Proton donor, acid

The water equilibrium illustrates the amphiprotic nature of H2 O. In this reaction, one water molecule acts as a proton donor (acid), and another acts as a proton acceptor (base). 

This is known as specific add catalysis, specific in that H30 is the only acidic species that catalyses the reaction the reaction rate is found to be unaffected by the addition of other potential proton donors (acids) such as NH4 , provided that [H3Offi], i.e. pH, is not changed, indirectly, by their addition. The mechanism of the above acetal hydrolysis is believed to be,... 

Amino groups may act not only as proton acceptor, but also as proton donor. Acidic N—H protons interact with basic solvents. In these cases an ortho-nitro group in an aniline system competes with the solvent by an internal hydrogen bond66, as depicted in 12. The stretching frequencies (by IR spectra in carbon tetrachloride) of vnh of complexes between A-methylaniline or diphenylamine (and some nitro-anilines66) and solvents depend on the proton accepting ability of the solvent (which is a moderate base)67. The frequency shifts are linearly related to the solvent s donor number (DN)3. 

In 1923, Johannes Br nsted and his English counterpart Thomas Lowry independently developed a more general acid-base theory. According to the Br nsted-Lowry model, an acid is a proton (H+) donor and a base is a proton acceptor. Each proton donor (acid) has its pair (conjugate) proton acceptor (base). In an acid-base reaction, H (proton) is transferred from an acid to a base. For example ... 

In the case of water, however, the concentration of either the OH- or H+ ions can be decreased by adding proton donors (acids) or proton acceptors (bases). Thus, a proton donor releases hydrogen ions into the solution (i.e., increases), and the only way the product Kw (i.e., COH-CH+) remains a constant is by a decrease in ( OH ... 

Proton donors (acids) t-BuCT/pH-glass electrode... 

In the reverse reaction, H30+ acts as the proton donor (acid) and A- acts as the proton acceptor (base). Typical examples of Bronsted-Lowry acids include not only electrically neutral molecules, such as HC1, HN03, and HF, but also cations and anions of salts that contain transferable protons, such as NH4+, HS04 , and HC03-. 

To predict the direction of reaction, use the balanced equation to identify the proton donors (acids) and proton acceptors (bases), and then use Table 15.1 to identify the stronger acid and the stronger base. When equal concentrations of reactants and products are present, proton transfer always occurs from the stronger acid to the stronger base. 

The number of moles of hydrogen ion equivalent to the excess of proton acceptors (bases formed from weak acids with a dissociation constant K < 10 at 25 °C and zero ionic strength) over the proton donors (acids with K > 10 ) in one kilogram of sample. 

Along with the Bronsted-Low ery concept of a proton donor (acid) and a... 

Simple bases such as NaOH and KOH act as sources of OH (aq) in aqueous solution. The OH (aq) ion is a base because it can accept a proton from a proton donor acid, H20(l), in aqueous solution. 

The acid and base of a half-reaction are called conjugate pairs. Free protons do not exist in solution, and there must be a proton acceptor (base) before a proton donor (acid) will release its proton. That is, there must be a combination of two half-reactions. Some acid-base reactions in different solvents are illustrated in Table 7.1. In the first example, acetate ion is the conjugate base of acetic acid and ammonium ion is the conjugate acid of ammonia. The first four examples represent ionization of an acid or a base in a solvent, while the others represent a neutralization reaction between an acid and a base in the solvent. 

Solvents can be grouped on the basis of their properties as proton donors (acidic), proton acceptors (basic), and dipole interactions. Solvents can be positioned within the Solvent Selectivity Triangle (Fig. 17) on the basis of the relative involvement of each of these three factors as parameters of solubility. Mobile phases consisting of a mixture of three solvents can be optimized by... 

Ka for HP04 is 4.8 x 10 Note that HP04 is the conjngate base of H2PO4, so Kb is 1.6 x 10 Comparing the two A s, we conclnde that the monohydrogen phosphate ion is a much stronger proton acceptor (base) than a proton donor (acid). The solntion will be basic. 

One or two examples of the use of these concepts will illustrate the ideas and help to formulate appropriate rate equations. The acidic catalysts, such as silica-alumina, can apparently act as Lewis (electron acceptor) or Br0nsted (proton donor) acids, and thus form some sort of carbonium ion from hydrocarbons, for example. Note the analogy between this hydrogen deficient entity and a free radical. However, the somewhat different rules for the reactions of carbonium ions apply from organic chemistry and permit miquantitative predictions of the products expected see Table 2.1-2 from Oblad, et al. [11 ]. 

Bronsted superacids Proton donor acids stronger than 100% sulfuric acid. 

Conjugate Bronsted-Lewis superacids Superacidic proton donor acids comprised of a combination of Bronsted and Lewis acids. 

Hammet s acidity constant, Hq A logarithmic thermodynamic scale used to relate acidity of proton donor acids. 

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