Interatomic structure of aqueous ionic solutions
| Autor: | G. W. Neilson |
|---|---|
| Rok vydání: | 1993 |
| Předmět: | |
| Zdroj: | Pure and Applied Chemistry. 65:2583-2587 |
| ISSN: | 1365-3075 0033-4545 |
| DOI: | 10.1351/pac199365122583 |
| Popis: | A knowledge of the structural properties of aqueous solution helps provide valuable insight into the rich variety of chemical and physical behaviour which such systems exhibit. Besides helping to characterise the interatomic coordination, such information can also be used to test the validity of theoretical model calculations. INTRODUCTION AND BACKGROUND In a paper delivered at the 19th Conference in this series on Solution Chemistry (ll, it was demonstrated how X-ray and neutron diffraction methods could be used to determine the pairwise structure of aqueous electrolyte solutions. In particular, it was shown that for an aqueous electrolyte solution of the form of a salt MXn in water (H20) these methods give information ont the ten pair radial distribution functions g,b(r). These ten g,p(r)'s can be conveniently grouped into three sets which refer to (i) the structure of the solvent - gHH(r), goH(r) and goo(r), (ii) the structure of the solute - gMM(r), gMx(r) and gxx(r), and (iii) the solute-solvent structure - gMo(r), gVH(r), gX&) and gXH(r). The difference methods of neutron diffraction and isotopic substitution (NDIS), and X-ray diffraction and isomorphic substitution (XDIS) enables one to probe these three aspects of a solution with varying degrees of quantitative accuracy. It will be recalled that prior to our previous article (ll which was published in in 1988, our primary interest was in the characterisation of the aqua ion structure as defined by GI(r) which to a good approximation is given by a linear sum of gIo(r) and gIH(r). (NDTS difference methods were initially applied to salts dissolved in heavy water (D20); this served to minimise systematic and statistical errors which arise when water (H20) is employed. Because of improvements in instrument design and computer codes, and an increase in neutron fluxes the NDIS methods can be used nowadays on samples which contain H20.) A systematic study was made and information obtained from the first order difference NDIS method for about twelve aqua ion species. It was also shown that results from NDIS experiments performed at the second order difference level could be used to determine ion-ion correlations in particularly favourable systems. This work was augmented by XDIS studies on a few specific systems which were susceptible to the isomorphic difference method. The combined picture which emerged was that both X-ray and neutron diffraction could be used to provide quantitative information of interionic structure in aqueous solutions. Application of NDIS methods was limited only by neutron fluxes and samples characterisation and successful work had been carried out on two systems. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|