1.1 THE SIGNIFICANCE AND PHENOMENOLOGY OF IONS IN SOLUTION
Chemistry is for a large part conducted in solutions involving ions and such solutions are ubiquitous in nature. Oceans are vast aqueous solutions of salts, consisting mainly of sodium chloride, but other salts and minor components are also present in ocean water. Lakes, rivers, and brackish water are dilute solutions of ions and are essential to survival, since they provide drinking water and water for irrigation. Rain and other precipitates may remove ionic species from the atmosphere that arrived there as spray from oceans and seas or from human activities, for example, acid rain. Physiological fluids consist mostly of water in which colloidal substances, but also ions essential to their function, are dissolved.
It appears from the above that water is the only medium in which ions play a role, but this picture is too narrow because human endeavors utilize many other liquid media in which ions are present and have an active role. The manufacture of organic substances, as raw materials or intermediates in many industries, such as textiles, drugs, and food additives, generally involves reactions carried out in mixed aqueous-organic or completely nonaqueous liquid media in which ions participate. In chemical analysis, such media have long been of invaluable use, for instance in electroanalytical measurements or chromatographic separations. Industrial uses of nonaqueous media involving ions include solvent extraction in hydrometallurgy or in nuclear fuel reprocessing and nuclear waste disposal (Chapter 8).
The ions involved in these as well as other systems and applications interact with each other and with nonionized solutes that may be present. These interactions are of prime interest to the chemist, but the extent, intensity, and rate of proceeding of these interactions depend heavily on the solvent or solvent mixture present, a fact that is not always clearly recognized by the operator. The ion–solvent interactions should be understood in order to make the best use of the solutions of the ions, since it is the solvated ions that take part in the interactions of interest. If a free choice of the solvent or the solvent mixture to be used is possible, the most suitable one for the purpose should be selected on the basis of the knowledge available on the interactions that take place, bearing in mind also costs, ecology, and hazards. If the solvent is prescribed, this knowledge is still needed in order to select the proper reaction conditions or the additives that could be useful. So-called “bare” or nonsolvated ions occur in gas-phase reactions (Chapter 2) but not in condensed ...
