Some properties of aqueous solutions

When electrolyte solutions are subjected to such measurements, abnormal results are obtained. When substances like sodium chloride or magnesium sulphate are examined, the depression of freezing point or the elevation of boiling point is about twice that calculated from the relative molecular mass, with calcium chloride or sodium sulphate these quantities are three times those expected. Keeping in mind what has been said above, we can say that the number of particles in the solution of sodium chloride or magnesium sulphate is twice the number of molecules present, while in the case of calcium chloride or sodium sulphate there are three particles present for each molecule. 

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We now consider briefly a few examples of the evidence for structural transitions as reflected by anomalous temperature dependencies in some properties of aqueous solutions. 

Abstract Natural and synthetic polyelectrolytes have acquired notable importance in recent years due to their increasing application in different areas. One of these is downstream process methods which include the recovery, separation, concentration and purification of target enzymes from their natural sources. Polyelectrolytes interact with proteins to form soluble or non-soluble complexes. The interaction is driven by experimental variables of media such as pH, protein isoelectrical value, polyelectrolyte pKa, ionic strength and the presence of salts. The concentration of polyelectrolytes necessary to precipitate a protein completely is of the order of 10 " - 10 % p/v. Precipitation of protein by PE is a novel technique integrating clarification, concentration and initial purification in a single step. This chapter presents some properties of aqueous solutions of natural and synthetic PE as a tool to use them in the protein downstream process. 

This chapter presents some properties of aqueous solutions of natural and synthetic PE as a tool to use them in the protein downstream process. 

The second group of citations identifies compilations of numerical data. Additional specialized tables can also be found in some of the references listed in the third and fourth groups. References (13) and (14) are the last two volumes of a four volume compilation of properties of mixtures prepared by J. Timmermans. They contain a large compilation of various properties of aqueous solutions collected from all the previous literature. They are neither complete nor selective, however. 

Jones, W.J. and Speakman, J.B. Some physical properties of aqueous solutions of certain pyridine bases, J. Am. Chem. Soc., 43 1867-1870, 1921. 

Other properties of aqueous solutions where discontinuities were observed were molar volumes, heat capacities and viscosities.210-212 From all these pieces of evidence, the general opinion was that n in [M(H20) ]3+(aq) was nine for the lighter lanthanide ions, but eight for the heavier,213 though some workers were of the opinion that n did not change along the series.214 Solution X-ray studies have provided evidence for an average coordination number of 8.9 for Nd3+(aq),215 while neutron diffraction supports a value of 8.5 for the same ion.216... 

The predominant oxidation stale of the element is (V). There is some evidence that the (IV) state is obtained under certain reduction conditions. When the pentapositive form is not in the form of a complex ion it may exist in solution as PaC>2+. The compounds are very readily hydrolyzed in aqueous solution yielding aggregates of colloidal dimensions, thus showing marked similarity to niobium and tantalum in this respect. These properties play a dominant role in the chemical properties of aqueous solution, because the element is so easily removed from solution by hydrolysis and adsorption Protactinium coprecipilates with a wide variety of substances, and it seems likely that the explanation for this lies in the hydrolytic and adsorptive behavior. 

An understanding of equilibrium phenomena in naturally occurring aqueous systems must, in the final analysis, involve understanding the interaction between solutes and water, both in bulk and in interfacial systems. To achieve this goal, it is reasonable to attempt to describe the structure of water, and when and if this can be achieved, to proceed to the problems of water structure in aqueous solutions and solvent-solute interactions for both electrolytes and nonelectrolytes. This paper is particularly concerned with two aspects of these problems—current views of the structure of water and solute-solvent interactions (primarily ion hydration). It is not possible here to give an exhaustive account of all the current structural models of water instead, we shall describe only those which may concern the nature of some reported thermal anomalies in the properties of water and aqueous solutions. Hence, the discussion begins with a brief presentation of these anomalies, followed by a review of current water structure models, and a discussion of some properties of aqueous electrolyte solutions. Finally, solute-solvent interactions in such solutions are discussed in terms of our present understanding of the structural properties of water. 

