NaCl vapor pressure

A saturated aqueous solution in contact with an excess of a definite solid phase at a given temperature will maintain constant humidity in an enclosed space. Table 11.4 gives a number of salts suitable for this purpose. The aqueous tension (vapor pressure, in millimeters of Hg) of a solution at a given temperature is found by multiplying the decimal fraction of the humidity by the aqueous tension at 100 percent humidity for the specific temperature. For example, the aqueous tension of a saturated solution of NaCl at 20°C is 0.757 X 17.54 = 13.28 mmHg and at 80°C it is 0.764 X 355.1 = 271.3 mmHg. 

Figure 16. Vapor pressure versus temperature of a NaCl-A1C1, mixture with 49.5 mol% A1C13.

C to about 130 mmHg at 800 °C. Over mixtures which are NaCl-rich (i.e., AlCl, 25mol%, NaCl 75 mol%) the partial pressure of A1C13 becomes significantly less than for the pure tetrachloroaluminate. The vapor pressure of A1C13 amounts at 790 °C to 14.9 mm Hg and that of NaAlCI4 to 56.6 mm Hg. 

In the discharged state of ZEBRA batteries NaCl is formed in the positive electrode, which is beside the NaAlCl4. In abuse experiments, e.g., overheating, less volatile material will be released in the discharged state compared with the charged state where no NaCl is present. This is due to the lower vapor pressure of mixtures with increased NaCl content. 

Fig. 4. Vapor pressure of the AlCl3-NaCl molten salt as a function of the AICI3 mole fraction and the temperature. The data used to construct this plot were taken from Viola et al. [41]...

The approximate relative humidity then will be 90% (90.04 %), because the water vapor pressure above the NaCl saturated solution will be 90.04% of the vapor pressure of pure water at 20° C. 

To prove that this method can be applied also to solids with strong ionic bonding, NaCl was investigated as an example. Also in this case an aluminia Knudsen cell was used, the orifice diameter was calibrated with gold. Figure 69 shows a graphical presentation of the vapor pressure data obtained, compared with data from the literature (Kelly)68. ... 

S02 vapor pressure (pgn2) was measured by dynamic saturation and by a gas-sensing S02 electrode over solutions containing 0.5 to 2.0 M sodium citrate at pH 3.5 to 5 with up to 1 M NaHSOj, Na2S04, and NaCl. Pgo2 was measured at 25° to 168°C pH at 25° to 95°C. Both pH and the vapor pressure ratio Ps02/pH20 were independent of temperature. The composition and temperature dependence of the data are correlated by the semiempirical expressions ... 

It is shown that the properties of fully ionized aqueous electrolyte systems can be represented by relatively simple equations over wide ranges of composition. There are only a few systems for which data are available over the full range to fused salt. A simple equation commonly used for nonelectrolytes fits the measured vapor pressure of water reasonably well and further refinements are clearly possible. Over the somewhat more limited composition range up to saturation of typical salts such as NaCl, the equations representing thermodynamic properties with a Debye-Hiickel term plus second and third virial coefficients are very successful and these coefficients are known for nearly 300 electrolytes at room temperature. These same equations effectively predict the properties of mixed electrolytes. A stringent test is offered by the calculation of the solubility relationships of the system Na-K-Mg-Ca-Cl-SO - O and the calculated results of Harvie and Weare show excellent agreement with experiment. 

This model has been applied by Vera and Vega (1 7) to the NaCl-HCl-H20 system. Table 2 presents their fit to the vapor pressures of water and the activity coefficients in the NaCl-H20 system. As can be seen in Table 2, the agreement between the model and the experimental data is very good down to 0.2 molality. In a similar way, it was also found possible to obtain an excellent fit to the experimental data for the HC1-H20 system. 

The pressure-temperature-composition diagram presented by Morey is shown in Fig. 8. The vapor pressure of pure water (on the P-T projection) terminates at the critical point (647 K, 220 bar). The continuous curve represents saturated solutions of NaCl in water, i.e., there is a three-phase equilibrium of gas-solution-solid NaCl. The gas-phase pressure maximizes over 400 bar at around 950 K. Olander and Liander s data for a 25 wt. % NaCl solution are shown, and T-X and P X projections given. At the pressure maximum, the solution phase contains almost 80% NaCl. 

From the vapor pressure data in the International Critical Tables [20], calculate the activity of the water in 1.0-, 2.0-, 2.8-, and 4.0-molal NaCl solutions at 25°C. 

Take as an example, a small dry particle of NaCl of a given mass (mu) that is introduced into air at a water vapor pressure corresponding to SA in Fig. 14.38a. Assuming that the RH is above the deliquescence point of NaCl, 75% at 25°C, the particle will take up water, dissolve, and form a stable droplet of radius rA. Similarly, if the air saturation ratio increases to Su, the particle will, under equilibrium conditions, take up water and grow to radius ru. 

If soluble anhydrite is desired, firing is maintained until a second boil occurs accompanied by a second temperature plateau at about 190°C. Virtually all the water of crystallization has been removed at 215°C. Soluble salts are impurities that increase the vapor pressure within the kettle. Aridized stucco refers to ketde-calcined hemihydrate that has been made with the intentional addition of 0.55—1.1 kilograms of NaCl or CaCl per metric ton of land plaster. The stucco characteristic of lower water demand permits higher density and higher strength casts. The hygroscopic nature of the chlorides prevents the use of aridized stucco for some applications. 

