Precipitation ionization equilibrium

EXAMPLE 18-8 Determining Whether a Precipitate Will Form in a Solution in Which There Is Also an Ionization Equilibrium... 

The protonation reactions for ionizable molecules have been defined in Section 3.1. When a solute molecule, HA (or B), is in equilibrium with its precipitated form, HA(s) (or B(s)), the process is denoted by the equilibrium expression... 

On the basis of surface and bulk interaction with water. Small [85] classified bile acids as insoluble amphiphiles and bile salts as soluble amphiphiles. On account of the undissociated carboxylic acid group, the aqueous solubility of bile acids is limited [35] in contrast, many bile salts have high aqueous solubilities as monomers [33] and, in addition, their aqueous solubilities are greatly enhanced by the formation of micelles [5,6]. Because many bile salts are weak electrolytes, their ionization and solubility properties are more complicated than those of simple inorganic or organic electrolytes [5,35]. For example, the p/Tj, values of bile acids in water vary markedly as functions of bile salt concentration and, because micelles formed by the A (anionic) species can solubilize the HA (acid) species [5,35], the equilibrium precipitation pH values of bile acids also vary as functions of bile salt concentration. Finally, certain bile salts are characterized by insolubility at ambient temperatures [2,5,6,86,87], only becoming soluble as micelles at elevated temperatures (the critical micellar temperature) [6]. 

Discussion The hydroxides of most of the bivalent metals which are precipitated by a solution of ammonium hydroxide are not precipitated by this reagent if an ammonium salt is present in the solution. The extent of the ionization of ammonium hydroxide is small and when an ammonium salt is added to the solution the ionization of the hydroxide is reduced as the result of the presence of the added ammonium ions. Such an addition forces the equilibrium represented by the equation... 

The most oxidized species, CO2, exists in the atmosphere as a gas whose concentration far exceeds that of other carbon-containing substances. In water, it takes part in a series of equilibrium reactions involving hydration, ionization, and precipitation ... 

A new method that avoids the difficulties related to phase separation has been recently proposed to measure the solubility of ionizable compounds. - The method is based on potentiometric titration, and the separation between precipitate and solute is obtained through the selectivity of the pH-electrode. To summarize, the principle of the method is that only the dissolved substance participates to the protonation-deprotonation equilibrium. 

In Section 12.1, we discussed the effect of a common ion on acid and base ionizations. Here we will examine the relationship between the common ion effect and solubility. As we have noted, the solubihty product is an equilibrium constant precipitation of an ionic compound from solution occurs whenever the ion product exceeds for that substance. In a saturated solution of AgCl, for example, the ion product [Ag ][Cr] is, of course, equal to K p. Furthermore, simple stoichiometry tells us that [Ag ] = [Cl ]. But this equality does not hold in all situations. 

Strongly electrophilic species can also be generated by shifting the equilibrium of ionization through the precipitation of a salt, like in the following example ... 

---