Rough hard spheres treatment of tracer diffusion of each component in two-component liquid systems

The rough hard spheres treatment of diffusion is extended to cover tracer diffusion of both species in five two-component organic liquid systems. Self-consistent results are obtained for the factor expressing coupling of translational-rotational motion and reasonable agreement is found where comparisons can be made with mutual diffusion data.     

Comparison of fluoro and chlorochromates (VI) as organic oxidants - a thermochemical approach

The standard enthalpies of formation of pyridinium and potassium fluoro- and chloro- chromates (VI) have been determined from their heats of alkaline hydrolysis. The unexpected ability of pyridinium fluorochromate to oxidise organic substances almost as well as the chlorochromate is rationalized in terms of the close enthalpy values for the oxidising couples CrO₃F^?/F^? and CrO₃Cl^?/Cl^?. The oxidising ability of fluoroselenates relative to the Group VI analogues, the fluorochromates, is also assessed.     

The characterization of the growth of sub-monolayer coverages (1/200th to 1 monolayer) of Si and Be on GaAs(001): A reflectance anisotropy spectroscopy and reflection high-energy electron diffraction study

The techniques of reflectance anisotropy spectroscopy (RAS) and reflection high-energy electron diffraction (RHEED) have been employed, for the first time in concert, to characterize the growth of sub-monolayer coverages of both Si and Be deposited onto the GaAs(001)-c(4×4) surface. The RHEED observations enabled the RAS spectra collected for a series of Si and Be coverages, in the range 0.005 to 1.000 monolayer (ML), to be interpreted in terms of changes in the sample surface structure. For the case of Si/GaAs(001) the following series of surface reconstructions were observed with increasing Si coverage: c(4×4), c(4×4)/(1×2), (1×2), (1×2)/(3×1) and, (3×1). During the deposition of Be/GaAs(001), c(4×4), c(4×4)/(1×2), c(4×4)/(1×3), (1×2)/(1×3), (1×3), and (1×2) reconstructions were noted to evolve. The fact that unique, but highly reproducible, RAS signatures were obtained for each of these surface phases demonstrates the applicability of a combined RHEED/RAS system for monitoring sub-monolayer heteroepitaxial growth with a surface sensitivity of the order of 1/200th of a monolayer.     

Inferences on dynamic water structure in aqueous solutions from diffusion measurements

The dynamic, hydrogen-bonded structure of water can be profoundly affected by addition of solutes as reflected by the resulting solute—solvent interactions. Measurements of diffusion coefficients for the solute species and for water are a useful probe for studying those interactions and changes in the dynamic water structure.

The analysis of transport properties of electrolyte solutions is presently approached both theoretically and experimentally by the use of generalised transport coefficients such as Onsager phenomenological coefficients, velocity correlation coefficients or the closely related distinct diffusion coefficients of Friedman. However, two of these approaches generally use a solvent-fixed frame of reference and thereby exclude the information available from studying the diffusion of the solvent.

The velocity correlation coefficient approach is used here to examine hydrogen-bonding effects in binary solution containing water as one component. We discuss also examples where intra-diffusion data for water in aqueous solutions give important insights into the dynamic structure of aqueous solutions.     

Intradiffusion coefficients of all species in aqueous gallium perchlorate solutions and solution viscosities at 25°C

Intradiffusion coefficients of all species (cation, anion and solvent) and viscosities have been measured for aqueous solutions of gallium perchlorate in the concentration range 0–2.3 mol-kg^–1 at 25°C. The perchlorate ion intradiffusion measurements were made using³⁶ClO ₄ ^– as the tracer species in diaphragm cell experiments. The development of a method to synthesize³⁶ClO ₄ ^– from³⁶Cl^– by electrolysis is described. The perchlorate intradiffusion coefficients results show a concentration dependence that is very similar to that for D(Cl^–) in corresponding trivalent metal chloride solutions. A simple hydration analysis based on all the transport results estimates a total (effective) cation hydration for gallium within a 0–2 mol-kg^–1 range of 10 (±1.5).     

The acidimetric estimation of fluoride. A comparison of the glass with the lanthanum fluoride electrode

A rapid potentiometric titration using cerium (III) chloride as titrant with a glass electrode indicator system is proposed for fluoride estimations. The alkali fluoride (0.002-0.02 M) initially adjusted to a pH of 6.3 ± 0.05 is titrated continuously. The equivalence point is measured directly from the recorder chart as the mean of two well defined points. Calibrations are carried out with fluoride solutions of about the same salt content, or by repeating the titration on another aliquot with a standard addition of fluoride. This procedure gives results as precise as those obtained previously with the fluoride electrode without elaborate computations. A direct comparison of glass and fluoride electrode systems with different titrants is provided.     

Determination of simple and complex iodides with ferric chloride-an alternative to the andrews titration

The iodide content of simple and complex iodides can be extracted as iodine after dissolution of the sample with acidified ferric chloride solution. Most iodides can thus be decomposed in 3M hydrochloric acid medium. A suitable extraction flask is described. Information on the cation oxidation state can be obtained by titrating the released ferrous ions in situ. A precision of 0.2% for 1-5 mmoles of iodide is attainable.     

Viscosity of aqueous NH4Cl and tracer diffusion coefficients of ions,water and non-electrolytes in aqueous NH4Cl,KI, and MgCl2 at 25°C

Viscosities for aqueous NH₄Cl and tracer diffusion coefficients for²²Na⁺,³⁶Cl^–, HTO, and CH₃OH, acetone and dimethylformamide (all¹⁴C-labelled) in NH₄Cl supporting electrolyte are reported for 25°, together with tracer diffusion coefficients for²²Na⁺,³⁶Cl^–, and¹⁴CH₃OH in 1M KI, and for¹⁴CH₃OH in 1M MgCl₂. The diffusion coefficient of HTO in NH₄Cl solutions is slightly larger, for most of the concentration range investigated (0.05 to 4.5 M), than the value for pure water and is almost unaffected by the supporting electrolyte up to about 4M. Similar behavior is shown by CH₃OH, acetone and dimethylformamide in NH₄Cl solutions. Onsager limiting law behavior is approached by Cl^– at NH₄Cl concentrations in the 0.05–0.1M region but at much lower concentrations by Na⁺.     

A redetermination of the heat of formation of perchloryl fluoride

A standard enthalpy of formation for perchloryl fluoride of ?22.6 ± 1.0 kJ mol^-1 was determined from its heat of alkaline hydrolysis which compared with a previously obtained value of ?26.5 ± 2.9 kJ mol^-1 from the heat of hydrogenation. A convenient calorimeter for gas-liquid reactions is described. The thermochemistry of hydrolysis and bond fission of perchloryl fluoride is discussed in relation to known reactions of the fluoride.