Solubility precipitates

Occlusions are minimized by maintaining the precipitate in equilibrium with its supernatant solution for an extended time. This process is called digestion and may be carried out at room temperature or at an elevated temperature. During digestion, the dynamic nature of the solubility-precipitation equilibrium, in which the precipitate dissolves and re-forms, ensures that occluded material is eventually exposed to the supernatant solution. Since the rate of dissolution and reprecipitation are slow, the chance of forming new occlusions is minimal. 

Analysis. The abiUty of silver ion to form sparingly soluble precipitates with many anions has been appHed to their quantitative deterrnination. Bromide, chloride, iodide, thiocyanate, and borate are determined by the titration of solutions containing these anions using standardized silver nitrate solutions in the presence of a suitable indicator. These titrations use fluorescein, tartrazine, rhodamine 6-G, and phenosafranine as indicators (50). 

Chemical Precipitation. If physical separation techniques do not work, separation may be achieved by chemical conversion to a soluble precipitate. 

It is preferably prepared by reacting mandelic acid ethyl ester with guanidine in boiling alcoholic solution whereby it is obtained as difficultly soluble precipitate with a yield of 90%. 

Titrations can be carried out in cases in which the solubility relations are such that potentiometric or visual indicator methods are unsatisfactory for example, when the reaction product is markedly soluble (precipitation titration) or appreciably hydrolysed (acid-base titration). This is because the readings near the equivalence point have no special significance in amperometric titrations. Readings are recorded in regions where there is excess of titrant, or of reagent, at which points the solubility or hydrolysis is suppressed by the Mass Action effect the point of intersection of these lines gives the equivalence point. 

Complexation invariably occurs by the interaction of a sparingly soluble precipitate with an excess amount of the reagent, for instance the classical example of titration between KCN and AgN03 as expressed by the following reactions ... 

The extent of process recovery is often limited by the fouling of membranes from sparing soluble precipitates. Antisealants are added during pretreatment to increase the solubility of salts likely to precipitate, enabling the membrane process to achieve a higher recovery before fouling occurs. Antisealants can be a number of polymeric substances (typically polyphosphates, phosphonates and polycarbonic acids), and as there is no treatment process to remove antisealant, they will be present in the membrane concentrate discharge. 

In consequence, A-type cations form complexes preferentially with the fluoride ion and ligands having oxygen as their electron donor atom. They are attracted to H2O more strongly than to NH3 or CN, and they do not form sulfides because OH ions readily displace HS or ions. They tend to form sparingly soluble precipitates with OH, and P04. By contrast, B-type cations coordinate... 

As described in Section VII, only chromatography is dependable for determining the (P309)3- anion quantitatively in presence of other condensed phosphates. However, since trimetaphosphate does not rapidly form a sparingly soluble precipitate with any other cation, especially in acid solution, an approximately quantitative determination is possible after precipitation of all other phosphates with barium (71, 180), provided tetrametaphosphate is not present. It can also be determined by quantitative evaluation of infrared spectra (58) and, when only crystalline substances are present, by Debye X-ray photographs (178). 

Rh en3][NO,.C10H14O]3 is prepared by treating an aqueous solution of triethylenediamino-rhodium chloride with a solution of sodium d-camphor nitronate, when a sparingly soluble precipitate of the 1-salt separates. From the mother-liquor the d-salt is obtained. These two salts serve as the starting material for the preparation of the optical isomers of the triethylenediamino-rhodium salts. 

It is likewise decomposed by various substances, metallic, nan-metallic, and organic the latter usually converting it to the state of snhchloride, It forms in- soluble, or at least but very partially soluble precipitates with albumen and fibrin. 

At the equivalence point, the titration curve is steepest for the least soluble precipitate... 

If a mixture of two ions is titrated, the less soluble precipitate forms first. If the solubilities A liquid containing suspended particles is said... 

Silver(I) halides are undoubtedly the best known of all silver(I) salts and the ability of the silver ion to form sparingly soluble precipitates with halide ions has been applied to their quantitative determination for many years. 

It has been well recognized that simple salts may drastically change solution properties of macromolecules such as solubility, precipitation temperature, viscosity, etc., and that their efficiency depends strongly on the nature of... 

