Aqueous solutions vapor pressure

NaCl molecules in its aqueous solution. Vapor pressure lowering of dilute NaCl solutions obeys Raoult s law for the solvent water—that is, pw = PwXw— and the vapor pressure corresponds to fwo solute species. 

Trimellific anhydride (TMAN [CAS 552-30-7]) Dusts and vapors extremely irritating to eyes, nose, throat, skin, and respiratory tract. Potent respiratory sensitizer (asthma). Can also cause diffuse lung hemorrhage (pulmonary hemosiderosis). 0.04 mg/m (C) Colorless solid. Hydrolyzes to trimellitic acid in aqueous solutions. Vapor pressure is 0.000004 mm Hg at 25°C (77°F). TMAN is an important component of certain epoxy coatings. 

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. 

Ammonia is readily absorbed ia water to make ammonia liquor. Figure 2 summarizes the vapor—Hquid equiUbria of aqueous ammonia solutions and Figure 3 shows the solution vapor pressures. Additional thermodynamic properties may be found ia the Hterature (1,2). Considerable heat is evolved duriag the solution of ammonia ia water approximately 2180 kJ (520 kcal) of heat is evolved upon the dissolution of 1 kg of ammonia gas. 

In the second edition of this volume, special attention has been paid lo improving the accuracy of the estimation techniques used for liquid heat capacity, vapor and liquid viscosity. and vapor thermal conductivity. Improved methods of extending data on liquid density and thermal conductivity have been used m this edition New experimental data has also been included. Particular attention has been paid to include new data on aqueous solution and pressure effects on physical properties... 

Crystals can be grown from aqueous solutions under pressure. The solubility of ceramic materials in water below its boiling point is low, but it may become significant at, say, 300°C in autoclaves, where the vapor pressure exceeds 1000 atm (Fig. 1). The... 

Truhlar et al. [28] predict the aqueous solubilities of 75 liquid solutes and 15 solid solutes by utilizing a relation between solubility, free energy of solvation and solute vapor pressure. The method is based on SM5.42R solvation model and the classical thermodynamic theory of solutions. In the SM5.42R solvation model the free energy of solvation is written as, AG° = + Gp+ Gcds where AEp. is the change of electronic energy due... 

In determining the lean/rich exchanger duty, Qm, it is first necessary to determine the regenerator bottoms temperature, Tg. This temperature is fixed by the lean amine composition, the lean amine type, and the regenerator pressure profile. As previously noted, a pressure drop of about 5 psi from the reflux drum to the stripper bottoms should be allowed. Available aqueous amine solution vapor pressure data are then used to determine the stripper bottoms temperature, Tg. See Figures 2-56,2-57,2-58,2-59,2-60, and 2-61 for vapor pres-sure/temperature data for MEA, DEA, DGA, lEA, DIPA, and MDEA, respectively. 

Table 3. Vapor Pressure of Aqueous Solutions of Aeetaldehyde...

Table 5. Acrylonitrile Vapor Pressure over Aqueous Solutions at 25°C ...

Figure 2 shows the vapor pressures of anhydrous hydrazine (AH), monomethyUiydrazine [60-34-4] (MMH), and unsymmetrical dimethyUiydrazine [57-14-7] (UDMH) as a function of temperature (2). The partial pressures of N2H4 over aqueous solutions of various concentrations are plotted in Figure 3. 

Hydrogen Chloride—Water System. Hydrogen chloride is highly soluble in water and this aqueous solution does not obey Henry s law at ah concentrations. Solubhity data are summarized in Table 5. The relationship between the pressure and vapor composition of unsaturated aqueous hydrochloric acid solutions is given in Reference 12. The vapor—Hquid equiHbria for the water—hydrogen chloride system at pressures up to 1632 kPa and at temperatures ranging from —10 to +70° C are documented in Reference 13. 

The high solubility of the salt and resultant low water vapor pressure (58) of its aqueous solutions ate usehil ia absorption air conditioning (qv) systems. Lithium bromide absorption air conditioning technology efficiencies can surpass that of reciprocal technology usiag fluorochlorocarbon refrigerants. 

Lithium Iodide. Lithium iodide [10377-51 -2/, Lil, is the most difficult lithium halide to prepare and has few appHcations. Aqueous solutions of the salt can be prepared by carehil neutralization of hydroiodic acid with lithium carbonate or lithium hydroxide. Concentration of the aqueous solution leads successively to the trihydrate [7790-22-9] dihydrate [17023-25-5] and monohydrate [17023-24 ] which melt congmendy at 75, 79, and 130°C, respectively. The anhydrous salt can be obtained by carehil removal of water under vacuum, but because of the strong tendency to oxidize and eliminate iodine which occurs on heating the salt ia air, it is often prepared from reactions of lithium metal or lithium hydride with iodine ia organic solvents. The salt is extremely soluble ia water (62.6 wt % at 25°C) (59) and the solutions have extremely low vapor pressures (60). Lithium iodide is used as an electrolyte ia selected lithium battery appHcations, where it is formed in situ from reaction of lithium metal with iodine. It can also be a component of low melting molten salts and as a catalyst ia aldol condensations. 

