Acid-base equilibria cation reaction with water

Determine whether the cation is from a strong or weak base, and whether the anion is from a strong or weak acid. Ions derived from weak bases or weak acids react with water and affect the pH of the solution. If both ions react with water, compare the equilibrium constants K and Aib) to determine which reaction goes farthest to completion. 

I. Salts of strong acids and strong bases, when dissolved in water, show a neutral reaction, as neither the anion nor the cation combines with hydrogen or hydroxyl ions respectively to form sparingly dissociated products. The dissociation equilibrium of water... 

On the other hand, if HA is an uncharged acid z = — V, e.g. CH3—CO2H), the right-hand side of Eq. (4-10) involves the sum of two reciprocal radii (zha = 0) and a strong influence of the relative permittivity on the ionization equilibrium is expected. Because in acid/base reactions of this charge type, neutral molecules are converted into anions and cations, which attract each other, reaction (4-5) will shift to the right with an increase in relative permittivity of the solvent in which HA is dissolved. Ionization increases when increases. This rule is qualitatively verifiable for water and alcohols as... 

However, the case in which the solubility of a solid can be calculated from the known analytical concentration of added components and from the solubility product alone is very seldom encountered. Ions that have dissolved from a crystalline lattice frequently undergo chemical reactions in solution, and therefore other equilibria in addition to the solubility product have to be considered. The reaction of the salt cation or anion with water to undergo acid-base reactions is very common. Furthermore, complex formation of salt cation and salt anion with each other and with one of the constituents of the solution has to be considered. For example, the solubility of FeS(s) in a sulfide-containing aqueous solution depends on, in addition to the solubility equilibrium, acid-base equilibria of the cation (e.g., Fe + H2O = FeOH + H ) and of the anion (e.g., S + HjO = HS + OH, and HS" + H2O = H2S + OH ), as well as on equilibria describing complex formation (e.g., formation of FeHS" or FeSi ). 

Water doesn t have to be one of the participants—if we replace water in the reaction we have been discussing with ammonia, we now have ammonia as the conjugate base of NH (the ammonium cation) and the ammonium cation as the conjugate acid of ammonia. What is different is the position of equilibrium ammonia is more basic than water and now the equilibrium will be well over to the right. As you will see, piC will help us assess where equilibria like these lie. 

A strong acid is released during the reaction. An important point to note is that the formed oxime does not exhibit any basic character also, the initial solution was neutral. This is easily explained by the fact that hydroxylamine is a strong base and, hence, its conjugate acid a very weak one. It is interesting also to note that the reaction medium is nonaqueous for the most part, since it only contains 10% water (in mass). Water is added essentially in order to dissolve the hydroxylamine hydrochloride. The medium also contains pyridine in order to displace the oxime formation equilibrium toward the right by formation of the pyridinium ion. The hydrochloric acid released is titrated with a methanolic sodium hydroxide solution. The indicator chosen is bromophenol blue, whose color-change interval is located on the acidic side. Actually, it is the pyridinium cation that is titrated with the methanolic sodium hydroxide solution. The pyridinium cation results from the protonation of the pyridine by the released hydrochloric acid. 

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