Continuous dyeing of PAC-cotton plush with cationic and direct dyes by the pad steam process plays an important role. The choice of dyes must take into account liquor stability, reservation of PAC or CEL fiber, and solubility. Precipitation of cationic and anionic dyes present in the pad liquor at relatively high concentrations cannot be avoided solely by dye selection. Suitable auxiliary systems have been developed. Differently charged dyes are kept in solution separated from each other in two phases by the combination of anionic and nonionogenic surfactants. With the help of fixing accelerators, good penetration of PAC fibers can be achieved in 10-15 min with saturated steam at 98-100°C. 

Applicable to 0.15—10 mg L1 in colored or turbid waters. Iodine and bromide interfere by forming a less soluble precipitate with the silver ions. [Fe N), CrO2-, Cr2Of, and Fe3" interfere. 

It should be noted, that the miscibility gaps discussed throughout the paper are not to be confused with classical coexistence curves, i.e., the miscibility gap does not refer to the phase separation into a salt-rich and a salt-poor phase, but rather to the solubility/precipitation of the polyelectrolyte at constant Cp=0.1%. 

Due to the fact that the membranes are formed from sparingly soluble salts, adsorption or desorption on the surface can be of cation or anion, the electrode being sensitive to both species. It is also sensitive to any other ion that forms a sparingly soluble precipitate on the membrane surface. For example, the silver sulphide electrode responds to Hg2+. 

As this is an indirect method of determining the equivalence point it has some advantages. Dilute solutions can be titrated, allowing titration of sparingly soluble precipitates with no interference from supporting electrolyte. Non-electroactive compounds can be titrated so long as the titrant is electroactive, or vice versa. Titrations are fast, only three points before and three points after the equivalent point being necessary. 

If catalysts are prepared by coprecipitation, the relative solubilities of the precipitates and the possibility for the formation of defined mixed phases are essential. If one of the components is much more soluble than the other, there is a possibility that sequential precipitation occurs. This leads to concentration gradients in the product and less intimate mixing of the components. If this effect is not compensated by adsorption or occlusion of the more soluble component, the precipitation should be carried out at high supersaturation in order to exceed the solubility product for both components simultaneously. Precipitation of the less soluble product will proceed slightly faster, and the initially formed particles can act as nucleation sites for the more soluble precipitate which forms by heterogeneous precipitation. The problem is less crucial if both components form a defined, insoluble species. This is for instance the case for the coprecipitation of nickel and aluminum which can form defined compounds of the hydrotalcite type (see the extensive review by Cavani et al. [9] and the summary by Andrew [10]). 

Mercury(II) sulphide is one of the least soluble precipitates known (Ks = 4x 10"54). 

Example 5.5 With the following data, establish the four main equilibrium equations involved in the solubility/precipitation of iron (III) hydroxide, in the form log [X] =/(pH). Then, plot the complete solubility diagram for this substance. Lastly, show the predominance zone of the insoluble Fe(OH)3. 

Precipitation is the formation of a compound that exceeds its solubility limit in a given medium. Coprecipitation is the inclusion or trapping of an otherwise soluble compound when a precipitate is formed under the same conditions. Precipitation calculations, including equilibrium diagrams involving the solubility-precipitation of solids, are discussed in Section 5.3. 

There is one property of the chalcogenocyanate complexes which may temporarily outweigh strictly kinetic or thermodynamic factors, namely, solubility. Precipitation of the less soluble of a pair of linkage isomers may give a false impression as to which is the stable compound. However, such is the wealth of compounds prepared, the majority of the structures may be regarded as the thermodynamically stable forms. This assumption is often supported by evidence concerning the relative stabilities of linkage isomers. 

In summary, the mean of solubility, precipitation, and calorimetric data for kaolinite free of particle size effects yields the value for the free energy of formation of -907.7 +0.4 kcal/mol. 

Fmoc-Val-OH (0.339 g, 1 mmol) in CHjCh (5 mL) was refluxed under Nj with cyanuric fluoride (700 pL, 8 mmol) and pyridine (81 pL, 1 mmol) for 2 h. The mixture, from which a white water-soluble precipitate had settled, was extracted with ice water (2xl5mL). Removal of the solvent from the dry (MgS04) organic layer gave a white solid which was recrystallized (CH2CI2/hexane) to give the pure add fluoride yield 239mg (70%) mp 113-114 C. 

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