Solubility precipitation calculations

The AgaEDTA salt was obtained by adding AgNC>3 to Ag EDTA3" or EDTA4-, keeping the pH of the solution above 8. The precipitate was silk white and appeared as fine needles under a microscope (X200). Its solubility was calculated to be between 1.9 and 2.8 x 10-4M.422... 

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. 

In a wet atmosphere, iron and steel corrode producing first hydrated ferrous ions at the anodic site and hydrated hydroxide ions, OHaq, at the cathodic site where air-oxygen is reduced into OHaq ions. The presence of salts such as NaCl is known to enhance corrosion. Hydrated ferrous ions occur in the form of Fe2+, Fe(OH)+, Fe(OH) aq, and Fe(OH) aq. Gel-like hydroxide of Fe(OH)2,solid precipitates when the concentration of hydrated ferrous ions exceeds its solubility. Thermodynamic calculation gives the proton level to be pH 9.31 and 1.27 x 10 5 mol dm 3 of solubility at which the equilibrium is established between gel-like Fe(OH)2,soiid and hydrated OHaq ions when Fe(OH)2solid is put in pure water [90]. 

Because of the large scatter of solubility data for amorphous Th(lV) precipitates, this review did not cany out temperature corrections for the hydrolysis constants used and the solubility constant calculated from the data at 17°C [1964NAB/KUD] are compared to the standard state temperature of 298.15 K (25°C). 

Figure A-45 Experimental data determined in [2000BUN/1CNO], [2003NEC/ALT] for TI1O2 colloids using the titration-LlBD method. The solubility from oversaturation after precipitation of microciystalline Th02(cr, hyd) and from imdersaturation with crystalline Th02(cr) are compared to the solubility curves calculated for Th02(cr) and Th(OH)4(am) (from [2003NEC/ALT]).

The laboratory studies were designed to examine in detail the composition of aluminum species in dilute solutions having values of r between 0.5 and 4.0, after various periods of aging. The behavior of OH boimd to aluminum was examined by kinetic methods, precipitated solids were identified by the electron microscope and x-ray diffractometer, and equilibrium solubilities were calculated for stable and metastable aluminum hydroxides. 

Example 2 Yield from Evaporative Cooling Starting with 1000 lb of water in a solution at H on the solubility diagram in Fig. 18-57, calculate the yield on evaporative cooling and concentrate the solution back to point H so the cycle can be repeated, indicating the amount of NaCl precipitated and the evaporation and dilution required at the different steps in the process. 

In solving problems of this type, it is convenient to list the material balance and the solubility ratios. The various points on the material balance are calculated by multiplying the quantity of the component which does not precipitate from solution during the transition from one point to another (normally the... 

A colorless, colloidal precipitate was formed and stirred thoroughly for about 15 minutes, whereupon it was filtered by suction. The raw product thus obtained was washed with water until It contained only about Va% water-soluble salts. After drying for 12 hours In a vacuum apparatus at 60°C and under a pressure of 12 mm Hg, the product had the form of hard pieces. The pieces were comminuted to powder in a ball mill and the powder was passed through a sieve (3,600 meshes per cm ). The small residue on the sieve was again pulverized and passed through the same sieve. The yield was 870 g, or 99% of theoretical, calculated on the assumed formula... 

A simple calculation based on the solubility product of ferrous hydroxide and assuming an interfacial pH of 9 (due to the alkalisation of the cathodic surface by reaction ) shows that, according to the Nernst equation, at -0-85 V (vs. CU/CUSO4) the ferrous ion concentration then present is sufficient to permit deposition hydroxide ion. It appears that the ferrous hydroxide formed may be protective and that the practical protection potential ( —0-85 V), as opposed to the theoretical protection potential (E, = -0-93 V), is governed by the thermodynamics of precipitation and not those of dissolution. 

For AgCl and AgBr this quantity is negative (in agreement with a loss of entropy by solvent dipoles in the ionic fields). For Agl, on the other hand, it is zero. This implies, according to (168), that in this case AS0 happens to be equal to 2R In M in other words, the value happens to be 16.0 e.u. On referring to Sec. 90 it will, in fact, be seen that the value of AS0 calculated from the solubility of Agl at 25°C, and its heat of precipitation, was 16.0 e.u. 

With the aid of a table of solubility products of metallic sulphides, we can calculate whether certain sulphides will precipitate under any given conditions of acidity and also the concentration of the metallic ions remaining in solution. Precipitation of a metallic sulphide MS will occur when [M2 + ] x [S2 ] exceeds the solubility product, and the concentration of metallic ions remaining in the solution may be calculated from the equation ... 

It must be pointed out that the above calculation is approximate only, and may be regarded merely as an illustration of the principles involved in considering the precipitation of sulphides under various experimental conditions the solubility products of most metallic sulphides are not known with any great accuracy. It is by no means certain that the sulphide ion S 2 is the most important reactant in acidified solutions it may well be that in many cases the active precipitant is the hydrogensulphide ion HS , the concentration of which is considerable, and that intermediate products are formed. Also much co-precipitation and post-precipitation occur in sulphide precipitations unless the experimental conditions are rigorously controlled. 

Values for the solubility products of metallic hydroxides are, however, not very precise, so that it is not always possible to make exact theoretical calculations. The approximate pH values at which various hydroxides begin to precipitate from dilute solution are collected in Table 11.2. 

From the alpha-activity remaining in the supernatant liquid after the final precipitation as a fluoride, it can be calculated, using 30,000 years as the half-life of 94239, that this salt of 94 has a solubility of the order of magnitude of 10 mg of the element per liter of 6 N HF solution. This value is necessarily somewhat tentative. 

Self-Test 11.14A Potassium carbonate is added to a solution containing the following concentrations of soluble cations 0.030 mol-I 1 Mg2+(aq) and 0.0010 molT 1 Ca2+(aq). (a) Use the information in Table 11.4 to determine the order in which each ion precipitates as the concentration of K,CO, is increased and give the concentration of C032 when precipitation of each begins, (b) Calculate the concentration of the first ion to precipitate that remains in solution when the second ion precipitates. 

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