Partial pressure Aqueous solutions, pure

The aqueous solubility of a gaseous compound is commonly reported for 1 bar (or 1 atm = 1.013 bar) partial pressure of the pure compound. One of the few exceptions is the solubility of 02 which is generally given for equilibrium with the gas at 0.21 bar, since this value is appropriate for the earth s atmosphere at sea level. As discussed in Chapter 3, the partial pressure of a compound in the gas phase (ideal gas) at equilibrium above a liquid solution is identical to the fugacity of the compound in the solution (see Fig. 3.9d). Therefore equating fugacity expressions for a compound in both the gas phase and an equilibrated aqueous solution phase, we have ... 

The partial pressure p, canbe obtained from Raoult s law which relates the partial pressure of wafer vapour above the surface of an aqueous solution held at a constant temperature, the mole fraction of wafer in the solution and the pure component vapour pressure of water, i.e. 

Deliquescence.—It sometimes happens that a salt that has been crystallized and spread in the air to dry absorbs water instead of losing it and in time passes again into solution. This may occur with anhydrous salts as well as with hydrates but not so frequently. This conduct is readily understood if it is remembered that the process of drying is always dependent upon the equilibrium between the aqueous vapor pressure of the material undergoing drying and the partial pressure of the water vapor in the air. The vapor pressure of a salt solution is always lower than that of the pure solvent. When the solution is very concentrated, its vapor pres-... 

Table I and Figures 1-4 contain a wealth of information about the solubilization of benzene in aqueous surfactant micelles. Plots of K vs. Xg exhibit shallow minima in the case of the SDS solutions, and rather more pronounced minima for the CPC solutions. The plots of Tg vs. Xg show corresponding maxima, reflecting the fact that K and Yg are related reciprocally by K l/(TBcB ), where cB° is the monomer concentration of benzene in the aqueous phase at saturation. (The minimum in K and the maximum in Yg for the CPC solutions, shown in Figure 1, are not quite reached at the benzene concentrations attainable with the automated vapor pressure apparatus. The automated apparatus is restricted to operating at partial pressures less than about 70% of the vapor pressure of pure liquid benzene. However, the manual apparatus can be used for measurements almost to saturation, and results obtained with this apparatus show extrema in K and Yg at approximately X = 0.55.)...

Because of their rigid cell walls, large hydrostatic pressures can exist in plant cells, whereas hydrostatic pressures in animal cells generally are relatively small. Hydrostatic pressures are involved in plant support and also are important for the movement of water and solutes in the xylem and in the phloem. The effect of pressure on the chemical potential of water is expressed by the term VWP (see Eq. 2.4), where Vw is the partial molal volume of water and P is the hydrostatic pressure in the aqueous solution in excess of the ambient atmospheric pressure. The density of water is about 1000 kg m-3 (1 g cm-3) therefore, when 1 mol or 18.0 x 10-3 kg of water is added to water, the volume increases by 18.0 x 10-6 m3. Using the definition ofV,., as a partial derivative (see Eq. 2.6), we need to add only an infinitesimally small amount of water (dnw) and then observe the infinitesimal change in volume of the system (dV). We thus find that Vw for pure water is 18.0 x 10-6 m3 mol-1 (18.0 cm3 mol-1). Although Vw can be influenced by the solutes present, it is generally close to 18.0 x 10-6 m3 mol-1 for a dilute solution, a value that we will use for calculations in this book. 

Water molecules in an aqueous solution continually escape into a surrounding gas phase, and simultaneously water molecules condense back into the liquid phase, the two rates becoming equal at equilibrium. The gas phase adjacent to the solution then contains as much water as it can hold at that temperature and still be in equilibrium with the liquid. The partial pressure in the gas phase exerted by the water vapor in equilibrium with pure water is known as the saturation vapor pressure, P ,. 

The reaction of a strong solution of aqueous ammonia with the sulfide concentrate in a strongly agitated pressure vessel at a temperature between 160 and 190°F under an oxygen partial pressure of about 10 psi, either as pure oxygen or as compressed air, fulfills the optimal conditions for the above requirements. The iron present in the concentrate is oxidized to hydrated ferric oxide which, together with the silicates is insoluble in aqueous ammonia. The copper, nickel, and cobalt form their amines, while the sulfides are oxidized to sulfates, thiosulfates, and polythionates. 

In summary, thermodynamic models of natural water systems require manipulation of chemical potential expressions in which three concentration scales may be involved mole fractions, partial pressures, and molalities. For aqueous solution species, we will use the moial scale for most solutes, with an infinite dilution reference state and a unit molality standard state (of unit activity), l or the case of nonpolar organic solutes, the pure liquid reference and standard states are used. Gaseous species will be described on the partial pressure (atm — bar) scale. Solids will be described using the mole fraction scale. Pure solids (and pure liquids) have jc, = 1, and hence p, = pf. 

