Properties of the Solution

The properties of solutions have been extensively studied, and it has been found that they can be correlated in large part by some simple laws. These laws and some descriptive information about solutions are discussed in the following sections. 

In Chapter 2 a phase vas defined as a homogepeous part of a system, separated from other parts by physical boundaries. A solution is a phase which consists of two or more molecular species which are not readily interconvertible. These are called its components. Air is a gaseous solution of nitrogen, oxygen, carbon dioxide, water vapor, and the noble gases. Carbonated water is a liquid solution of water and carbon dioxide. (It contains other molecular species also—-HXO3,, HCO.j —but since these are readily convertible into water 

Gaseous hydrogen fluoride contains several molecular species, HF, H Fo, H3F3, etc. but since these are readily interconvertible it 

If one component of a solution is present in larger amount than the others, it may be called the solvent the others are called solutes. 

Example 1. A solution is made by dissolving 64.11 g of Mg(N03)2 6H0O in water enougli to bring the volume to 1 1. Describe the solution. 

In Chapter 1 a solution was defined as a homogeneous material that does not have a definite composition. 

The concentration of a solute is often expressed as the number of grams per 100 g of solvent or the number of grams per liter of solution. It is 

It is worth noting that a 1 M aqueous solution cannot be made up accurately by dissolving one mole of solute in 1 liter of water, because the volume of the solution is in general different from that of the solvent. Nor is it equal to the sum of the volumes of the components for example, 1 liter of water and 1 liter of alcohol on mixing give 1.93 liters of solution there occurs a volume contraction of 3.5%. There is no reliable way of predicting the density of a solution tables of experimental values for important solutions are given in reference books. 

1 For a review of the properties of ideal solutions, sec J. H. Hildebrand, lability of Non-electrolytes, 2nd ed., 1036, Chapter II. 

This expression will hold for any solution, but in the special case of an ideal solution, / // is equal to Ni, the mole fraction of that constituent, by equation (34.1). Since the mole fraction, for a mixture of definite composition, is independent of the temperature, it follows that for an ideal solution jH — Hi must be zero, i.e., and Rt are identical. Consequently, the partial molar heat content of any constituent of an ideal solution is equal to the molar heat content of that substance in the pure liquid state H°). As a result, equation (26.6), which for heat contents takes the form 

The total heat content H of the mixture is thus equal to the sum of individual heat contents of the pure liquid constituents hence, there is no heat change upon mixing the components of an ideal solution. In this respect, therefore, an ideal liquid solution resembles an ideal gas mixture ( 30d). 

By differentiating ln/ and In/P with respect to pressure, at constant temperature and coihposition, utilizing equations (29.7) and (30.17), and adopting a procedure similar to that given above, it can be readily shown that 

Solubility refers to the amount of solute that can dissolve in a solvent at a given temperature. The like-dissolves-like rule summarizes the fact that solutions form when solute and solvent have similar types of intermolecular forces. 

A solution is saturated when the maximum amount of solute has dissolved at a given temperature at that point, excess solute and dissolved solute are in equilibrium. Solubility is related to conditions  

The concentration of a solution can be expressed in different terms (molarity, molality, parts by mass, parts by volume, and mole fraction). Because a concentration is a ratio involving mass, volume, and/or amount (mol), the various terms are interconvertible. 

The physical properties of a solution differ from those of the solvent. These properties (vapor-pressure lowering, boiling-point elevation, freezing-point depression, and osmotic pressure) are called cofliga-tive because they depend on the number, not the chemical nature, of the dissolved particles. In salt solutions, interactions among ions cause deviations from expected properties. 

Heats of Solution and Solution Cycles Heats of Hydration 

1 Types of Solutions Intermolecular Forces and Solubility IntermoleciJar Forces h Solution Liquid Solutions 

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UNIFAC was built on the framework of a contemporary model for correlating the properties of solutions in terms of pure-component molecular properties and fitting parameters, viz. UNIQUAC (the universal quasi-chemical) model... 

Systematic studies67) to determine the properties of solutions of the obtained graft copolymers showed that graft copolymers containing stiff main chains (PAA,... 

G.8 A student investigating the properties of solutions containing carbonate ions prepared a solution containing 8.124 g of Na2C03 in a flask of volume 250.0 mL. Some of the solution was transferred to a buret. What volume of solution should be dispensed from the buret to provide... 

Why Do We Need to Know This Material In earlier chapters, we investigated the nature of the solid, liquid, and gaseous states of matter in this chapter, we extend the discussion to transformations between these states. The discussion introduces the concept of equilibrium between different phases of a substance, a concept that will prove to be of the greatest importance for chemical and biochemical transformations. We also take a deeper look at solutions in this chapter. We shall see how the presence of solutes is used by the body to control the flow of nutrients into and out of living cells and how the properties of solutions are used by oil companies to separate the components of petroleum. 

