The Composition of Solutions

Acetic acid (HC2H302) exists in water mostly as undissociated molecules. Only a small percentage of the molecules are ionized. 

The reaction of NH3 in water. The NH4+ and OH- ions are formed by reaction of an NH3 molecule with an H20 molecule. 

Acetic acid is very different from the strong acids in that only about 1% of its molecules dissociate in aqueous solution (see Fig. 4.7). Thus, when 100 molecules of HC2H3O2 are dissolved in water, approximately 99 molecules of HC2H3O2 remain intact, and only one H+ ion and one C2H302 ion are produced. 

Because acetic acid is a weak electrolyte, it is called a weak acid. Any acid, such as acetic acid, that dissociates only to a slight extent in aqueous solution is called a weak acid. In Chapter 7 we will explore weak acids in detail. 

The most common weak base is ammonia (NH3). When ammonia is dissolved in water, it reacts as follows  

Chemical reactions often take place when two solutions are mixed. To perform stoichiometric calculations in such cases, we must know two things (1) the nature of the reaction, which depends on the exact forms the chemicals take when dissolved, and (2) the amounts of chemicals present in the solutions, usually expressed as concentrations. 

The concentration of a solution can be described in many different ways, as we will see in Chapter 11. At this point we will consider only the most commonly used expression of concentration, molarity hf), which is defined as moles of solute per volume of solution in liters  

A solution that is 1.0 molar (written as 1.0 M) contains 1.0 mole of solute per liter of solution. 

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Calculate the molarity of a solution prepared by dissolving 11.5 g of solid NaOH In enough water to make 1.50 L of solution. 

The solution is basic because OH ions are produced. Ammonia is called a weak base because the resulting solution is a weak electrolyte that is, very few ions are formed. In fact, in a solution containing 0.1 mole of NH3 per liter, for every 100 molecules of NH3 originally dissolved, only one NH4+ ion and one OH ion are produced 99 molecules of NH3 remain unreacted (Fig. 4.9). The double arrow indicates the reaction can occur in either direction. 

Nonelectrolytes are substances that dissolve in water but do not produce any ions, as shown in Fig. 4.4(c). An example of a nonelectrolyte is ethanol (see Fig. 4.3 for the structural formula). When ethanol dissolves, entire C2H5OH molecules are dispersed in the water. Since the molecules do not break up into ions, the resulting solution does not conduct an electric current. Another common nonelectrolyte is table sugar (sucrose, C12H22O11), which is very soluble in water but which produces no ions when it dissolves. The sucrose molecules remain intact. 

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System in which the solid phases consist of the pure components and the components are completely miscible in the liquid phase. We may now conveniently consider the general case of a system in which the two components A and B are completely miscible in the liquid state and the solid phases consist of the pure components. The equilibrium diagram is shown in Fig. 1,12, 1. Here the points A and B are the melting points of the pure components A and B respectively. If the freezing points of a series of liquid mixtures, varying in composition from pure A to pure B, are determined, the two curves represented by AC and BC will be obtained. The curve AC expresses the compositions of solutions which are in equilibrium, at different temperatures, with the solid component A, and, likewise, the curve BC denotes the compositions... 

By analogy with the mechanisms of nitration in other media, and from a knowledge of the composition of solutions of acetyl nitrate in acetic anhydride, the following may be considered possible nitrating species in these solutions ... 

We have already come across one example of the qualitative application of acid-base titrimetry in assigning the forms of alkalinity in waters (see Example 9.5). This approach is easily extended to other systems. For example, the composition of solutions containing one or two of the following species... 

The composition of solutions that are used for washing and stripping of extracts is also different and is adjusted for each specific case however, some common conditions can be noted. It is recommended that the extract obtained following collective extraction, which contains both tantalum and niobium, be washed (scrubbed) using sulfuric acid solutions that contain at least 6 mol per liter of H2SO4. Collective stripping of the elements, on the other hand, can be... 

Equilibria considerations on solution-grown zinc chalcogenide compounds have been put forward by Chaparro [28] who examined the chemical and electrochemical reactivity of solutions appropriate for deposition of ZnS, ZnSe, ZnTe (and the oxide ZnO) in order to explain the results of recipes normally used for the growth of such thin films. The author compared different reaction possibilities and analyzed the composition of solutions containing zinc cations, ammonia, hydrazine, chalcogen anions, and dissolved oxygen, at 25 °C, by means of thermodynamic diagrams, applicable for concentrations usually employed in most studies. 

The pressure above a solution relates to the composition of solution, according to Henry s law see Section 5.6. 

Generally, the activity coefficient y depends on the composition of solution. In the ranges of our narrow purposes of investigations of the macromolecules chemical potential conformation term influence on the osmotic pressure of polymeric solutions we will be neglect by the change of y lying y = const in all range of the macromolecules concentrations into solution. This permits to write... 

