Cerium selenites

Two determinations of the solubility product of cerium(lll) selenite are available. Little attention has been paid to the composition and quality of the solid phase, which will be denoted from lack of information as 002(8003)3(5) only. 

Chukhlantsev and Tomashevsky [57CHU/TOM] prepared cerium(lll) selenite by mixing 0.1 M solutions of selenious acid and a cerium(III) salt. The mixture was neutralised with ammonia at 333 K in order to precipitate cerium selenite. The separated selenite was dried at 313 K. No information on its quality is available but it is most likely amorphous. Chemical analysis showed a 2 3 ratio between Ce(III) and Se(IV). The solubility of the specimen in dilute solution of nitric or sulphuric acid was measured at 293 K. The experiments were performed and the data recalculated as outlined in Appendix A, [56CHU]. The result for  

8uponitskii, and Karapet yants [67MAI/8UP] made a calorimetric determination of the enthalpy change of the reaction between an aqueous solution of ce-rium(III) chloride and Na28e03(cr). The cerium selenite formed was amorphous. As no other datum exists for the enthalpy of formation of this compound the result of the investigation is included in the review but not selected. The calorimetric measurement is re-evaluated in Appendix A on the assumption that the selenite contains 10 molecules of water of crystallisation. The result is Af//° (Ce2(8eO3)3-10H2O, am, 298.15 K) = -(5732.8 +5.3) kJ-mol.  

The enthalpy of formation AH298 = -1367.6 kcal/mol is recommended by Schumm et al. [9]. 

The density is Df = 3.92 g/cm. The enthalpy of formation AH29s= -1208.7 0.5 kcal/mol is determined from the solution enthalpy 12.69 0.50 kcal/mol when 1.3 to 1.4 g salt are dissolved in 290 g HCl solution (1 5). For calculations of AH298 from the anhydrous salt, see the original paper [5]. 

The anhydrous compound forms on heating the pentahydrate in N2 at 110°C, see below, Giesbrecht, Giolito [6]. 

On heating 80 mg at a heating rate of 2.5 K/min at 540°C evolution of 8e02 and H2O is observed. The normal selenite is decomposed to Ce02 at 1060°C. A weight loss curve is given 

---

The authors reacted a solution of cerium(lll) or neodymium chloride with Na2Se03(cr) in an electrically calibrated calorimeter. The selenites precipitated were amorphous and contained 10 and 8 molecules of water, respectively, when dried at 298 K. These numbers have been used in the re-evaluation of the measurements. The recalculation used the values of the standard enthalpies of formation of Ce (aq) and Nd (aq) proposed in the critical evaluation by Cordfunke and Konings [2001COR/KON], see Appendix E, and of Cl (aq) in [89COX/WAG]. A correction for the enthalpy of dilution from (aq 1 1500) to the aqueous standard state of- (3.5 1.0) kJ-mol was applied. 

MA1/SUP] Maier, A. 1., Suponitskii, Y. L., Karapet yants, M. K., Heats of formation of cerium and neodynium selenites, Izv. Akad. Nauk SSSR, Neorg. Mater., 3, (1967), 1511-1513, in Russian, English translation in [67MA1/SUP2]. Cited on pages 374, 380, 494, 552, 553. 

Another possible application has emergfed recently. Cerium(IV) selenite, prepared previously by Markovskii and Safina (1968), shows promising ion exchange properties, especidly toward Hg(II) (Rawat et al., 1984 Husain et al., 1984). 

---