The heat of dissolution of uranyl nitrate in aqueous nitrate solutions

Conclusions A model has been suggested to explain the observed relationship between the measured heats of dissolution of uranyl nitrate in aqueous nitrate solutions and the concentration of the salting-out agent. The model describes the change in the structure of water in the solution with change in its concentration. On the one hand, a destruction of the water structure by ions occurs, which is weakened with increase in the distance from the ion, and leads to such irregularity in the distribution of water molecules in the solution that the mean number of molecules of water in unit volume is increased with increase in the distance from the ions. In experiments on the heat of dissolution this increase leads to increased hydration of the uranyl cation and reduction in the endothermicity of the dissolution with increase in the concentration of the solution. On the other hand, an interaction occurs between the ions of the salting-out agent and the water molecules in the solution, leading to the opposite result: There is an increase in the mean number of water molecules of the solution in unit volume in the direction of these ions. In experiments on the heat of dissolution this is revealed in the dehydration of the uranyl cation, and correspondingly in an increase in the endothermicity of the dissolution with increase in the concentration of the solution. The proposed model is in harmony with data on vapor pressure above the solutions (the relationship between the activity coefficient of the water and the concentration of the solution).Translated from Zhurnal Strukturnoi Khimii. Vol. 3, No. 2, pp. 143–150, March–April. 1962     

Determination of free acidity in uranyl nitrate solutions

Two modifications of the existing method of determining free acidity in highly concentrated uranyl nitrate solutions by alkalimetric titrations in neutral potassium oxalate medium have been carried out to improve the reliability of the method. Free acidities of several synthetic solutions containing uranium and nitric acid in a wide range of concentration ratios were determined by all the three methods and compared with the results obtained by a more accurate ion exchange method. Interference from other hydrolyzable ions and the precision and accuracy were studied and compared.     

Determination of small amounts of TBP and DBP in uranyl nitrate solutions

Tri- and dibutylphosphate (TBP and DBP) in concentrated uranyl nitrate solution are determined by a method based on the solvent extraction of zirconium-95. The distribution ratio of zirconium-95 between dilute solutions of TBP and DBP in dodecane and 10M hydrochloric acid and 1Mnitric acid respectively is measured. There is a logarithmic relationship between the distribution ratio and concentration of TBP and DBP, which enables them to be determined rapidly and with an error of +/- 10% over the range 1-100ppm of TBP and 40-600 ppm of DBP. The lower limit is 0.5 ppm for TBP and 10 ppm for DBP.     

Determination of organic peracids and hydrogen peroxide in mixtures

A simple method for the determination of organic peracids and hydrogen peroxide in mixtures is presented. The method is based on the instantaneous reaction of peracids with neutral potassium iodide and on the formation of a stable complex between hydrogen peroxide and titanyl ions. This complex is decomposed with sodium fluoride and the ensuing reaction with iodide is accelerated with molybdic acid. The influence of the different additives on the analytical results has been studied.     

Effect of temperature on hydrogen peroxide photolysis in aqueous solutions

The photolysis of hydrogen peroxide in dilute aqueous solution (1 × 10⁻⁴ M) at various temperatures (15–85°C) and pH (ph 2.5–7) was studied by flash photolysis. The rate of oxygen production under continuous photolysis conditions was measured at room temperature. The rate constants and activation parameters are reported. Evidence for the formation of complexes between hydrogen peroxide and intermediate radicals is presented. The liquid phase data are discussed and compared with those available for the gas phase.     

Decomposition of hydrogen peroxide in aqueous solutions at elevated temperatures

Decomposition of hydrogen peroxide in high-purity water has been measured at temperatures ranging 100 to 280°C in a laboratory test loop. A first-order decomposition kinetics has been observed in all cases, but the decomposition rates were found to vary widely, depending on the material used in the reaction chamber. In a 4 mm ID stainless steel tubing, the decomposition rate constant is determined to be k = 2 × 10⁵ exp(?14800/RT). This decomposition rate is approximately 100 times faster than that observed in a Teflon tubing. The variation of decomposition rate in different reaction chambers is attributed to the heterogeneous catalytic effects. There is no evidence of reaction between H₂ and H₂O₂ in the highpurity water at temperatures up to 280°C.     