It is much easier to demonstrate the existence of the kinks in the properties of aqueous solutions than in the properties of pure (bulk) water. The kinks do, however, seem to occur in the properties of both. For this reason, it is believed that the kinks (at least in dilute solutions) owe their existence to some phenomena associated with the structure of water itself and that the existence of the kinks in aqueous solutions are caused by the persistence of some particular structural features of pure water, even in the presence of ionic solutes. 

We have described several properties of aqueous solutions, some of which appear anomalous. It is now appropriate to discuss briefly what bearing these observations have on the degree and nature of involvement of the water structure in ion hydration. Specifically, are the observed concentration-dependent anomalies determined by the nature of the hydrated structures or are they manifestations of structural changes, induced by the ions, in the pure solvent The information which we have discussed also bears on the question of which model of hydration is most likely to be correct—the Frank-Wen (48) model or that of Samoilov (115). Some anomalies are amazingly abrupt. Vaslows occur over rather narrow concentration ranges, and those observed by Zagorets, Ermakov and Grunau are even sharper. Sharp transitions could be ex-... 

Some important physical properties of aqueous solutions of hydrogen peroxide are presented in Tab. 6-3. The toxicological properties and occupational health risks related to H2O2 are briefly summarized below (Ulhnann s, 1989) ... 

Most of the structural and dynamic studies in solutions have been carried out at ambient temperature and atmospheric pressure or not far from it. An increasing number of papers is devoted to supercooled [16-19] and glassy [18,20,21] water and solutions as well as to studies of water [22] and of aqueous solutions [23,24] at high temperature and/or pressure. Computer simulation methods are very flexible and are suitable for various studies at almost any thermodynamic conditions, and therefore a new strategy of the research can be established easily simulations may predict some properties of the solutions at conditions which can be later verified when the appropriate experimental conditions become available. 

Solutions are usually classified according to their physical state, as solid, liquid, or gaseous. The physical state of a solution is determined by the solvent. Many alloys are solid solutions of one metal dissolved in another. For example, brass, which is used to make musical instruments and many other objects, is a solution of copper and zinc. Air is a gaseous solution containing nitrogen, oxygen, and other gases. Carbon dioxide (a gas), alcohol (a liquid), and salt (a solid) each dissolve in water (a liquid) to form liquid solutions. Water is the most common solvent in the laboratory and in many fields. Water solutions are known as aqueous solutions. Because they are so important, in this section we will concentrate on the properties of aqueous solutions. Some solutions and their compositions are illustrated in Table 1. 

TABLE 6.1 Properties of Aqueous Solutions of Some Polymers... 

PEA/ECK] Pearce, J. N., Eckstrom, H. C., The vapor pressures and some thermodynamic properties of aqueous solutions of nickel chloride at 25 C, J. Phys. Chem., 41, (1937), 563-567. Cited on pages 128, 423. 

Fig. 4 Some properties of aqueous surfactant solutions related to CMC.

In this chapter, we shall survey some of the outstanding properties of pure water in the gaseous, liquid, and solid phases. We shall discuss only equilibrium thermodynamic quantities. Properties of aqueous solutions are deferred to Chapters 3 and 4. 

Thus, the unique temperature dependence of the volume of water is due to the unique packing of water molecules in such a way that an open local structure is correlated with large (negative) binding energy. This unique feature of the interaction has been built in the model of Sec. 2.5 to show a negative thermal expansion coefficient in a one-dimensional system. We shall also see in Chapter 3 that this unique property is also responsible for some outstanding properties of aqueous solutions of non-polar solutes. 

We conclude this section with a general comment on interstitial models. The study of such models is useful and quite rewarding in providing us insight into the possible mechanism by which water exhibits its anomalous behavior. One should be careful not to conclude that the numerical results obtained from the model are an indication of the extent of the reality of the model. It is possible, by a judicious choice of the molecular parameters, to obtain thermodynamic results which are in agreement with experimental values measured for real water. Such agreement can be achieved by quite different models. The important point is not the quantitative results of the model but the qualitative explanation that the model offers for the various properties of water. We shall use the same model in Sec. 3.6 to explain some aspects of aqueous solutions of simple solutes. 

