Solubility precipitation reactions

A precipitation reaction occurs when two or more soluble species combine to form an insoluble product that we call a precipitate. The most common precipitation reaction is a metathesis reaction, in which two soluble ionic compounds exchange parts. When a solution of lead nitrate is added to a solution of potassium chloride, for example, a precipitate of lead chloride forms. We usually write the balanced reaction as a net ionic equation, in which only the precipitate and those ions involved in the reaction are included. Thus, the precipitation of PbCl2 is written as... 

The most important types of reactions are precipitation reactions, acid-base reactions, metal-ligand complexation reactions, and redox reactions. In a precipitation reaction two or more soluble species combine to produce an insoluble product called a precipitate. The equilibrium properties of a precipitation reaction are described by a solubility product. 

Solubility losses are minimized by carefully controlling the composition of the solution in which the precipitate forms. This, in turn, requires an understanding of the relevant equilibrium reactions affecting the precipitate s solubility. Eor example, Ag+ can be determined gravimetrically by adding Ch as a precipitant, forming a precipitate of AgCl. 

If this is the only reaction considered, we would falsely conclude that the precipitate s solubility, SAgcb is given by... 

Another important parameter that may affect a precipitate s solubility is the pH of the solution in which the precipitate forms. For example, hydroxide precipitates, such as Fe(OH)3, are more soluble at lower pH levels at which the concentration of OH is small. The effect of pH on solubility is not limited to hydroxide precipitates, but also affects precipitates containing basic or acidic ions. The solubility of Ca3(P04)2 is pH-dependent because phosphate is a weak base. The following four reactions, therefore, govern the solubility of Ca3(P04)2. 

Solid Compounds. The tripositive actinide ions resemble tripositive lanthanide ions in their precipitation reactions (13,14,17,20,22). Tetrapositive actinide ions are similar in this respect to Ce . Thus the duorides and oxalates are insoluble in acid solution, and the nitrates, sulfates, perchlorates, and sulfides are all soluble. The tetrapositive actinide ions form insoluble iodates and various substituted arsenates even in rather strongly acid solution. The MO2 actinide ions can be precipitated as the potassium salt from strong carbonate solutions. In solutions containing a high concentration of sodium and acetate ions, the actinide ions form the insoluble crystalline salt NaM02(02CCH2)3. The hydroxides of all four ionic types are insoluble ... 

Note that the brackets, [ ], refer to the concentration of the species. K,p is the solubility product constant hence [Cu " ] and [OH] are equal to the molar concentrations of copper and hydroxyl ions, respectively. The K p is commonly used in determining suitable precipitation reactions for removal of ionic species from solution. In the same example, the pH for removal of copper to any specified concentration can be determined by substituting the molar concentration into the following equation ... 

Soluble sulfides (i.e., H S, HS" and S ", with sulfur at minus two oxidation state) are chemically very reactive. The two general types of soluble-sulfide reactions may be identified as precipitation reaction (type A) and redox reaction (type B). 

In type A reaction soluble sulfide ions combine with metal ions to form a precipitate of insoluble metal sulfide. Sulfur s oxidation state of minus two does not change in this reaction. The reaction is... 

Both possible products are soluble, so there is no precipitation reaction and no equation. 

Use Figures 10-5 and 10-6 or Table 10-1 to decide which of the following soluble salts would permit a separation of magnesium and lead through a precipitation reaction sodium iodide, Nal sodium sulfide, Na2S sodium carbonate, Na2C03. 

The standard potential e of reaction (1) is 0.56 volt and of reaction (2) 0.60 volt. By suitably controlling the experimental conditions (e.g. by the addition of barium ions, which form the sparingly soluble barium manganate as a fine, granular precipitate), reaction (1) occurs almost exclusively. In moderately alkaline solutions permanganate is reduced quantitatively to manganese dioxide. The half-cell reaction is ... 