The ion selectivity of a membrane can be established by measuring the potential difference between two identical reference electrodes. One electrode is immersed in the specimen solution, the other in a reference solution, and the membrane is interposed between them. The composition of solution 2 is constant, and, if both solutions contain monovalent ions, the ion-exchange process can be described as follows ... 

If the composition of solution 2 is assumed to remain unchanged, the above reduces to ... 

Furthermore, if the overall concentration of positive charges is the same on both membrane surfaces and if the composition of solution 2, which contains cations of the I2+ sort only, remains constant, then ... 

The composition of aqueous solutions of D-arahino-2-hexulose (d-fructose) has also been studied by laser-Raman spectroscopy.45 (The composition of solutions of D-fructose appears to have been determined by more methods, and more often, than that of any other sugar.20)... 

Before discussing the composition of solutions of individual sugars, it will be instructive to look at the relative stabilities of the various forms of the sugars. These considerations will give a general overview, and also provide explanations for some of the results. 

The equilibrium compositions of aqueous solutions of some aldoheptoses are listed in Table III. Because the additional carbon atom in the side chain does not introduce additional steric interactions, the composition of solutions of heptoses is similar to that of the homomorphous hexoses, with only one exception, namely, n-glycero-n-ido-heptose, 92 a-D-Idopyranose in solution is a mixture of the 4Ci and 1C4 conformant) S. J. Angyal and R. J. Beveridge, Carbohydr. Res., 65 (1978) 229-234. 

The composition of solutions of the 2-heptuloses has been determined, and discussed, by Angyal and Tran.92 These ketoses are different from other reducing sugars inasmuch as there are two hydroxymethyl side chains attached to the pyranose ring. In the a-pyranose form, they are cis to each other and will therefore both be equatorial in the preponderant chair form. In the / -pyranose, however, one or other of the hydroxymethyl groups has to be axial and, in consequence, the / anomers are disfavored in only one solution (that of the altro isomer) was the yS-pyra-nose detected in the 13C-n.m.r. spectrum.92... 

Whereas the composition of solutions of the unsubstituted aldoses and ketoses has been systematically investigated, very few studies have been conducted on substituted and on derived sugars, such as amino sugars,... 

Now that we have an idea of the composition of solutions of strong electrolytes, we can move on to consider what happens when we pour one solution into another. A solution of sodium chloride consists of hydrated Na+ cations and hydrated Cl- anions. Similarly, a solution of silver nitrate, AgN03, consists of hydrated Ag+ cations and hydrated NO, anions. When we mix these two aqueous solutions, we immediately get a white precipitate, a cloudy, finely divided solid deposit. Analysis shows that the precipitate is silver chloride, AgCl, an insoluble white solid (Fig. 1.6). The colorless solution remaining above the precipitate in our example contains hydrated Na+ cations and hydrated N03 anions. These ions remain in solution because sodium nitrate, NaNO is soluble in water. 

Measures of the composition of solutions of a solute B (2-bromoethanol, d = 1.7629 g cm"3 at 20°C) in a solvent A (water, d = 0.9982 g cm 3 at 20°C) against the mass fraction WB XB is the mole fraction and cpB is the volume fraction (assuming negligible volume change on mixing) (left hand ordinate) and mB is the molality and CB is the molarity (right hand ordinate). 

THE COMPOSITION OF SOLUTIONS SATURATED WITH CALCIUM HYDROGEN PHOSPHATES.3... 

We have just examined the effects of varying the composition of solutions at constant T and P we now consider the effect of varying the temperature. This situation is more complex in that the vapor pressure of the two species and the composition of the two phases, as well as the total pressure, are altered. This comes about because a rise in temperature, for example, will favor vaporization of the more volatile component, thereby enriching the gas phase and depleting the liquid phase of this component. Thus, all and all x (or PA) are altered, even though the overall system is closed, and even though no chemical reactions occur. An analysis of all these factors would be too complex to be of immediate use. We therefore impose the condition that the total pressure P be maintained... 

The formulation provided here has the great advantage that the standard chemical potential is now independent of the mode of specifying the composition of solutions. The standard state in each instance refers to that of pure i at temperature T and unit pressure. The price paid for this simplification is that the interrelations between ai(T,P,qi) and qt are now slightly more complex than those involving ai(T,P,qi) and qA when q - c,m. The at introduced in Eq. (3.6.3) will be termed the relative activity. Note that whereas ai(T,l,c ) and ai(T,l,m ) differ from unity, a1(T,l,q ) - 1 for all qi. Equations (3.6.3) also show explicitly that ai(T,P,xi) -ai(T,P,ci) = ai(T,P,mi) all have the same numerical values, independent of the composition units, whereas the corresponding... 

Kryukov P. A., Zhuchkova A. A., and Rengarten E. F. (1962) Change in the composition of solutions pressed from clays and ion exchange resins. Akademiia Nauk SSSR Earth Sci. Sect. 144, 167-169. 

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