Solute saturation vapor pressures

Solubility has cgs units of g/cm3 Pa, where pa is the solute partial pressure and p is the solute saturated vapor pressure at the temperature of the system. Note that at ambient temperature and pressure one can assume ideal gas behavior. Henry s constant for a solute in a polymer is a special solubility coefficient case where... 

An alternative method of data reduction was reported early in the history of gas chromatography by Hoare and Purnell (12-15 see refs. 16,17 for recent applications), who considered the dependence oTffie specific retention volume on the solute saturation vapor pressure pA. Thus, taking the view [now recognized to be naive (18) see later], that the observed mole fraction-based solute activity coefficient" can be decomposed into "athermal" and "thermal" components (19-22) v v-... 

In the second picture, an interfacial layer or region persists over several molecular diameters due to a more slowly decaying interaction potential with the solid (note Section X-7C). This situation would then be more like the physical adsorption of vapors (see Chapter XVII), which become multilayer near the saturation vapor pressure (e.g.. Fig. X-15). Adsorption from solution, from this point of view, corresponds to a partition between bulk and interfacial phases here the Polanyi potential concept may be used (see Sections X-7C, XI-1 A, and XVII-7). 

The solvent s activity can be determined by measuring the saturation vapor pressure above the solution. Such measurements are rather tedious and their accuracy at concentrations below 0.1 to 0.5M is not high enough to produce reliable data therefore, this method is used only for concentrated solutions. The activity can also be determined from the freezing-point depression or boiling-point elevation of the solution. These temperature changes must be ascertained with an accuracy of about 0.0001 K, which is quite feasible. This method is used primarily for solutions with concentrations not higher than 1M. 

When zirconium is saturated with oxygen in solid solution, the vapor pressure of zirconium monoxide is 50 to 100 times higher than that of pure zirconium. The R value of zirconium remains at 3 to 4 up to 5 at-% oxygen, and then decreases to the limiting value of... 

The solution requires the concentration of the heptane and toluene in the vapor phase. Assuming that the composition of the liquid does not change as it evaporates (the quantity is large), the vapor composition is computed using standard vapor-liquid equilibrium calculations. Assuming that Raoult s and Dalton s laws apply to this system under these conditions, the vapor composition is determined directly from the saturation vapor pressures of the pure components. Himmelblau6 provided the following data at the specified temperature ... 

If gas-liquid and gas-solid separations are dependent on the saturation vapor pressure of the chemical component undergoing equilibration (a) What is the expected effect when the temperature of the system is raised (b) If the system is a gas-liquid system sketch what a plot of log VT vs. 1 IT would look like including when the T is below the freezing point of the stationary phase, (c) Why might it be better to sample the vapor phase above a solution as a sample to determine trace materials in the solution ... 

The heat of vaporization for a sea salt solution boiling at the same temperature and at its own saturation vapor pressure, P2, is the difference between the enthalpy of the vapor per pound, HV2l and the enthalpy per pound of the water in the salt solution, Hl2. 

The equilibrium constants were obtained at the saturation vapor pressure, that is, at a pressure equal to the vapor pressure of water over the solution. 

Immersion in pure water must lead to the same result as in a saturated atmosphere. If water contains solutes, its vapor pressure decreases. The corresponding equilibrium concentration, linked to the water activity, is proportional to the water vapor pressure. In other words, the water equilibrium concentration is a decreasing function of the solute concentration salt water is less active than pure water. 

Figure 2.13 The effect of permeate pressure on the water flux through a silicone rubber pervaporation membrane. The arrows on the lower axis represent the saturation vapor pressures of the feed solution at the temperature of these experiments as predicted by Equation (2.79) [15]...