In this section, we introduce what is essentially an equivalent model to the one described in Sec. 2.5.2. This model, referred to as the primitive cluster model, has several features that make it more useful in the study of the molecular mechanism underlying the anomalous behavior of liquid water and aqueous solutions. For water, as we shall see below, the two models provide essentially the same results. However, with the cluster model, we can get a deeper insight into the mechanism underlyingthe anomalies of water, namely the structural changes (here, essentially the change in the cluster-size distribution) in the liquid that lead to the anomalous behavior. As we shall see in Sec. 3.9, the cluster model is also more convenient for the study of some of the most outstanding properties of aqueous solutions of simple solutes. 

The theoretical understanding of dilute aqueous solutions has lagged behind that for pure water. However, because of their interest and importance, there has been significant progress in the understanding of these systems. Some of the outstanding properties of aqueous solutions of inert molecules were known in the 1930s. These will be reviewed in Sec. 3.2. 

In this section, we survey some of the outstanding properties of aqueous solutions of simple non-polar solutes such as argon, methane, and the like. [For an extensive review, see Battino and Clever (1966), Wilhelm and Battino (1973), Wilhem (1977), and Franks, Volume II 1973a.] The solubility of such solutes, as measured by the Ostwald absorption coefficient, is markedly smaller in water than in a typical organic liquid. (By typical or normal organic liquids, we mean alkanes, alkanols, benzene and its simple derivatives, etc.)... 

Some general comments regarding the application of the SPT to water are now in order. First, the SPT was originally devised for treating a fluid of hard spheres or simple non-polar fluids. The extension of the theory to complex fluids such as water is questionable. Second, the SPT employs an effective diameter of the solvent as the only molecular parameter. It is very likely that this diameter is temperature dependent. It is not clear, however, which kind of temperature dependence should be assumed for aitj. [This topic was discussed by Ben-Naim and Friedman (1967) and Pierotti (1967).] Finally, we stress again that the SPT is not a pure molecular theory. Even if it can predict the properties of aqueous solutions of gases, it is still incapable of providing an explanation of these properties. This is an inherent drawback of the theory since it cannot tell us why aqueous solutions behave in such a peculiar way as compared with other fluids. 

Some remarks on the rare earths by a Fifty-Year student of the subject, in Proc. 11th Rare Earth Research Conference, Traverse City, MI, October 7-10, 1974, Vol. 1, pp. 266-277. with A. Habenschuss, A survey of some properties of aqueous rare earth salt solutions. I. Volume, thermal expansion, Raman spectra and x-ray diffraction, in Proc. 11th Rare Earth Research Conference, Traverse City, Ml, October 7 10, 1974, Vol. 2, p. 909. 

Various theoretical approaches to the study of the pure water and aqueous infinitely dilute solutions or dilute solutions of nonpolar solutes have been analyzed in the well known book by Ben-Naim (4b) and in some more recent papers of the same author (142). Chan et alii(143) have given a summary of the distinctive characteristic of the thermodynamic properties of aqueous solutions of non polar molecules with respect to the aqueous solutions of polar molecules and some suggestions about the way the properties of the aqueous solutions could be justified with an "ad hoc" molecular distribution function. 

In This Chapter, You Will Learn about some of the properties of aqueous solutions and about several different types of reactions that can occur between dissolved substances. You will also leam how to express the concentration of a solution and how concentration can be useful in solving quantitative problems. 

Habenschuss, A. and F.H. Spedding, 1974, A Survey of Some Properties of Aqueous Rare Earth Salt Solutions. I. Volume, Thermal Expansion Raman Spectra and X-ray Diffraction, in Haschke, J.M. and H.A. Eick, eds., Proceeding.s of the Eleventh Rare Earth Research Conference, U.S. Atomic Energy Commission CONF-741002-P2 (National Technical Information Service, Springfield), pp. 909-918. 

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