Dissociation, of acids

Numerous measurements of the conductivity of aqueous solutions performed by the school of Friedrich Kohhansch (1840-1910) and the investigations of Jacobns van t Hoff (1852-1911 Nobel prize, 1901) on the osmotic pressure of solutions led the young Swedish physicist Svante August Arrhenius (1859-1927 Nobel prize, 1903) to establish in 1884 in his thesis the main ideas of his famous theory of electrolytic dissociation of acids, alkalis, and salts in solutions. Despite the sceptitism of some chemists, this theory was generally accepted toward the end of the centnry. 

Males et al. [103] used aqueous mobile phase with formic acid for the separation of flavonoids and phenolic acids in the extract of Sambuci flos. In a cited paper, authors listed ten mobile phases with addition of acids used by other investigators for chromatography of polyphenolic material. For micropreparative separation and isolation of antraquinone derivatives (aloine and aloeemodine) from the hardened sap of aloe (Liliaceae family), Wawrzynowicz et al. used 0.5-mm silica precoated plates and isopropanol-methanol-acetic acid as the mobile phase [104]. The addition of small amounts of acid to the mobile phase suppressed the dissociation of acidic groups (phenolic, carboxylic) and thus prevented band diffusions. 

The theory of electrolysis is continued with one additional example in which a solution of hydrochloric acid contained in a container is considered. The dissociation of acid will cause the solution to have chlorine and hydrogen ions. It is shown below ... 

The surface charge of a fibre has an important influence on its interaction with chemicals (both particulate and soluble) which are added to the aqueous fibre suspension. Their anionicity gives them a high affinity towards cationic additives, and many additives are produced in a cationic form in order to maximise their retention. The pH of the aqueous paper-making system is also important in these interactions. The surface charge of cellulose, because it arises from the dissociation of acidic groups, is dependent upon pH (see... 

Once precipitation begins, a quasi-steady state will eventually be attained in which the soil pe and pH are poised by the redox and precipitation equilibria operating. In the transition to the steady state, protons will be provided by dissociation of acids in the soil solution—e.g. H2CO3 derived from C02-and by reactions with the soil exchange complex. The course of reduction and the eventual steady state will depend on these reactions and it is therefore necessary to allow for them in predicting what the steady state conditions will be. 

Figure 6. Experimental data on the effect of pK and degree of dissociation of acids and bases on their reverse osmosis separations in systems involving dilute aqueous solutions and cellulose acetate membranes ( 5, 16, 17,1...

Aa > 0.8, the dissociation of acid groups (which are diluted by the reaction) increases and Ch+ becomes almost proportional to C. Third-order kinetics are then observed. 

Strong acid (see p 342). Because of complete dissociation of acid in dilute solution,... 

Exercise 26-37 Would you expect a Hammett type of relationship to correlate data for the dissociation of acids of the following type with rate data for hydrolysis of the corresponding esters Explain. 

Bassam Z. Shakhashiri, "Coni ductivity and Extent of Dissociation of Acids in Aqueous Solution," Chemical Demonstrations, A Handbook for Teachers of Chemistry, Vol. 3 (The University of Wisconsin Press, Madison, 1989) pp. 140-145. Universal indicator and a conductivity probe are used to explore the relative acidity and conductivity of a series of aqueous acids. 

Biological surfaces, as well as metal oxides, acquire an electrostatic charge in water through the dissociation of acidic or basic groups which lie near the solid/ aqueous interface. As two such surfaces, separated by an aqueous electrolyte, are brought together the volume between them decreases and consequently the counterion concentration of the solution must tend to increase in order to preserve overall electro-... 

The traditional theory could not explain the above observations. In recent papers concerned with monovalent electrolytes,4,5 the restabilization was attributed to the following two effects (i) the reassociation of charges on the surface and their replacement by ion pairs (surface dipoles), and (ii) the fields generated by the surface dipoles and in the bulk by neighboring dipoles. While the surface charge density formed through the dissociation of acidic and basic sites is decreased by the adsorption of counterions, the charges are replaced by ion pairs (dipoles) which polarize the water molecules nearby. This polar-... 

Since Figure 2.3 represents how equilibrium constants are calculated and since we are specifically studying dissociation of acids, can be redefined for acids as the acid dissociation constant (K.t) illustrated in Figure 2.4. 

The higher dielectric constant of NMA, compared to water, might be expected to promote dissociation of acids but studies in other nonaqueous solvents and in mixed solvents indicate that the dielectric constant is seldom the predominant factor controlling acid dissociation processes199). Instead, whether a particular acid is stronger in one solvent or another, will likely be quite dependent on the relative solvation of the acid, of the proton and of the conjugate base in the two solvents. 

Reactions (i) to (iv) represent dissociations of acids, reaction (v) is the common reaction, called neutralization , of strong acids with strong bases, reaction (vi) describes the neutralization reaction between acetic acid and ammonia which takes place in the absence of water, reactions (vii) to (ix) represent hydrolysis reactions, while reaction (x), which is the same as reaction (v) but in the opposite direction, describes the dissociation (or, more properly, the autoprotolysis) of water. Some of these reactions will be discussed in more detail in subsequent chapters. 

This statement has its limitations. Ionic polymerization in hydrocarbons is always kinetically complicated, it often starts only after the addition of a polar compound (co-initiator), and it is affected by the aggregation of initiating and propagating particles. In strongly polar media, activation of initiator by dissociation of acids and bases is easy. Such solvent is simultaneously a reactive transfer agent. Propagation usually does not occur, and only low molecular products are formed. Exceptions can, of course, be found. During anionic polymerization of lactams in DMF, the solvent only increases the amount of dissociated initiator [27]. 

Consider two parallel planar similar ion-penetrable membranes 1 and 2 at separation h immersed in a solution containing a symmetrical electrolyte of valence z and bulk concentration n [12]. We take an x-axis as shown in Fig. 13.2. The surface is in equilibrium with a monovalent electrolyte solution of bulk concentration n. Note here that n represents the total concentration of monovalent cations including H" " ions and that of monovalent anions including OH ions. Let hh be the H" " concentration in the bulk solution phase. In the membrane phase, monovalent acidic groups of dissociation constant are distributed at a density max- The mass action law for the dissociation of acidic groups AH (AH A + H" ") gives the number density N x) of dissociated groups at position x in... 

Many handbooks list dissociation constants (the equilibrium constant for the dissociation of acid into a proton and its conjugate base) as pKa s. 

M. Buonsanto. Boll. soc. ital. biol. sper. 27, 225-8 (1951). Cryoscopy dissociation of acids, alcohols by ultrasonics. 

The effects of solution acidity and basicity on luminescence spectra result from the dissociation of acidic functional groups or protonation of basic functional groups associated with the aromatic portions of fluorescing and phosphorescing molecules. Protonation or dissociation can alter the natures and rates of non-radiative processes competing with luminescence and, thereby, affect the quantum yields of emission. For example, the antimalarial mefloquine fluoresces very weakly but phosphoresces well in neutral aqueous media. However, at pH < 1, its protonated form fluoresces intensely, and its phosphorescence is very weak. 

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