Calcium sulfate constant

C16-0105. Write the equilibrium reaction and equilibrium constant expression for each of the following processes (a) Trimethylamine, (CH3)3 N, a weak base, is added to water, (b) Hydrofluoric acid, HF, a weak acid, is added to water, (c) Solid calcium sulfate, CaSOq, a sparingly soluble salt, is added to water. 

As examples of some water-soluble salts, mention may be made of potassium chloride, copper sulfate, and sodium vanadate. As examples of some water-insoluble salts, mention may be made of some typical ones such as lead chloride, silver chloride, lead sulfate, and calcium sulfate. The solubilities of most salts increases with increasing temperature. Some salts possess solubilities that vary very little with temperature or even decline. An interesting example is provided by ferrous sulfate, the water solubility of which increases as temperature is raised from room temperature, remains fairly constant between 57 and 67 °C, and decreases at higher temperatures to below 12 g l-1 at 120 °C. Table 5.2 presents the different types of dissolution reactions in aqueous solutions, and Table 5.3 in an indicative way presents the wide and varied types of raw materials that different leaching systems treat. It will be relevant to have a look at Table 5.4 which captures some of the essential and desirable features for a successful leaching system. 

A violent explosion followed the use of magnesium perchlorate to dry wet fluo-robutane. The latter was presumed to have hydrolysed to give hydrogen fluoride which had liberated perchloric acid, explosively unstable when anhydrous. (This explanation seems unlikely in view of the large disparity between dissociation constants of the two acids). Magnesium perchlorate is unsuitable for drying acidic or flammable materials calcium sulfate would be suitable. 

Values from Refs. (272,646) are derived from measurements of the solubility of calcium sulfate in solutions of the respective sugars (at 298K, 0.2stability constants from solubility measurements has been reviewed - see Ref. (225). 

After the addition was completed, the ethanol was removed under reduced pressure, and the residue was suspended in approximately 100 ml. of ether, filtered, and washed several times with ether. The yield was 25 g. (83.8%), and the salt was dried to a constant weight in a vacuum desiccator containing calcium sulfate (2 days). 

Alternatively, antisealants can be used to control calcium carbonate scale at LSI values as high as 2.0-2.5, depending on the specific antisealants. Calcium also forms scales with fluoride, sulfate, and phosphate. The LSI will not help predict these scales analysis of water quality, using the ion product and solubility constants, is required to determine the potential for scaling with calcium fluoride or calcium phosphate. Antisealants currently available can address calcium fluoride and calcium sulfate scale they do not address calcium phosphate scale (although newer antisealants will be available in the near future to address this scale). 

Barium and strontium form sulfate scales that are not readily soluble. In fact, barium is the least soluble of all the alkaline-earth sulfates. It can act as a catalyst for strontium and calcium sulfates scale.4 Analyses of the ion product with the solubility constants for barium and strontium sulfates is necessary to determine the potential for scaling with these species. If the ion product (IP) for barium sulfate exceeds the solubility constant, scale will form. Note that in the case of strontium sulfate, if IP > 0.8Ksp, scaling is likely. However, the induction period (the time it takes for scale to form) is longer for these sulfate-based scales than it is for calcium carbonate scale. 

Calcium sulfate is a sparingly-soluble salt. As with barium and strontium sulfate, the potential to scale with calcium sulfate is high when the ion product exceeds 80% of the solubility constant. Antisealants or sodium... 

Place in an eight-inch tube 5 ml of the unsaturated hydrocarbon and 5 ml of cold 70 per cent sulfuric acid. Cool the mixture in tap water, place a solid rubber stopper in the mouth of the tube, and shake with cooling until the hydrocarbon dissolves and a clear liquid results. Add 6 g of ammonium sulfate dissolved in 8 ml of water. Insert the separatory stopper, and remove the aqueous acid layer. The liquid which is left in the reaction tube can be tested with bromine water or alkaline permanganate to show that it is not an olefin. If it is desired to purify the alcohol, add 1 g of anhydrous calcium sulfate and shake from time to time over a period of fifteen minutes. Pour the crude alcohol into a distilling tube. Heat with a small flame and collect the proper fraction. If amylene is used, and the water is not completely removed by the drying agent, a constant boiling mixture will be formed which boils at 87°. 

