Undissociated

Addition of excess H ions to this solution will cause the equilibrium to move towards undissociated acid thereby decreasing the concentration of Ac . This effect is known as the common-ion effect and is of considerable practical importance. Thus, e.g. in the precipitation of metal ions as insoluble sulphides. 

However because of the equilibrium between the solid and dissolved undissociated AB, the concentration of the latter may be considered to remain constant and hence... 

Results can sometimes be unexpected. The first study of this type made use of labeled Aerosol OTN [111], an anionic surfactant, also known as di-n-octylsodium sulfosuccinate. The measured F was twice that in Eq. III-93 and it was realized that hydrolysis had occurred, that is, X + H2O = HX + OH , and that it was the undissociated acid HX that was surface-active. Since pH was essentially constant, the activity of HX was just proportional to C. A similar behavior was found for aqueous sodium stearate [112]. 

Ionic conductors arise whenever there are mobile ions present. In electrolyte solutions, such ions are nonually fonued by the dissolution of an ionic solid. Provided the dissolution leads to the complete separation of the ionic components to fonu essentially independent anions and cations, the electrolyte is tenued strong. By contrast, weak electrolytes, such as organic carboxylic acids, are present mainly in the undissociated fonu in solution, with the total ionic concentration orders of magnitude lower than the fonual concentration of the solute. Ionic conductivity will be treated in some detail below, but we initially concentrate on the equilibrium stmcture of liquids and ionic solutions. 

Spectra of two different bands of (1TF)2, showing the difference between predissociated and undissociated spectra [21], are shown in figure Cl. 3.5... 

The amount of carbonic acid present, undissociated or dissociated, is only about 1 of the total concentration of dissolved carbon dioxide. Carbonic acid, in l especi of its dissociation into hydrogen and hydrogencarbonate ions, is actually a stronger acid than acetic acid the dissociation constant is ... 

The role of the quaternization of the azasubstituent in the nucleophilic substitution at 2-halogenothiazoles is in fact emphasized by the reactivity of 2-halogenothiazoles with undissociated thiophenol (35), which proceeds faster than the corresponding reaction of 2-halogenothiazoles with thiophenolate anion, through the pathways shown in Scheme 6. Moreover, the 4-halogenothiazoles do not react with undissociated thiophenols, while the 5-halogenothiazoles react well (48). 

Writing the equation in the usual way directs too much attention to the atoms and not enough to the electrons We can remedy that by deleting any spec tator ions and by showing the unshared electron pairs and covalent bonds that are made and broken Both sodium hydroxide and sodium fluoride are com pletely ionized in water therefore Na" which ap pears on both sides of the equation is a spectator ion Hydrogen fluoride is a weak acid and exists as undissociated HF molecules in water... 

For substances that ionize in solution, such as NaCl, molarity and formality are different. For example, dissolving 0.1 mol of NaCl in 1 L of water gives a solution containing 0.1 mol of Na and 0.1 mol of Ch. The molarity of NaCl, therefore, is zero since there is essentially no undissociated NaCl in solution. The solution. 

Weak acids, of which aqueous acetic acid is one example, cannot completely donate their acidic protons to the solvent. Instead, most of the acid remains undissociated, with only a small fraction present as the conjugate base. 

Ionic polymers may exist as undissociated, unsolvated ion pairs undissociated ion pairs solvated to some extent solvated ions dissociated to some extent or some combination of these. The propagation rate constant kp and the dissociation equilibrium constant K of the lithium salt of anionic... 

The corresponding oxygen s curves in Figure 8.20 support these conclusions. The peak at about 529 eV is due to oxygen atoms but a peak at about 530.5 eX due to undissociated NO, is not as well resolved as for the nitrogen lx peaks. 

The phenomenon of multiphoton dissociation finds a possible application in the separation of isotopes. For this purpose it is not only the high power of the laser that is important but the fact that it is highly monochromatic. This latter property makes it possible, in favourable circumstances, for the laser radiation to be absorbed selectively by a single isotopic molecular species. This species is then selectively dissociated resulting in isotopic enrichment both in the dissociation products and in the undissociated material. 

Whereas the linear distribution law can be appHed to the undissociated monomer, the interfacial distribution of total benzoic acid, as determined by analysis, is nonlinear. 