Extraction of uranyl nitrate from aqueous nitrate solutions by open cell polyurethane foam sponge (OCPUFS)

The extraction of uranyl nitrate into open cell polyurethane foam sponge (OCPUFS) from aqueous solution, in the presence of salting agents, has been examined. The extraction efficiency was observed to depend on the concentration of uranyl and nitrate ions. The charge of the cation was also found to influence the distribution ratio. The effect of the change in temperature and pH was also studied. The results are interpreted in terms of OCPUFS acting as a viscous organic ether of moderate dielectric constant.     

Uptake of methacrolein into aqueous solutions of sulfuric acid and hydrogen peroxide

Multiphase acid-catalyzed oxidation by hydrogen peroxide has been suggested to be a potential route to secondary organic aerosol (SOA) formation from isoprene and its gas-phase oxidation products, but the kinetics and chemical mechanism remain largely uncertain. Here we report the first measurement of uptake of methacrolein into aqueous solutions of sulfuric acid and hydrogen peroxide in the temperature range of 253-293 K. The steady-state uptake coefficients were acquired and increased quickly with increasing sulfuric acid concentration and decreasing temperature. Propyne, acetone, and 2,3-dihydroxymethacrylic acid were suggested as the products. The chemical mechanism is proposed to be the oxidation of carbonyl group and C═C double bonds by peroxide hydrogen in acidic environment, which could explain the large content of polyhydroxyl compounds in atmospheric fine particles. These results indicate that multiphase acid-catalyzed oxidation of methacrolein by hydrogen peroxide can contribute to SOA mass in the atmosphere, especially in the upper troposphere.     

The determination of hydrogen peroxide in aqueous solutions by square wave voltammetry

Hydrogen peroxide in aqueous solutions can be determined directly by square wave voltammetry. The method is applicable to samples with a large range of pH in matrices ranging from distilled de-ionized water to sea-water. Its dynamic range extends from 0.5 to at least 1000 microM and the precision is about +/-6% at 2.5 microM and +/-2% at 215 microM. In comparison to DC and differential pulse polarography, by using square wave voltammetry the scan time is reduced from minutes to a fraction of a second, the sensitivity is increased by several-fold and the dynamic range has been greatly expanded at both the lower and the upper end by at least an order of magnitude. The low detection limit allows this method to be applied to the determination of H(2)O(2) in some samples of rainwater.     

Kinetics and mechanism of the reactions of uracil with hydrogen peroxide in aqueous solutions

The kinetics of the reactions of 5-hydroxy-6-methyluracil and 6-methyluracil with hydrogen peroxide in aqueous solutions has been investigated. The reactions proceed via two competitive mechanisms, namely, free-radical and nonradical ones. The iron ions present in water as impurities make possible the free-radical mechanism.     

Potentiometric determination of free acidity and uranium in uranyl nitrate solutions

Free acid and uranium in uranyl nitrate solutions have been determined potentiometrically using Na₂SO₄–NaOH, Na₂SO₄–Na₂CO₃ and (NH₄)₂SO₄–NaOH complexant-titrant combinations. The overall recovery of nitric acid varies in the range of 95.25 to 118.5%, depending upon the acid as well as the total uranium present, while that of uranium always a positive bias ranging from 100.2 to 106.4%. The results have been discussed in light of recent available data. It has been concluded that all the complexant-titrant combinations studied provide similar results.     

Photoinduced formation of hydrogen peroxide in aqueous solutions of adenine derivatives at 77 K

The amount of hydrogen peroxide in aqueous solutions of adenine (A), adenosine (Ado), cytidine (Cyt), and thymine (T) containing 0.1 M NaCl and irradiated with near-UV light at 77 K is determined. It is established by comparing the results to data obtained earlier that the amount of H₂O₂ detected in the defrosted samples following identical irradiation falls in the order Ado > adenosine-5′-diphosphate (ADP) > A >> Cyt. The formation of H₂O₂ was not detected for T. The formation of H₂O₂ in solutions of adenine derivatives was observed when the samples were irradiated with light having wavelengths in the ranges λ = 240–400 nm and 290–450 nm. The latter covers only the long wave absorption range of these compounds. It is shown that the change in the intensity of irradiation that strongly affected the intensity оf EPR signals of irradiated samples prior to defrosting affected the amount of detected H₂O₂ only slightly, and the effect was not unidirectional. The results from determining H₂O₂ in the samples of adenine derivatives are compared to estimates of the content of free peroxyl radicals, obtained by analyzing EPR spectra. Plausible mechanisms of the processes are discussed.