciably acidic (ethers, dioxane, acetone, acetonitrile, esters), some aprotic (benzene, carbon tetrachloride, 1,2-dichloroethane), and some amphiprotic solvents (ethanol, methanol). Aprotic solvents are used mainly in mixed solvents to alter the solubility characteristics of the reactants. 

Keto-enol tautomerism cannot take place without at least a trace of acid or base, " since the acidic or basic center or both in the tautomeric substance is too weak. In this equilibrium, the heteroatom is the basic site the proton is the acidic site. For tautomerism in general (see p 98), the presence of an acid or a base is not necessary to initiate the isomerization since each tautomeric substance possesses amphiprotic properties. Keto-enol tautomerism is therefore the exception. 

The earliest advantages recognized arose from the use of amphiprotic solvents, those that have both acidic and basic properties. The prototype is water. Significant differences in acid-base properties are seen in the case of either protogenic solvents (more acidic than water), for example acetic acid, or protophilic solvents (more basic than water), for example ethylenediamine. In the protogenic cases it was found that bases too weak to be titrated in water could be successfully titrated with a strong acid dissolved in the same solvent. For example, primary, secondary, and tertiary amines can be titrated in acetic acid with perchloric acid in acetic add as titrant. Medicinal sulfonamides, which have a primary amino group, can be titrated... 

A pH buffer owes its buffering action to the fact that after the addition of hydrogen ions or hydroxyl ions the position of the equilibrium of weakly dissociated electrolytes (acids or bases) is shifted in such a way that the added ions are consumed. This is mainly applicable to aqueous solutions, but the same concept is valid for any amphiprotic solvent. 

Salts Hiat Yield Neutral Solutions 604 Salts Hiat Yield Acidic Solutions 604 Salts Tbat Yield Basic Solutions 604 Salts of Weakly Addic Cations and Weakly Basic Anions 605 Salts of Amphiprotic Anions 605... 

The acidic site and the mechanism of its function were not specified, nor was an example given but it is logical to infer that by the term amphiprotic hydrogen acidic function was meant. If the basic properties of acetonitrile are only slightly stronger than its acidic properties, they must still be deemed very weak. 

---