Conjugate base, definition

Buffers are solutions that tend to resist changes in their pH as acid or base is added. Typically, a buffer system is composed of a weak acid and its conjugate base. A solution of a weak acid that has a pH nearly equal to its by definition contains an amount of the conjugate base nearly equivalent to the weak acid. Note that in this region, the titration curve is relatively flat (Figure 2.15). Addition of H then has little effect because it is absorbed by the following reaction ... 

The products of proton transfer in aqueous solution may also react with water. For example, the CIST ion produced when HCN loses a proton to water can accept a proton from a water molecule and form HCN again. Therefore, according to the Bronsted definition, CN is a base it is called the conjugate base of the acid HCN. In general, a conjugate base of an acid is the species left when the acid donates a proton ... 

The chlorine ion can now accept a proton (and become hydrochloric acid again). If the chlorine can accept a proton, according to the Bronsted-Lowry definition, it is a base. Chemists actually call this chlorine ion the conjugate base of hydrochloric acid. Any time an acid gives up its proton, the substance that is left over can act as a base. So every acid has a conjugate base. 

By definition, an acid will donate a proton to a base, and it is converted into its conjugate base. Conversely, a base will accept a proton from a... 

Drugs cross biological membranes most readily in the unionised state. The unionised drug is 1000-10000 times more lipid-soluble than the ionised form and thus is able to penetrate the cell membrane more easily. Chemical compounds in solution are acids, bases or neutral. The Bronsted-Lowry definition of an acid is a species that donates protons (H+ ions) while bases are proton acceptors. Strong acids and bases in solution dissociate almost completely into their conjugate base and H+. Weak acids and weak bases do not completely dissociate in solution, and exist in both ionised and unionised states. Most drugs are either weak acids or weak bases. For an acid, dissociation in solution is represented by ... 

The "salt" or conjugate base, A, is the ionized form of a weak acid. By definition, the dissociation constant of the acid, Ka, is... 

Note that this definition is different in at least two major respects from the conventional definition of an arid as a substance dissociating to give H+ in water. The Lowry-Brnsted definition states that for every acid there be a conjugate base, and vice versa. Thus, in the examples cited above. Cl-. OH-, and NH--are the conjugate bases of HCl, H20. and NH3. 

According to this definition, C032- is the conjugate base of HC03 and O2 is the conjugate base of OH. ... 

A weak acid is one that is only partially dissociated in water. Only a small fraction of the weak acid molecules transfer a proton to water, and the solution therefore contains mainly undissociated HA molecules along with small amounts of H30+ and the conjugate base A-. Typical weak acids are nitrous acid (HNO2), hydrofluoric acid (HF), and acetic acid (CH3C02H). In the case of very weak acids such as NH3, OH-, and H2, the acid has practically no tendency to transfer a proton to water, and the acid-dissociation equilibrium lies essentially 100% to the left. It follows from this definition that very weak acids have strong conjugate... 

For most aqueous acid-base chemistry, the Lewis definitions are too general and lack the symmetry of the acid-conjugate base relationship. We will mostly use the Bronsted-Lowry definitions. 

This is an amphoteric compound because it behaves as both an acid and a base in the Bronsted definition. As an acid, it can donate an H+ and becomes the conjugate base ... 

Many substances in solution have the capability of releasing or absorbing protons. According to the classic Bronsted definition, acids are those substances that release protons and bases (alkalis) are those that accept protons. Thus, acetic acid is an acid, but acetate is a base. Ammonium ion (NH4+) is an acid, whereas ammonia (NH3) is a base. When an acid loses its proton, its conjugate base is formed, whereas when a base gains protons, its conjugate acid is generated. 

The ions on the right that remain after protons depart from each of the acids are called the conjugate bases of the respective acids. The Broneted definition of an acid is very similar to the classical definition, but it includes many molecules or ions that Arrhenius would probably not have called acids. Below are listed acid reactions of water, the ammonium ion, and the hexamminecoba3t(III) ion ... 

Acid-base equilibrium — Using the Bronsted-Lowry definition (see -> acid-base theories), an acid-base reaction involves a -> proton transfer from an acid to a base. Removal of a proton from an acid forms its conjugate base, while addition of a proton to a base forms its conjugate acid. Acid-base equilibrium is achieved when the -> activity (or -> concentration) of each conjugate... 

In the Bronsted definition, an acid donates a proton and a base accepts a proton. The strengths of acids and bases are measured by the extent to which they lose or gain protons, respectively. In these reactions acids are converted to their conjugate bases and bases to their conjugate acids. Acid-base reactions go in the direction of forming the weaker acid and the weaker base. 

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