Colligative properties can be sources of insight into not only the properties of solutions, but also the properties of the solute. For example, acetic acid, CH.COOH, behaves differently in two different solvents, (a) The freezing point of a 5.00% by mass aqueous acetic acid solution is — l.72°C. What is the molar mass of the solute Explain any discrepancy between the experimental and the expected molar mass, (b) The freezing-point depression associated with a 5.00% by mass solution of acetic acid in benzene is 2.32°C. Whar is the experimental molar mass of the solute in benzene What can you conclude about the nature of acetic acid in benzene ... 

Products for personal care are big business Americans spend close to 12 billion annually on shampoos, conditioners, and styling gels. These products rely on intermolecular forces for their effectiveness. Shampoos, in particular, interact with water in ways that we can understand by knowing the properties of solutions. 

There are several attractive features of such a mesoscopic description. Because the dynamics is simple, it is both easy and efficient to simulate. The equations of motion are easily written and the techniques of nonequilibriun statistical mechanics can be used to derive macroscopic laws and correlation function expressions for the transport properties. Accurate analytical expressions for the transport coefficient can be derived. The mesoscopic description can be combined with full molecular dynamics in order to describe the properties of solute species, such as polymers or colloids, in solution. Because all of the conservation laws are satisfied, hydrodynamic interactions, which play an important role in the dynamical properties of such systems, are automatically taken into account. 

In studying the properties of solutions of substances such as HC1 and HN03, Arrhenius was led to the idea that the acidic properties of the compounds were due to the presence of an ion that we now write as H30+ in the solutions. He therefore proposed that an acid is a substance whose water solution contains H30+. The properties of aqueous solutions of acids are the properties of the H30+ ion, a solvated proton (hydrogen ion) that is known as the hydronium ion in much of the older chemical literature but also referred to as the oxonium ion. 

A great many of the difficulties (and sometimes the misunderstandings) arise from point (c). It is however important to notice that the APM describes the properties of solutions as finite differences between suitable composition-dependent averages and the properties of the pure components. Series expansions in powers of 6, p, 6, and a were introduced afterwards for the purpose of qualitative discussion and comparison with other treatments, e.g., the theory of conformal solutions.34>85>36 They introduce artificial difficulties due to their slow convergencef which have nothing to do with the physical ideas of the APM. Therefore expansions of this type should be proscribed for all quantitative applications one should instead use the compact expressions of the excess functions. 

Some years ago, Kamlet and Taft embarked upon a study of how solvents influence the properties of solutes, focusing initially upon the effects of hydrogen bonding upon electronic transitions.184185 This led eventually to an empirical relationship between a spectroscopic property X of a given solute, e.g., the position or intensity of a peak, and certain solvent parameters, a, p and it 186... 

Some of the properties of solutions are dependent upon the chemical and physical nature of the individual solute. However, there are solution properties that depend only on the number of solute particles and not their identity. These properties are colligative properties and they include ... 

A proper understanding of the properties of solutions of electrolytes begins with that of sodium chloride, the common salt. It is a typical example of a strong electrolyte and its characteristics in the solid state and in the dissolved state in aqueous... 

Sander et al. [63] investigated the effect of microparticulate silica pore size on the properties of solution-polymerized Cig stationary phases and observed both an increase in bonding density and shape recognition for wider pore (>120 A) silica. A size-exclusion mechanism was proposed, in which the reaction of the silane polymer on the surface is enhanced for wide pores and reduced for narrow pores. Polymeric Ci8 phases prepared on substrates with narrow pores exhibited monomeric-like chromatographic properties. This effect may be the result of an increase in competitive surface linkage with the less sterically hindered monomers that coexist with the bulkier oligomers that have polymerized in the reaction solution (Figure 5.13). 

The parameters AVg (acidity), AVg (basicity), pK, and Zo represent properties of solute in the bulk solution phase. If reverse osmosis separation is governed by the property of solute in the membrane-solution interface, the existence of unique correlations between data on reverse osmosis separations and those on the above parameters, means that the property of solute in the bulk solution phase and the corresponding property of solute in the membrane-solution interface are also uniquely related. This leads one to the development of interfacial free energy parameters (-AAG/RT) for both nonionized solute molecules and dissociated ions in solution for reverse osmosis systems where water is preferentially sorbed at the membrane-solution interface. 

Kaufman (1968b) also made it clear that the use of more realistic descriptions, such as sub-regular solution models, would necessitate the determination of many more parameters and thought that "Until such time as our knowledge of solution theory and the physical factors which control the properties of solutions might permit these parameters to be determined, it is better to continue with a simpler model. This conclusion was of course also conditioned by the limited computer memory available at the time, which prevented the use of more complex models with the subsequent increase in number of parameters which they entailed. 

The challenges involved in the material properties of PPC relate to its thermal features, i.e., its thermal decomposition, and the glass transition temperature (Tg) of about body temperature of the otherwise amorphous polymer. These have implications for processing and application of the material. This review will discuss consecutively the thermal, viscoelastic, and mechanical properties of PPC and the experiences in processing PPC and its composites. The properties of solutions of PPC will also be presented, and the biodegradabUity and biocompatibility discussed. Spectroscopic properties will not be discussed. Further information on NMR data can be found in the following references [2, 10-12]. A t3 pical spectrum is shown in Fig. 2 [13]. 

