Cerium oxalate

Cerium(IV) oxide may be obtained by heating cerium oxalate, carbonate or other salts at elevated temperatures ... 

Prepare cerium oxalate and see how it reacts with acids. What is the value of the solubility product of cerium oxalate ... 

Carbon (lampblack) P. 13 Carbon dioxide (cylinder or generator) P. 15, 71 Carbon tetrachloride E. 5 Cerium dioxide P. 50, 51 Cerium oxalate P. 49 Chlorine (cylinder or generator) P. 36,... 

The cerium hydroxyl carbonate could be obtained through hydrothermal treatments, for example the hydrothermal treatment of cerium oxalate (Li et al., 1996). The most feasible way is to utilize the sealed reaction of Ce with urea CO(NH2)2 in aqueous solution. The hydrolysis of urea in water leads to (NH4)2C03 and provides the base to change the... 

Cerium-oxalate, -carbonate and -hydroxide are considered to be the most important precursors for cerium-derivatives on a commercial scale. The cerium derivatives are yielded from these compounds by additional chemical and/or physical treatment. For example, cerium oxide may be formed easily by calcining cerium carbonate or/and cerium oxalate respectively. 

Derivation By decomposition of cerium oxalate by heat. Hardness depends on firing temperature. 

The resultant cerium nitrate solution, which is about 2N in HNO3, is filtered and slowly added in drops to a hot, concentrated solution of oxalic acid. The finely crystalline precipitate of cerium oxalate is suction-filtered, washed with a large quantity of water, dried and calcined to the oxide. 

Ubaldini and coworkers [79] studied the thermal decomposition of the mixed oxalates (Cei xGdx)2(C204)3-nH20. The mechanisms of decomposition of Ce and Gd oxalate are different, and mixed oxalates behave in an intermediate way. Their dehydration stages are more similar to those of Gd oxalate, because not all the molecules of water are equivalent, as they are in the cerium oxalate. The decomposition leads to (Cei xGdx)02-x/2- For x close to 0 or to 1, two solid... 

Ano er line of research that is arousing great interest in this area of research is the incorporation of corrosion inhibitors capable of playing an active role in protecting against corrosion similar to that of Cr +. Thus, studies are to be found that incorporate a wide variety of compounds such as cerium acetate, cerium oxalate, calcium borate, potassium metavanadate and cerium vanadate. 

Garboxylates. Cerium carboxylates, water-insoluble, can be made (11) by double decomposition and precipitation using water-soluble precursors, or by reaction of an insoluble precursor directly with the organic acid. Cerous oxalate [139-42-4] 2-ethyIhexanoate (octanoate),... 

However, solubility, depending as it does on the rather small difference between solvation energy and lattice energy (both large quantities which themselves increase as cation size decreases) and on entropy effects, cannot be simply related to cation radius. No consistent trends are apparent in aqueous, or for that matter nonaqueous, solutions but an empirical distinction can often be made between the lighter cerium lanthanides and the heavier yttrium lanthanides. Thus oxalates, double sulfates and double nitrates of the former are rather less soluble and basic nitrates more soluble than those of the latter. The differences are by no means sharp, but classical separation procedures depended on them. 

Method B Standardisation with sodium oxalate. Standardisation may also be carried out with sodium oxalate in this case, an indirect procedure must be used as the redox indicators are themselves oxidised at the elevated temperatures which are necessary. The procedure, therefore, is to add an excess of the cerium(IV) solution, and then, after cooling, the excess is determined by... 

Weigh out accurately about 0.2 g sodium oxalate into a 250 mL conical flask and add 25-30 mL 1M sulphuric add. Heat the solution to about 60 °C and then add about 30 mL of the cerium(IV) solution to be standardised dropwise, adding the solution as rapidly as possible consistent with drop formation. Re-heat the solution to 60 °C, and then add a further 10 mL of the cerium(IV) solution. Allow to stand for three minutes, then cool and back-titrate the excess cerium(IV) with the iron(II) solution using ferroin as indicator. 

Redox titrants (mainly in acetic acid) are bromine, iodine monochloride, chlorine dioxide, iodine (for Karl Fischer reagent based on a methanolic solution of iodine and S02 with pyridine, and the alternatives, methyl-Cellosolve instead of methanol, or sodium acetate instead of pyridine (see pp. 204-205), and other oxidants, mostly compounds of metals of high valency such as potassium permanganate, chromic acid, lead(IV) or mercury(II) acetate or cerium(IV) salts reductants include sodium dithionate, pyrocatechol and oxalic acid, and compounds of metals at low valency such as iron(II) perchlorate, tin(II) chloride, vanadyl acetate, arsenic(IV) or titanium(III) chloride and chromium(II) chloride. 

Experimental work was carried out on black sand in which the effect of sodium oxalate on monazite activation was examined. It should be noted that monazite is essentially a phosphate of cerium and lanthanum, where the possibility exists that sodium oxalate has an activating effect on monazite [11]. The use of sodium oleate as activator was studied with different sulphonate collectors (Table 24.12). 

