Uranyl oxalate, decomposition

Uranyl oxalate actinometer. This actinometer has a range of 208-435 nm with an average quantum yield of about 0.5. Since the UO + ion acts as a photosensitizer for the oxalate decomposition the light absorption remains constant, but rather long exposures. re required for final accurate oxalate titrations. It is now mainly of histo al interest. 

Example of Application Large-Scale Actinometry. Neural network modelling was applied to large-scale actinometry in a continuous elliptical photochemical reactor with a concentric annular reaction chamber [2, 3,108, 148], Uranyl oxalate was used as an actinometer, which is based on the photosensitized decomposition of oxalate ions (Eq. 89) [2, 3] the experimental data were taken from the literature [108],... 

Example The quantum efficiency after the decomposition of uranyl oxalate in an experiment was found to be 0.570 at 300 nm. When light was passed through an empty cell, decomposition of 6.201 10-3 mole of the oxalate took place in 2 hours. When the cell contained acetone and irradiation continued for 10 hours, 1.4 10-3 mole of acetone were decomposed and light not absorbed by acetone decomposed 2.631 10-2 mole of the oxalate. What is the Quantum efficiency for the acetone decomposition ... 

The quantum yield for oxalate decomposition is relatively independent of pH for acidic solutions, in addition to being independent of temperature, concentration of reactants, and light intensity. The absorption of light by the uranyl oxalate system results in the generation of LMCT excited states. Such an absorption results in the formation of carbon dioxide and the reduced UC ion ... 

In an inert atmosphere, the decomposition at 573—623 K of uranyl(VI) oxalate [1101] obeys the Prout—Tompkins equation [eqn. (9)] with E = 261 4 kJ mole-1. The residual product is U02 and, under low pressure accumulatory conditions, the final CO2/CO ratio is 9. In air, the reaction proceeds in two stages. The initial process obeys the Prout—Tompkins equation and is identified as a surface reaction. Thereafter, decomposition fits the Avrami—Erofe ev equation [eqn. (6), n = 2], involving isolated disc-like grains of reactant, to yield amorphous U03 as the final product. Values of E for both stages of reaction are close to that found for reaction in the inert atmosphere ( 260 kJ mole-1) and comparable with theoretical predictions [88],... 

Example Radiation of wavelength 250 nm was passed through a cell containing 10 ml of a solution which was 0.05 molar in oxalic acid and 0.01 molar in uranyle sulphate. After absorption of 80 joules of radiation energy, the concentration of oxalic acid was reduced to 0.04 molar. Calculate the quantum yield for the photochemical decomposition of oxalic acid at the given wavelength. 

The quantum efficiency is usually determined by using a chemical reaction of known efficiency (actinometer) as a standard. The most commonly used reaction is the uranyl-ion-catalyzed decomposition of oxalic acid into water, carbon dioxide, and carbon monoxide, which has a quantum efficiency of 0.55 and is essentially independent of wavelength between 200 and 400 m. The apparatus consists of a solution of uranyl sulfate (0.01 M) and oxalic acid (0.05 M) maintained at 25° and contained in a cell of sufficient thickness to permit adsorption... 

The decomposition of oxalic acid photosensitized by uranyl ion is a common actino-metric reaction. The light may have any wavelength between 250 and 450 nm. The absorption of the light quantum activates the uranyl ion, which transfers its energy to a molecule of oxalic acid, which then decomposes. The reaction may be written... 

An accompanying reaction that does involve reduction of the uranyl ion to 1)021 makes only a minor contribution to the total decomposition of oxalate... 

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