The equilibrium constants for these reactions are 8.9 x 10 8 (Eq. 17.11), 1 x 10-7 (Eq. 17.12), and 1 x 10"14 (Eq. 17.13) at 175°C [29]. As a consequence of Equation 17.13, there is a significant vapor pressure of A12C16 over acidic AlCl3-NaCl melt, making experimentation with this ionic solvent difficult. This is not a problem for the equimolar and NaCl(satd) melts. 

FIGURE 8.30 The vapor pressure of a solvent is lowered by a nonvolatile solute. The barometer tube on the left has a small volume of pure water floating on the mercury. That on the right has a small volume of 10 m NaCl(aq), and a lower vapor pressure. Note that the column on the right is depressed less by the vapor in the space above the mercury than the one on the left, showing that the vapor pressure is lower when the solute is present. 

Water temperatures in the Gulf of Mexico can be as high as 30°C along the coast during the summer. Use Table 8.3 to estimate the vapor pressure of seawater at that temperature and at 100°C and 0°C, assuming that a 0.50 m NaCl(aq) solution simulates seawater. 

Critical Tables (7) give values of vapor pressure of 5.0 and 7.5% NaCl solutions over the range of 0° to 110° C. From these data the BPE for a 7.0% solution (50% recovery) at 1 atm. is readily calculated to be 2.34° F. From the ideal solution law (which should apply well to water in dilute solutions) and the Clausius-Clapeyron equation we get... 

If an ionic substance such as NaCl is the solute, we have to calculate mole fractions based on the total concentration of solute particles (ions) rather than NaCl formula units. A solution of 1.00 mol NaCl in 15.0 mol water at 25°C, for example, contains 2.00 mol of dissolved particles (assuming complete dissociation), resulting in a mole fraction for water of 0.882 and a solution vapor pressure of 21.0 mm Hg. 

Note that because the mole fraction of water is smaller in the NaCl solution than in the glucose solution, the vapor pressure of the NaCl solution is lower 21.0 mm Hg for NaCl versus 22.3 mm Hg for glucose at 25°C. 

To take a solution of NaCl as an example, the experimentally determined van t Hoff factor for 0.05 m NaCl is 1.9, meaning that each mole of NaCl gives only 1.9 mol of particles rather than the 2.0 mol expected for complete dissociation. Of the 1.9 mol of particles, 0.1 mol is undissociated NaCl, 0.9 mol is Cl-, and 0.9 mol is Na+. Thus, NaCl is only (0.9/1.0) X 100% = 90% dissociated, and the amount of vapor pressure lowering is less than expected. 

The boiling-point elevation of a solution relative to that of a pure solvent depends on the concentration of dissolved particles, just as vapor-pressure lowering does. Thus, a 1.00 m solution of glucose in water boils at 100.51°C at 1 atm pressure (0.51°C above normal), but a 1.00 m solution of NaCl in water boils at... 

The chemical potentials measured so far do not allow the formulation of thermodynamic criteria for the formation of lyotropic mesophases. Some qualitative remarks, however, can be made. Of particular interest are Ekwall s studies of the relations between the water binding of the mesophases, their ionization, x-ray parameters, and vapor pressures (4). For common soaps at room temperature mesophases can be observed only in the presence of amounts of water that hydrate the ionic and polar groups. Hydration is therefore characteristic of aqueous lyotropic mesophases as well as micellar systems (1, 2, 3). The binding of counterions to the micelles and to the mesoaggregates seems to be of a similar electrostatic nature. The addition of NaCl greatly affects the lamellar phase D and, to a lesser extent, phase E in these phases the counterions are more strongly bound than by micelles in the solution... 

NaCl (g). Vapor pressure data were given by Fiock and Rodebush,1 Hackspill and Grandadam,1 Horiba and Baba,1 von Wartenberg and... 

Cl, and H20 in the system. However, charge neutrality requires that [Na+] = [Cl-], which reduced to 2, giving the same result in this example. If more NaCl is added to the system than will dissolve, a third phase, solid NaCl, appears. The system then has a single degree of freedom, and fixing the temperature determines the concentration of the solution and the vapor pressure of water above the solution. 

Figure 5 The relationship between vapor pressure and temperature for the Na2C03-H20 and NaCl-H20 systems.

Infrared spectra were recorded in carbon tetrachloride in 5 mm KBr liquid cells or as a thin film between NaCl plates on a Beckman IR-20 infrared spectrometer. The number-average molecular weights were determined by vapor pressure osmometry in methylene chloride solutions (3-8 g/1) (23). 

The vapor pressure of molten A1C13 is more than one atmosphere, but by addition of NaCl it decreases strongly [388,389]. This fact suggests the formation... 

A solution of sodium chloride in water has a vapor pressure of 19.6 torr at 25°C. What is the mole fraction of NaCl in this solution What would be the vapor pressure of this solution at 45°C The vapor pressure of pure water is 23.8 torr at 25°C and 71.9 torr at 45°C. 

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