Calcium sulfate Dissociation constant

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. 

The coefficients in equations (26) and (27) for the dissociation of a number of acids and the solubility of calcium carbonate are given in Table A6.5 (Millero, 1979, 1995). The results for carbonic and boric acid are taken from the measurements of Culberson and Pytkowicz (1968). The effect of pressure on the solubility of calcite and aragonite has been determined from the measurements of Ingle (1975). The effect of pressure on the dissociation constants of water, hydrogen sulfate, hydrogen sulfide, ammonia, and hydroffuoric and phosphoric acids have been estimated from molal volume and compressibility data. 

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)... 

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)... 

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. 

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