The precipitate is soluble in free mineral acids (even as little as is liberated by reaction in neutral solution), in solutions containing more than 50 per cent of ethanol by volume, in hot water (0.6 mg per 100 mL), and in concentrated ammoniacal solutions of cobalt salts, but is insoluble in dilute ammonia solution, in solutions of ammonium salts, and in dilute acetic (ethanoic) acid-sodium acetate solutions. Large amounts of aqueous ammonia and of cobalt, zinc, or copper retard the precipitation extra reagent must be added, for these elements consume dimethylglyoxime to form various soluble compounds. Better results are obtained in the presence of cobalt, manganese, or zinc by adding sodium or ammonium acetate to precipitate the complex iron(III), aluminium, and chromium(III) must, however, be absent. 

The reaction mixture is cooled, diluted with 100 mL of sat. aq NaCI and extracted with four 50-mL portions of Ei,0. The combined ethereal extracts are washed with 50 ml. of sat. aq NaCI, dried, filtered and concentrated to a volume of a few milliliters. 20 ntL of petroleum ether arc added to precipitate the soluble salts. The mixture is filtered through a silica gel column (petroleum ether)and purified by medium-pressure liquid chromatography yield 360 mg (65%). 

The calcium phosphate solubility constant [KCa3(P04)2] is extremely small and phosphate quickly reacts with calcium when present in warm to hot, alkaline BW in the ortho- form. This reaction is complete and superior to the soda ash precipitation reaction. In addition, calcium phosphate is stable and does not decompose. 

Table 1.1 summarizes the solubility patterns of common ionic compounds in water. Notice that all nitrates and all common compounds of the Group 1 metals are soluble so they make useful starting solutions for precipitation reactions. Any spectator ions can be used, provided that they remain in solution and do not otherwise react. For example, Table 1.1 shows that mercury(I) iodide, Hg2I2, is insoluble. It is formed as a precipitate when solutions containing Hg22+ ions and I ions are mixed ... 

The solubility rules in Table 1.1 are used to predict the outcomes of precipitation reactions. 

How would you use the solubility rules in Table 1.1 to separate the following pairs of ions In each case indicate what reagent you would add and write the net ionic equation for the precipitation reaction (a) lead(II) and copper(II) ions ... 

Americium will occur in soil in the trivalent state. The transformations that may occur would involve complexation with inorganic and organic ligands (see Section 6.3.1) and precipitation reactions with anions and other substances present in the soil solution. The 241 Am occurring as an ingrowth progeny of 241Pu and trapped in a plutonium matrix will exhibit solubility and biokinetic characteristics of the plutonium, rather than americium. 

Species with low solubility in water may exist in solid form (e.g., Ag2S, BaS()4) or liquid form (e.g., chlorinated solvents). Precipitation reactions and immiscible-phase separation are important processes affecting this type of speciation. 

This is a precipitation reaction, since one product, FeP04, is not soluble. 

The solubility of components in the soil solution will be controlled by the innate solubility of the compound in question and the existing soil solution characteristics, particularly salts already present. High salt concentrations will result in salting out and precipitation of some components. Note here that salt concentration is not constant in that as the soil dries, the concentration of salt increases. Precipitation reactions may not be reversible when the soil water content is subsequently increased. 

Precipitation reactions involve the formation of an insoluble compound, a precipitate, from the mixing of two aqueous solutions containing soluble compounds. To predict if precipitation will occur upon the mixing of two solutions, you must know and be able to apply the following solubility rules. You should apply these rules to all combination of cations with anions in each of the mixed solutions. 

The Ostwald Step Rule, or the rule of stages postulates that the precipitate with the highest solubility, i.e., the least stable solid phase will form first in a consecutive precipitation reaction. This rule is very well documented mineral formation via precursors and intermediates can be explained by the kinetics of the nucleation process. The precipitation sequence results because the nucleation of a more soluble... 

Precipitation reactions form an insoluble compound, a precipitate, from the mixing of two soluble compounds. 

In the precipitation reaction involving chloride and silver nitrate, the addition of even a small quantity of the latter shall effect precipitation of AgCl provided that Ksp has been exceeded significantly. At this juncture, the concentrations of both Ag+ and Cl are related by the solubility-product equilibrium constant thus, we have ... 

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