The oxalates obtained above, alternatively, are digested with sodium hydroxide converting the rare earth metals to hydroxides. Cerium forms a tetravalent hydroxide, Ce(OH)4, which is insoluble in dilute nitric acid. When dilute nitric acid is added to this rare earth hydroxide mixture, cerium(lV) hydroxide forms an insoluble basic nitrate, which is filtered out from the solution. Cerium also may be removed by several other procedures. One such method involves calcining rare earth hydroxides at 500°C in air. Cerium converts to tetravalent oxide, Ce02, while other lanthanides are oxidized to triva-lent oxides. The oxides are dissolved in moderately concentrated nitric acid. Ceric nitrate so formed and any remaining thorium nitrate present is now removed from the nitrate solution hy contact with tributyl pbospbate in a countercurrent. 

In one acid digestion process, monazite sand is heated with 93% sulfuric acid at 210°C. The solution is diluted with water and filtered. Filtrate containing thorium and rare earths is treated with ammonia and pH is adjusted to 1.0. Thorium is precipitated as sulfate and phosphate along with a small fraction of rare earths. The precipitate is washed and dissolved in nitric acid. The solution is treated with sodium oxalate. Thorium and rare earths are precipitated from this nitric acid solution as oxalates. The oxalates are filtered, washed, and calcined to form oxides. The oxides are redissolved in nitric acid and the acid solution is extracted with aqueous tributyl phosphate. Thorium and cerium (IV) separate into the organic phase from which cerium (IV) is reduced to metalhc cerium and removed by filtration. Thorium then is recovered from solution. 

After separation from other rare earths, ytterbium is usually obtained as its oxide, Yb203. If separated as oxalate, oxalate is converted into oxide by high temperature. Ytterbium oxide is reduced to metallic ytterbium by heating with lanthanum metal in high vacuum. The metal is purified by sublimation and collected over a condenser plate. Aluminum, zirconium, and cerium also are effective reducing agents and may be used instead of lanthanum. 

Two polarographic methods have been developed for the determination of cohalt(II) at concentrations ranging from approximately 1 to 80 mM in an aqueous sample. For the first method [15], which is suitable for samples containing large amounts of nickel]11), the cobalt(II) is oxidized to Co(NH3)6 in an ammoniacal medium with the aid of sodium perborate, after which the cobalt(III) species is determined. A second procedure [16] entails the use of lead dioxide in an acetic acid-acetate buffer containing oxalate to convert cobalt(II) to the 0(0204)3 ion, which can be subjected to polarographic reduction. This latter approach is well suited to the determination of cobalt in the presence of copper(II), iron(III), nickel(II), tin(IV), and zinc(II), whereas the chief interferences are cerium, chromium, manganese, and vanadium. 

Secondly, we studied the oxidation of oxalate by cerium(IV) in sulfuric acid. This reaction is analagous to the classical manganese (111) oxalate reaction studied by H. Taube and also by F. Duke. Indeed, it proceeds through an intermediate containing one or more oxalates per cerium. This decomposes to give cerium(III) and other products. The point I want to raise is that we have been able to detect free radicals in this reaction, using EPR experiments and a flow system. So far, it has not been possible to say whether the radical is the oxalate or CO2 radical, both of which have been proposed in other studies. 

K bicarbonate, K chloride, K iodide, K metaphosphate, K perchlorate, K phosphate, K silico-fluoride, K urea oxalate, sodium ammonium sulfate, sulfur, zinc sulfate and Zr oxide It was claimed that methylene urea reduced the flash to a far greater extent than any of the organic compounds used, ft was also stated that cerium salts were much more effective than any other metallic salts investigated (Ref 4)... 

An analogous reaction, but one in which one ligand supplies two electrons, has been observed for the oxidation of pentammineoxalatocobalt(III) by cerium-(IV). Saffir and Taube (10) have shown the oxalate is oxidized to carbon dioxide in a two-electron transfer, producing one equivalent of cobalt (II) and one equivalent of cerium (III). 

It was established that unreacted oxalato complex, Cr(OH2) +3, and free oxalate do not interfere in the titration. Thus the concentrations of cerium(IV) could be readily measured as a function of time. 

It is apparent that Cr(C2C>4)3 3, m-Cr(OH2)2(0204)2 , and Cr(0H2)4C2044 react smoothly with cerium(IV) in acidic-sulfate media, 1 mole of oxalate being oxidized for each 2 moles of cerium(IV) consumed. The observations made are consistent with the view that the three reactions proceed, at least initially, according to the stoichiometries represented by the respective Reactions 3,1, and 2. The initial absorbances of reactant solutions (values obtained by extrapolation of measured absorbances to zero time) agree well with the values calculated, on the basis of Beer s law, from the absorptivity coefficients of the components. Further, as the reactions in 1.83Af sulfuric acid proceed, the absorbances of the solutions move toward the values expected for the assumed products at rates which demonstrate the reactions are first order in cerium(IV) and complex—see, for example, Figure 2. We thus find no indication that reaction intermediates contribute measurably to the absorbances of reactant solutions, or that reaction conditions cause the rapid equilibration of any of the oxalato complexes with other species... 

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