Initially, the vapor pressure measurements appear to be the most direct, but even here some assumptions are needed. The amount of alcohol in the micellar phase needs to be determined. To do this the difference in vapor pressure between a pure aqueous and a micellar solution is measured. If the ions of the surfactant salts out alcohol, the vapor pressure of pure water is not the correct comparison, and this could lead to lower partition coefficients. Thermodynamic data are well suited for model calculations, and both the models of DeLisi et al. ° ° and Hetu et al. fit the data well. Although in reasonable internal agreement, the partition coefficients calculated from partial molar volumes differ from those calculated from enthalpies the first is 927 or 944, the latter... 

Note that, forgetting about activity coefficients for the moment, we have arranged things rather conveniently, such that the activity of pure solids and liquids will be 1.0 (the mole fraction of a pure compound being 1.0) the activity of a solid solution component is its mole fraction the activity of a gas is (numerically equal to) its partial pressure and the activity of an aqueous solute is (numerically equal to) its molality. These are useful approximations for real systems, which can be improved by using the activity coefficients. Note that activities are always dimensionless, though we have not demonstrated this. 

The table also contains values of the Henry s Law constant which provides a measure of the partition of a substance between the atmosphere and the aqueous phase. Here is defined as the limit of / j/Cj as the concentration approaches zero, where is the partial pressure of the solute above the solution and is the concentration in the solution at equilibrium (other formulations of Henry s Law are often used see Reference 5). The values of k listed here are based on direct experimental measurement whenever available, but many of them are simply calculated as the ratio of the pure compound vapor pressure to the solubility. This approximation is reliable only for compounds of very low solubility. In fact, values of k found in the literature frequently differ by a factor of two or three, and variations over an order of magnitude are not unusual (Reference 5). Therefore the data given here should be taken only as a rough indication of the true Henry s Law constant, which is difficult to measure precisely. 

Dilute aqueous solutions of urea are not decomposed by boiling but if the solution be concentrated, or the boiling prolonged for a long time, the urea is partially decomposed into COi and NH>. The same decomposition takes place more rapidly and completely when a solution of urea is heated under pressure to 140° (284° F.). A pure aqueous solution of urea is not altered by exposure to filtered air. If urine be allowed to stand, putre-... 

Note that the concentration product of nitric acid and ammonia in equilibrium with a mixed sulfate-nitrate solution having a value of T = 0.5 is about one-half as high as that in equilibrium with a pure ammonium nitrate solution. The temperature dependence of the partial-pressure product for the aqueous mixed-salt case is similar to that of the pure salt. 

Carbon Monoxide. The facilitated transport of carbon monoxide by cuprous chloride in aqueous solution was first studied by Steigelroan and Hughes (j 8) and more recently by Smith and Quinn (J 9). Smith and Quinn found the cuprous ion to be very effective c2U"rier for carbon monoxide and increased the flux by two orders of magnitude over the purely diffusive case. The facilitation factor was measured as a function of carbon monoxide partial pressure, total copper concentration, and membrane thickness. Recently, Koval et al. (20) reported facilitated CO transport using a ferrous complex derived from the tetraimine macrocyclic ligand 2,3,9,10-tetramethyl-1,3,8,11-tetraazacyclo-tetradeca-1,3,8,10- tetraene(TIM) in benzoni-trile. They measured the kinetic and dlffusional constants and showed selectivity for CO over a variety of other gases. The experimental and mathematical procedures which they described can be used for any simple complexatlon reaction. 

This paper describes pure N2 permeation and CO2-N2 separation characteristics of ILM-s of pure water and aqueous 302 wt/wt K2CO3 solutions Immobilized in Celgard X-10 hollow fibers. Measurements were carried out over a wide range of applied pressure differences. The CO2 partial pressure difference was varied from about 40 cm Hg to 140 cm Hg while the N2 partial pressure difference was Increased from about 125 cm Hg to 425 cm Hg. The total applied pressure difference was varied between 140 to 550 cm Hg. Facilitated transport membranes of aqueous 3UZ wt/wt K2CO3 solution for the separation of CO2 from were utilized and the separation behaviors... 

In about 1886, Raoult discovered that substances have lower vapor pressures in solution than in pure form and that the freezing point of an aqueous solution decreases in proportion to the amount of a non-electrolytic substance dissolved. The ratio of the partial vapor pressure of substance i in solution to the vapor pressure of the pure substance (subscript 0 denotes the pure substance) is equal to the mole fraction x of i ... 

Take, for example, the case of a water-soluble substance. If the partial pressure of water vapour in the atmosphere is greater than the vapour pressure that would be exerted by a saturated aqueous solution of the pure substance at that temperature, water will be absorbed by the crystals. If, later, the atmospheric moisture content falls to give a partial pressure below the vapour pressure of the saturated solution, the crystals will dry out and bind together. Small fluctuations in atmospheric temperature and humidity, sufficient to bring about these changes, can occur several times in one day. 

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