The properties of solutions of macromolecular substances depend on the solvent, the temperature, and the molecular weight of the chain molecules. Hence, the (average) molecular weight of polymers can be determined by measuring the solution properties such as the viscosity of dilute solutions. However, prior to this, some details have to be known about the solubility of the polymer to be analyzed. When the solubility of a polymer has to be determined, it is important to realize that macromolecules often show behavioral extremes they may be either infinitely soluble in a solvent, completely insoluble, or only swellable to a well-defined extent. Saturated solutions in contact with a nonswollen solid phase, as is normally observed with low-molecular-weight compounds, do not occur in the case of polymeric materials. The suitability of a solvent for a specific polymer, therefore, cannot be quantified in terms of a classic saturated solution. It is much better expressed in terms of the amount of a precipitant that must be added to the polymer solution to initiate precipitation (cloud point). A more exact measure for the quality of a solvent is the second virial coefficient of the osmotic pressure determined for the corresponding solution, or the viscosity numbers in different solvents. 

The theoretical treatment of the hydrophobic effect is limited to pure aqueous systems. To describe chromatographic separations in RPC Horvath and Melander developed the solvophobic theory [47]. In this theory, no special assumptions are made about the properties of solute and solvent, and besides hydrophobic interaction electrostatic and other specific interactions are included. The theory has been valuable to describe the retention of nonpolar [48], polar [49], and ionizable [50] solutes in RPC. The modulation of selectivity via secondary equilibria (variation of pH, ion pair formation [51]) can also be described. On the other hand, it is not a problem to find examples of dispersive interactions in literature, e.g., separation of carotinoids with a long chain (C30) RP gives a higher selectivity compared to standard RP C18 cyclohexanols are preferentially retarded on cyclohexyl-bonded phases compared to phases with linear-bonded alkyl groups. 

As a reactant, solvents frequently react with solntes. Snbstances that are insoluble in one solvent can dissolve in another by reacting with it. Thus, bone (hydroxyapatite, CasCOHXPOds) is insoluble in most solvents bnt dissolves in 100% sulfuric acid, with protonation of the phosphate. When any solnte is dissolved in a solvent, possible solute-solvent reactions must always be considered. Solvents can be used to modify the properties of solutes. Nitric acid dissolved in water behaves quiet differently to nitric acid dissolved in concentrated snlfnric acid. 

The problem of understanding the processes which occur when a gaseous ion is put into a solvent such as water has commanded the attention of chemists for more than 80 years. It is a key to the understanding of the properties of solutions and is of far reaching technological and theoretical importance. If the solvent is made up of two or more components, preference may be shown for one of these components by the cations, anions, or both. This is the problem of preferential solvation or of solvent-sorting in the immediate vicinity, the co-spheres (i), of the ions. 

These partial molar quantities are the key quantities used to describe the properties of solutions. 

In the following, we shall discuss the influence of low molecular weight electrolytes (salt) on the properties of solutions of the PPP polyelectrolytes. 

Surfactants are frequently used in detergents and food products to alter the properties of solution interfaces, mediating between immiscible phases because of their hydrophobic and hydrophilic moieties. The addition of surfactants increases the concentration of hydrophobic compounds in the water phase by solubilization or emulsification above a specific threshold, the critical micellar concentration (CMC), where surfactant molecules aggregate to micelles [130]. Two widely utilized nonionic surfactants, Tween 80 and Triton X-100, were evaluated in terms of enzyme interaction, by calculating the inactivation coefficient (kA) under static conditions. Concentrations lower than CMC were studied in order to avoid diffusional limitations in the interaction of the enzyme and the PAH in the micellar phase. The concentration 0.25 CMC was considered the most favorable for the enzyme, with Triton X-100 being the surfactant that led to the lowest inactivation coefficients for all the concentrations tested and was 2.5 times lower than kd in control experiment. 

One way of probing trends in either 8rAX or 5m AX is to examine the corresponding effects in either initial or transition states. Although it is not possible to examine the properties of transition states directly, these can often be estimated by measuring the properties of solutes which resemble postulated transition states. 

Analysis of solvent effects on activation parameters, 8m AX, requires information concerning the behaviour of solutes in aqueous mixtures. Although some such information has been published in recent years, a great deal more is certainly desirable. The division between the different classes of solvent mixtures (p. 283) has been made, however, because the properties of solutes in these mixtures also reflect this subdivision. Although interpretation of the changes in solute properties with change in solvent composition is not straightforward, we can nevertheless predict some of the trends to be expected. 

The complexity of the properties and structures of aqueous mixtures is not unexpectedly carried over to the properties of solutes in these TA mixtures. In reviewing the properties of some of these three component systems, we shall consider first apolar solutes and finally ionic solutes. 

Compared to the extensive information concerning the properties of solutes in TA mixtures, there is little information for this class of systems and most of it refers to acetonitrile + water mixtures. 

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