Strontium selenates

The enthalpy change of Reaction (V.181) was studied in [59SEL/ZUB3]. Two values were evaluated in Appendix A from the data, namely A //° ((V.181), 298.15 K)= (0.98 + 0.17) kJ moP from the temperature variation of the solubility 

The value in [82WAG/EVA] is - 1142.7 kJ-moP. Most of the difference, 9.5 kJ-moP, is probably caused by the selection of new auxiliary data. 

The standard Gibbs energy of formation of strontium selenate is obtained from the Gibbs energy of Reaction ((V.181)) and the selected values of AfG° for the ions to be AfG°(SrSe04, cr, 298.15 K) =-(1028.20 1.90) kJ-mol.  

The value of the standard entropy is smaller than expected from a comparison with data for alkaline earth sulphates in [82WAG/EVA] and indicates a systematic error in the formation data, which could not be traced from the experimental data available. No formation values for strontium selenate have therefore been selected. 

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The solubility of SrSe04(cr) in water has been determined over the temperature interval 273 to 373 K. Crystalline strontium selenate was prepared by mixing stoichiometric amounts of strontium nitrate and selenic acid. Under the light microscope the crystals appear as very thin needles. The strontium concentration in saturated solution was obtained by polarographic (half-wave potential at -2.1 V) and gravimetric measurements. Both methods gave concordant results, Table A-18. 

Table A-19 Solubility of strontium selenate in water in the temperature interval 273 to 373 K. Equilibration times 3 to 33 days.

SEL/ZUB] Selivanova, N. M., Zubova, G. A., Physico-chemical properties of strontium selenate, hv. Vyssh. Uchebn. Zaved, Khim. Khim. Tekhnol, 1, (1958), 27-33, in Russian. Cited on pages 405,456. 

The normal sulphates usually form well-defined crystals containing water of crystallisation, and frequently exhibit isomorphism not only with one another2 but in some cases also with the corresponding selenates, telluxates and chromates. They are generally fairly soluble in water, the chief exceptions being the sulphates of barium,3 strontium and lead, which are commonly classed as insoluble, and of calcium and silver, which are sparingly soluble.4,... 

With the exception of the calcium, strontium, barium and mercurous salts, the normal selenates are readily soluble in water. Barium chloride and mercurous nitrate are therefore convenient precipitation agents.6 Barium selenate is, however, more soluble than barium sulphate, and also differs from the latter salt in being slowly reduced to selenite by hydrochloric acid 7 for these reasons precipitation with barium chloride is not applicable to the quantitative determination of selenie acid. A concentrated solution of selenie acid which has been saturated with barium selenate deposits crystals of barium selenie acid, H2[Ba(Se04)2].8... 

Se03Sr Strontium selenite, 3 20 Se04H2 Selenic acid, 3 137 Se(S2CN(CH3)2)2 Selenium(II) di-methyldithiocarbamate, 4 93 Se(S2CN(C2H6)2)2 Selenium(II) di-ethyldithiocarbamate, 4 93 Se(S2COCH3)2 Selenium(II) meth-ylxanthate, 4 93... 

EXPLOSION and FIRE CONCERNS combustible solid NFPA rating (NA) reacts to form explosive products with metal amides contact with acids may cause formation of poisonous hydrogen selenide gas incompatible or reacts violently with barium carbide, bromine pen-tafluoride, chromic oxide, fluorine, lithium carbide, lithium silicon, metals, nickel, sodium, nitric acid, nitrogen trichloride, oxygen, potassium, potassium bromate, rubidium carbide, zinc, silver bromate, uranium, strontium carbide, and thorium carbide toxic gases and vapors may be released in a fire involving selenium, sodium selenite, sodium selenate, and selenium dioxide use water for firefighting purposes. 

SeOiSr Strontium selenite, 3 20 SeOiHs Selenic acid, 3 137 SeSr Strontium selenide, 8 11, 20, 22... 

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