Aqueous solutions overview

In view of the difficulties that accompany the use of a nonaqueous solvent, one may certainly ask why such use is necessary. The answer includes several of the important principles of nonaqueous solvent chemistry that will be elaborated on in this chapter. First, solubilities are different. In some cases, classes of compounds are more soluble in some nonaqueous solvents than they are in water. Second, the strongest acid that can be used in an aqueous solution is H30+. As was illustrated in Chapter 9, any acid that is stronger than H30+ will react with water to produce H30+. In some other solvents, it is possible to routinely work with acids that are stronger than H30+. Third, the strongest base that can exist in aqueous solutions is OH-. Any stronger base will react with water to produce OH-. In some nonaqueous solvents, a base stronger than OH - can exist, so it is possible to carry out certain reactions in such a solvent that cannot be carried out in aqueous solutions. These differences permit synthetic procedures to be carried out in nonaqueous solvents that would be impossible when water is the solvent. As a result, chemistry in nonaqueous solvents is an important area of inorganic chemistry, and this chapter is devoted to the presentation of a brief overview of this area. 

Fig. 2. Overview of stability constants (logio-Ka, on the molar scale) for formation of calcium complexes in aqueous solution, at (or close to) 298 K and in ionic strengths in the region of 0.1-0.15 M.

In this chapter, we discuss first how the silver clusters relate to silver atoms and silver nanoparticles. Then we overview the formation of fluorescent silver clusters in aqueous solution, using silver salts as precursors and various scaffolds as stabilizers. Finally we discuss applications of silver clusters in fluorescent labeling of biological tissues, and their use as fluorescent probes for sensing of molecules. 

Abiotic transformation of contaminants in subsurface natural waters result mainly from hydrolysis or redox reactions and, to lesser extent, from photolysis reactions. Complexation with natnral or anthropogenic ligands, as well as differential volatilization of organic compounds from multicomponent hquids or mixing with toxic electrolyte aqueous solutions, may also lead to changes in contaminant properties and their environmental effects. Before presenting an overview of the reactions involved in contaminant transformations, we discuss the main chemical and environmental factors that control these processes. 

B. Overview of Transient Grating Results 1. MbCO in Aqueous Solutions... 

The purpose of this chapter is to present a brief overview of the geochemistry of mineral surfaces, including their (1) dissolution mechanisms, (2) development of electrical charge when in contact with aqueous solutions, and (3) uptake of aqueous cations and anions, and to discuss some of the factors that control their chemical reactivity, including (1) defect density, (2) cooperative effects among adsorbates,... 

In Part II, we deal with various electrochemical techniques and show how they are applicable in non-aqueous solutions. In this chapter, we give an overview of electrochemical techniques, from the principles of basic techniques to some recent developments. It will help readers from non-electrochemical fields to understand the latter chapters of Part II. Many books are available to readers who want to know more about electrochemical techniques [1], In particular, the excellent book by Bard and Faulkner [la] provides the latest information on all important aspects of electroanalytical chemistry. 

Polar organic solvents with electrolytes such as sodium p-toluenesulfonate are compatible with capillary electrophoresis. Background electrolyte need not be an aqueous solution. [P. B. Wright, A. S. Lister, and J. G. Dorsey, Behavior and Use of Nonaqueous Media Without Supporting Electrolyte in Capillary Electrophoresis and Capillary Electrochromatography, Anal. Chem. 1997, 69, 3251 I. E. Valko, H. Siren, and M.-L. Riekkola, Capillary Electrophoresis in Nonaqueous Media An Overview, LCGC 1997, 15, 560.]... 

Chapter HI relates to measurement of flow properties of foods that are primarily fluid in nature, unithi.i surveys the nature of viscosity and its relationship to foods. An overview of the various flow behaviors found in different fluid foods is presented. The concept of non-Newtonian foods is developed, along with methods for measurement of the complete flow curve. The quantitative or fundamental measurement of apparent shear viscosity of fluid foods with rotational viscometers or rheometers is described, unithi.2 describes two protocols for the measurement of non-Newtonian fluids. The first is for time-independent fluids, and the second is for time-dependent fluids. Both protocols use rotational rheometers, unit hi.3 describes a protocol for simple Newtonian fluids, which include aqueous solutions or oils. As rotational rheometers are new and expensive, many evaluations of fluid foods have been made with empirical methods. Such methods yield data that are not fundamental but are useful in comparing variations in consistency or texture of a food product, unit hi.4 describes a popular empirical method, the Bostwick Consistometer, which has been used to measure the consistency of tomato paste. It is a well-known method in the food industry and has also been used to evaluate other fruit pastes and juices as well. 

Adsorption technology is frequently used as a robust technique to remove water-soluble ions that are detrimental to human health from aqueous solutions, especially when these ions exist in low concentrations. Thus, a lot of studies have been reported in literature on the use of various adsorbents for fluoride removal from drinking water. The studies have mainly been motivated by the need to have alternative adsorbents that are low in cost, have local availability, require little processing and are superior in performance. Synthetic adsorbents have good capacities for fluoride but are always expensive, while natural materials that are available in large quantities or certain wastes from agricultural or industrial concerns may potentially be low-cost materials. An overview of some of the adsorbents that have been reported in literature over the last two decades are given below. 

W. P. M. van Swaaij, On the kinetics between CO2 and alkanolamines both in aqueous and non-aqueous solutions. An overview, Chem. Eng. Commun., 1996, 144,113-158. 

Consequently, there is an increasing interest in alternative (or additional) electrolyte systems in which the above limitations can be removed. Providing the answers to the above limitations of aqueous solutions and the study, matching, and classification of alternative/additional electrolyte systems is the essence of nonaqueous chemistry. An overview of this branch of modern electrochemistry should include the presentation and classification of the important nonaqueous electrolyte systems, indicating their basic features, advantages, and limitations, as well as a short review of their typical applications. 

Most of the thermodynamic studies have been performed in aqueous solutions as the cycles and their derivatives are first of all ligands for complexation of water-soluble metal ions. Numerous compounds have been studied and, therefore, only a general overview of trends is given. More information can be find in commercial databases such as NIST Standard Reference Database 46 (Critically Selected Stability Constants of Metal Complexes) or The IUPAC Stability Constants Database (SC-Database) or in reviews <2005PAC1445> (critically evaluated data for DOTA 3 and TETA 4), <1999CCR97> (protonation constants of polyamines) and <2000CCR309> (protonation constants of polyamino-polycarboxylic acids). Overall basicity of the ligands is mostly the main determinant for values of stability constants of metal complexes. 

Research dealing with the atomic structure and charge distribution at crystal surfaces is a modern and fast-developing field. Metal and semiconductor surfaces show many interesting features, and this is certainly also the case for electrochemical interfaces, that is, metal (or semiconductor)/(aqueous) solution interfaces. This section is not intended to give a comprehensive overview of surface and interfacial... 

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