The equihbrium constant for this reaction is ca 1.022 at 100°C. The B concentrates in the Hquid phase (23). However, the vapor phase contains ca 40% undissociated complex, which lowers the effective single-stage separation factor to ca 1.014. 

Cyanic acid (HOCN) reacts slowly, whereas undissociated HCN and HNO2 do not react at all (39). 

The aqueous solubility of ammonia decreases rapidly as temperature increases. The existence of undissociated ammonium hydroxide [1336-21 -6] NH OH,... 

The inhibitory activity of sorbates is attributed to the undissociated acid molecule. The activity, therefore, depends on the pH of the substrate. The upper limit for activity is approximately pH 6.5 in moist appHcations the degree of activity increases as the pH decreases. The upper pH limit can be increased in low water activity systems. The following indicates the effect of pH on the dissociation of sorbic acid, ie, percentage of undissociated sorbic acid at various pH levels (76,77). 

Sodium and potassium benzoate are employed in a wide range of preservative appHcations because they provide an effective combination of antimicrobial action, low cost, and safety. Although sodium and potassium benzoate are the preservatives offered in the marketplace, the actual active ingredient being sold is free (or undissociated) benzoic acid. The benzoate ion has essentially no antimicrobial properties. Since it is the undissociated (free) benzoic acid that provides the antimicrobial action, sodium benzoate and potassium benzoate are recommended for use in appHcation areas where the pH is at 4.5 or lower (Table 8). 

In solutions, the concentration of available chlorine in the form of hypochlorite or hypochlorous acid is called free-available chlorine. The available chlorine in the form of undissociated A/-chloro compounds is called combined-available chlorine. Several analytical methods can be used to distinguish between free- and combined-available chlorine (8). Bleaches that do not form hypochlorite in solution like chlorine dioxide and nonchlorine bleaches can be characterized by thek equivalent available chlorine content. This can be calculated from equation 5 by substituting the number of electrons accepted divided by two for the number of active chlorine atoms. It can also be measured by iodomettic titration. 

Hydrogen peroxide is a very weak acid and in aqueous solutions only dissociates slightly (eq. 14) = 1.78 x 10 . Undissociated hydrogen... 

Dilute aqueous solutions of boric acid contain predorninantly monomeric, undissociated B(OH)3 molecules. The acidic properties of boric acid ... 

Chlorine atoms obtained from the dissociation of chlorine molecules by thermal, photochemical, or chemically initiated processes react with a methane molecule to form hydrogen chloride and a methyl-free radical. The methyl radical reacts with an undissociated chlorine molecule to give methyl chloride and a new chlorine radical necessary to continue the reaction. Other more highly chlorinated products are formed in a similar manner. Chain terrnination may proceed by way of several of the examples cited in equations 6, 7, and 8. The initial radical-producing catalytic process is inhibited by oxygen to an extent that only a few ppm of oxygen can drastically decrease the reaction rate. In some commercial processes, small amounts of air are dehberately added to inhibit chlorination beyond the monochloro stage. 

Dimerization involves addition of the cyanamide anion to the nitnle group of an undissociated molecule to give the anion of cyanoguanidine, or dicyandiamide. This reaction takes place most readily at pH 8—10 where the reactants are present in favorable proportion. The product is a weaker acid than cyanamide and is protonated at once with generation of a new cyanamide anion. 

Organic acids may inhibit growth when present in the undissociated form because of their abiHty to change the pH inside the ceU. The most efficient are benzoic acid and sorbic acid, but formic, acetic, and propionic acid also have this effect. The parabens, ie, -hydroxy benzoic acid esters, are also used because of their antimicrobial effect over a broad pH range. 

It will be noted that pyrrole-3-carboxylic acid (154) is an appreciably weaker acid than benzoic acid and this is attributed to the stabilization of the undissociated acid by electron release from nitrogen. The 2-carboxylic acids of furan, thiophene, selenophene and tel-lurophene are all stronger acids than benzoic acid, tellurophene-2-carboxylic acid (pisTa 4.0) being the weakest acid in this series (77AHC(21)119). 

Hydrogen sulfide is a commonly occurring decomposition product of organic matter. It is relatively water soluble at higher pHs where it is predominantly dissociated as and S ions. As the pH is decreased below 7, undissociated gas HjS begins to predominate and is released. Since its vapor density is > 1.0, HjS gas tends to settle in low places and creates a toxicity hazard. H S is readily oxidizable by a number of means to less toxic SO3" or 804 forms. 

---