Extensive hydrogen bonding takes place in phosphoric acid solutions. In concentrated (86% H PO solutions, as well as in the crystal stmctures of the anhydrous acid and the hemihydrate, the tetrahedral H PO groups are linked by hydrogen bonding. At lower (75% H PO concentrations, the tetrahedra are hydrogen-bonded to the water lattice. Physical properties of phosphoric acid solutions of various concentrations are Hsted in Table 2 the vapor pressure of aqueous H PO solutions at various temperatures is given in Table 3. 

The methylamiaes and ethylamiae have vapor pressures above atmospheric at ambient temperatures and are available ia the pure form only ia pressurized containers. These amines are also sold as aqueous solutions with vapor pressures below atmospheric for ease of handling. Diethylamiae, triethylamiae, and all of the higher mol wt amines are sold as the pure compounds. 

Fig. 3. Vapor pressure of aqueous ammonia solution (1). Numbers represent the weight percent of ammonia in the Hquid. To convert kPa to psi, multiply...

Physical and Chemical Properties. Ammonium nitrate is a white, crystalline salt, df = 1.725, that is highly soluble in water, as shown in Table 3 (7). Although it is very hygroscopic, it does not form hydrates. This hygroscopic nature compHcates its usage in explosives, and until about 1940, was a serious impediment to its extensive use in fertilizers. The soHd salt picks up water from air when the vapor pressure of water exceeds the vapor pressure of a saturated aqueous ammonium nitrate solution (see Table 4). 

BeryUium chloride [7787-47-5], BeCl2, is prepared by heating a mixture of beryUium oxide and carbon in chloride at 600—800°C. At pressures of 2.7—6.7 Pa (0.02—0.05 mm Hg) beryllium chloride sublimes at 350—380°C. It is easily hydrolyzed by water vapor or in aqueous solutions. BeryUium chloride hydrate [14871-75-1] has been obtained by concentrating a saturated aqueous solution of the chloride in a stream of hydrogen chloride. ChloroberyUate compounds have not been isolated from aqueous solutions, but they have been isolated from anhydrous fused salt mixtures. 

Forms of Boric Acid. Orthoboric acid, B(OH)3, formula wt, 61.83, crystaUi2es from aqueous solutions as white, waxy plates that are triclinic ia nature sp gi 4, 1.5172. Its normal melting poiat is 170.9°C, however, when heated slowly it loses water to form metaboric acid, HBO2, formula wt, 43.82, which may exist ia one of three crystal modifications. Orthorhombic HBO2-III or a-form d = 1.784 g/mL, mp = 176° C) forms first around 130°C and gradually changes to monoclinic HBO2-II or P-form (d = 2.045 g/mL, mp = 200.9° C). Water-vapor pressures associated with these decompositions foUow. To convert kPa to mm Hg, multiply by 7.5. 

The pH of a borax solution iacreases slightly with increasing concentration (Table 10) and drops slightly with increasing temperature. The vapor pressures of aqueous saturated borax solutions at various temperatures are (73,74) ... 

Hypochlorous acid and chlorine monoxide coexist in the vapor phase (78—81). Vapor pressure measurements of aqueous HOCl solutions show that HOCl is the main chlorine species in the vapor phase over <1% solutions (82), whereas at higher concentrations, CI2O becomes dominant (83). The equihbtium constant at 25°C for the gas-phase reaction, determined by ir and uv spectrophotometry and mass spectrometry, is ca 0.08 (9,66,67,69). The forward reaction is much slower than the reverse reaction. 

Total Vapor Pressures of Aqueous Solutions of CH3COOH, , 2-85... 

Vapor Pressure of Aqueous Diethylene Glycol Solutions... 

FIG. 2-3 Vapor pressure of aqueous diethylene glycol solutions. Coutiesy of Cafhide and Carhon Chemicals Coip.)... 

FIG. 2-29 Enthalpy-concentration diagram for aqueous sodium hydroxide at 1 atm. Reference states enthalpy of liquid water at 32 F and vapor pressure is zero partial molal enthalpy of infinitely dilute NaOH solution at 64 F and 1 atm is zero. [McCahe, Trans. Am. Inst. Chem. Eng., 31, 129(1935).]... 

The vapor pressure is reduced. This has a significant effect on the rate of release of material boiling at less than ambient temperature. It may be possible to store an aqueous solution at atmospheric pressure, such as aqueous ammonium hydroxide instead of anhydrous ammonia. 

TABLE 26-9 Vapor Pressure of Aqueous Ammonio/ Hydrochloric Acid, and Monomethylamine Solutions... 

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