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 vapor pressure at equilibrium depends on the temperature and the solution, but it is independent of the relative or absolute amounts of liquid and vapor. When air adjacent to pure water is saturated with water vapor (100% relative humidity), the gas phase has the maximum water vapor pressure possible at that temperature — unless it is supersaturated, a metastable, nonequilibrium situation. This saturation vapor pressure in equilibrium with pure water (P ) increases markedly with temperature (Fig. 2-16) for example, it increases from 0.61 kPa at 0°C to 2.34 kPa at 20°C to 7.38 kPa at 40°C (see Appendix I). Thus, heating air at constant pressure and constant water content causes the relative humidity to drop dramatically, where... 

As solutes are added to the liquid phase and the mole fraction of water is thereby lowered, water molecules have less tendency to leave the solution. Hence, the water vapor partial pressure in the gas phase at equilibrium becomes less —this is one of the colligative properties of solutions that we mentioned earlier. In fact, adjacent to dilute solutions P at equilibrium depends linearly on the mole fraction of water (Nw) in the liquid phase. This is Raoult s law (also mentioned in Appendix IV). For pure water, Nw equals 1 and Pwv has its maximum value, namely P w> the saturation vapor pressure. 

Ideal solutions behave in accord with Raoult s Law, which relates the partial pressure of a solute vapor to the mole fraction of soiute in solution and the saturated vapor pressure of pure solute. Deviations from ideality can be accomodated by use of the activity coefficient such that... 

The model was shown to predict osmotic coefficients to within the experimental error for the determination of osmotic coefficients from saturated vapor pressure measurements. Activity coefficient calculations appeared to be consistent with the available data for mixed electrolyte solutions. 

Hydrothermal synthesis of a-alumina has been well studied. Since the hydro-thermal reaction of aluminum compound yields boehmite at relatively low temperatures (approximately 200°C), transformation of boehmite was examined and it was reported that more than 10 hours is required for complete conversion into a-alumina, even with a reaction at 445°C in a 0.1 N NaOH solution and in the presence of seed crystals. On the other hand, under glycothermal conditions, a-alumina is formed at 285°C for 4 h. The equilibrium point between diaspore (another polymorph of AlOOH) and a-alumina under the saturated vapor pressure of water was determined to be 360°C. However, near the equilibrium point, the transformation rate is very sluggish, and only a small conversion of diaspore is observed. Therefore complete conversion of diaspore into a-alumina requires a much higher temperature. Since boehmite is slightly less stable than diaspore, the hypothetical equilibrium point between boehmite and a-alumina would be lower than that for diaspore-alumina. However, a-alumina would not be formed by a hydrothermal reaction at such a low temperature as has been achieved in the glycothermal reaction. 

Correlation of the Solubility of Solids in Various SCF. The new LC mixing rules were also tested for the solubility of a large number of solid solutes in various SCFs. The critical temperatures and pressures of solids and SCFs were taken from refs 24 and 25. The molar volumes of the solids and their saturated vapor pressures were taken from ref 25. The saturated vapor pressure of perylene was found in ref 26. The results are compared with the van der Waals mixing rules in Table 2, which shows that they are comparable. The parameters of SRK EOS (a and b) can be expressed by combining one of eqs 17a—c with one of eqs 18a—c. Only a few combinations have been included in Table 2 the other ones have also been tested and provided comparable results. 

Problem 10.10 A Dumas nitrogen analysis of a 5.72-mg sample of jhphenylene-diamine gave 1.31 cc of nitrogen at 20° and 746 mm. The gas was collect over saturated aqueous KOH solution (the vapor pressure of water, 6 mm). Calculate the percentage of nitrogen in the compound. 

By comparing the weight of the aerogel at 0 and 30 % relative humidity the amount of water that each RF aerogel adsorbs is determined. After storing the samples at 90 °C for 48 h and cooling down to room temperature in dry N2-atmosphere the weight at 0 % relative humidity is measured. To obtain the values at 30 % relative humidity the samples are placed in a closed cell with a specific salt-water solution. By vapor pressure depression above saturated solutions this specific solution keeps the atmosphere constant at 30 % relative humidity. 

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