Lanthanum selenates

The measurements of Serebrennikov and Tsybukova [79SER/TSY] indicate that La2(Se04)3 5H20 is the stable lanthanum selenate in contact with water at 298.15 K. The reported solubility at this temperature is accepted  

Smolyakova, Efremov, and Serebrennikov [73SMO/EFR] determined the enthalpy change of the reaction between La2(Se04)3-5H20(cr) and a solution of barium chloride with formation of BaSe04(cr) by a calorimetric measurement. The review calculated  

No other thermodynamic data have been found for lanthanum selenates. 

The compound is prepared from Y(OH)3 and dilute aqueous solutions of H28e04 by slow evaporation at 45°C until crystallization. After recrystallization and evaporation in vacuum at room temperature, the crystals were dried on filter paper. 2(8604)3-8 H2O is monoclinic, space group probably A2/a-C h (No. 15) interplanar spacings and relative intensities of the powder diagram are given. The lattice parameters are a = 18.58 0.02, b = 6.78 0.01, c = 13.65 0.02 A p = 102° 20 V = 1704A3 Z = 4. Dexp = 2.90, Dcaic = 2.92 g/cm, Perret et al. [1]- 

The product is mentioned by Nabar, Paralkar [2]. It is prepared from 2(003)3 dissolved in a little excess of H28e04. The clear solution was concentrated on a water bath and later allowed to crystallize slowly over P2O5 in a desiccator protected from light. The water content was estimated by thermogravimetric analysis. For the IR and Raman spectra, see p. 457, Gupta et al. [3]. 

The compound forms on heating the hydrated selenates. For example, La2(8e04)3-5H20 (stable up to 90°C) is dehydrated completely at 410°C, as shown by thermogravimetric investigations of Nabar, Paralkar [1] an endothermic effect in the DTA curve is observed at 180°C, see p. 469. Earlier, Friend [2] obtained La2(8e04)3 by heating the pentahydrate at 180°C for 8 h and then at 200°C for 4 h. 

In aqueous La2(8e04)3 solutions at 0 to 43°C, the composition of the solid residues approximates that calculated for the 22-hydrate. Several of the salts are distinctly basic. The salt obtained at 35°C with 7.8% H2Se04 added was acidic. At 43°C, La2(Se04)3-12H20 is obtained. Owing to hydrolysis, the saturated solutions are usually slightly acid. A true 

When 2.08 or 7.80% H2Se04 is added to the solution at 35°C the solubility is reduced from 31.2 (calculated) to 28.96 and 24.07 wt%. At83.6°C, the solubility is increased from 3.25 (calculated) to 4.81 wt% by 1.68% H2Se04, Friend [2]. The electrical conductivity of a 1.25 x 10 M solution indicates the existence of five ions in the solution, Gomez Madrazo et al. [3]. 

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Lanthanum selenate dodecahydrate can be crystallized from aqueous solutions near 0°C but the crystals are unstable towards dehydration (Karvinen and Niinisto, 1986). A structural analysis shows that half of the water molecules are not coordinated to lanthanum but are held between the layers by hydrogen bonds. There are five selenate and three water oxygens around lanthanum at normal... 

Bina Selenides. Most biaary selenides are formed by beating selenium ia the presence of the element, reduction of selenites or selenates with carbon or hydrogen, and double decomposition of heavy-metal salts ia aqueous solution or suspension with a soluble selenide salt, eg, Na2Se or (NH 2S [66455-76-3]. Atmospheric oxygen oxidizes the selenides more rapidly than the corresponding sulfides and more slowly than the teUurides. Selenides of the alkah, alkaline-earth metals, and lanthanum elements are water soluble and readily hydrolyzed. Heavy-metal selenides are iasoluble ia water. Polyselenides form when selenium reacts with alkah metals dissolved ia hquid ammonia. Metal (M) hydrogen selenides of the M HSe type are known. Some heavy-metal selenides show important and useful electric, photoelectric, photo-optical, and semiconductor properties. Ferroselenium and nickel selenide are made by sintering a mixture of selenium and metal powder. 

Iron(II) fluoride Iron(II) hydroxide Iron(III) hydroxide Iron(III) phosphate dihydrate Lanthanum iodate Lead(II) bromide Lead(II) carbonate Lead(II) chloride Lead(II) fluoride Lead(II) hydroxide Lead(II) iodate Lead(II) iodide Lead(II) selenate Lead(II) sulfate Lithium carbonate Lithium fluoride Lithium phosphate Magnesium carbonate Magnesium carbonate trihydrate... 

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