Calcium sulfite and calcium sulfate scaling in the system can be a problem for the lime/limestone wet scrubber systems. Scaling occurs when the solutions are supersaturated to a point where heterogeneous crystallization (crystallization on foreign surfaces such as the scrubber walls, overfiow pots, marbles) takes place, resulting from nucleation. The ratios of the products of the activities (A) of Ca and S04 " or to their solubility product constants Kgp) as a measure of the degree of supersaturation are ... 

Laboratory experiments have shown that heterogeneous crystallization is not significant until the ratio of the activity product to the solubility product constant reaches about 1.5 for calcium sulfate and about 7 for calcium sulfite. 

Water can be determined in solid samples by infrared spectroscopy. The water content of calcium sulfate hydrates is to be measured using calcium carbonate as an internal standard to compensate for some systematic errors in the procedure. A series of standard solutions containing calcium sulfate dihydrate and a constant known amount of the internal standard are prepared. The solution of unknown water content is also prepared with the same amount of internal standard. The absorbance of the dihydrate is measured at one wavelength ( sample) along with that of the internal standard at another wavelength (As,d). The following results were obtained. 

Anhydrous zirconium phosphate (P04/Zr = 2) and the dihydrate are prepared by adding 100 ml of 1 ilf zirconium oxychloride 8H20 dropwise to constantly stirred, refluxing phosphoric acid solution prepared by dissolving two moles of sodium dihydrogenphosphate H2O in 200 ml of 3 ilf HCl. The zirconium phosphate gel is refluxed in its mother liquor for 25 hours and then washed until free of chloride. When air-dried, the dihydrate or y phase was obtained when vacuum-dried over calcium sulfate, the anhydrous a phase was obtained 117). 

This is perhaps the most common type of chemical interference. The presence of certain anions may cause refractory compounds to be formed with the analyte. As a consequence, its atomisation is hindered and a decrease in response is observed. A weU-known example is the suppression of the response of Ca with increasing concentrations of phosphate or sulfate. When the anion concentration in the flame is increased while keeping the calcium concentration constant, the absorbance decreases to about half its original value which is attributed to the formation of hardly dissociated calcium phosphate or sulfate. At high anion concentrations, the analyte response again becomes independent of the anion concentration. 

Equations E23.2.8 and E23.2.9 can be solved using the appropriate initial and boundary conditions to compute the concentrations of A in the continuous and microphases as functions of time. However, these model equations depend on the average particle diameter, surface area, and volume of the microphase. Because they are constantly changing as more crystals nucleate and grow, complete knowledge of the crystallization kinetics of calcium sulfate is necessary to solve the equations. 

Ainsworth, R.O., "Dissociation constant of calcium sulfate from 25 to SO°C", J. Chem. Soc. Faraday Trans I, v69, ppl028-1032 (1973)... 

G39. Marshall, W.L. E.V. Jones, "Second dissociation constant of sulfuric acid from 25 to 350" evaluated from solubilities of calcium sulfate in sulfuric acid solutions", J. Phys. Chem.. v70. 12, pp4028-4040 (1966)... 

G42. Marshall, W.L., R. Slusher. "The ionization constant of nitric acid at high temperatures from solubilities of calcium sulfate in HNO3-H2O, 100-350"C activity coefficients and thermodynamic functions , J. inorg. nucl. Chem., v37, PPH91-1202 (1975)... 

G44. Martynova, O.i. L.G. Vasina, S.A. Pozdnyakova, V.A. Kishnevskii, "Use of the calcium-selective electrode for determining the solubility product and dissociation constant of calcium sulfate", Doklady Akad. Nauk SSSR, v217, 4, PP862-864 (1974)... 

G72. Yeatts, L.B. W.L. Marshall, "Apparent invariance of activity coefficients of calcium sulfate at constant ionic strength and temperature in the system CaSOH-NazSOH-NaNOs-HaO to the critical temperature of water. Association equilibria", J. Phys. Chem., v73, 1, pp81-90 (1969)... 

Calcium sulfate precipitates from water as gypsum, the dihydrate, CaS04 2H20. If water can be taken to be at unit activity, or at least as constant, the mathematical form of our treatment is not changed. 

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