Acid water systems

Abstract. A model of the conformational transitions of the nucleic acid molecule during the water adsorption-desorption cycle is proposed. The nucleic acid-water system is considered as an open system. The model describes the transitions between three main conformations of wet nucleic acid samples A-, B- and unordered forms. The analysis of kinetic equations shows the non-trivial bifurcation behaviour of the system which leads to the multistability. This fact allows one to explain the hysteresis phenomena observed experimentally in the nucleic acid-water system. The problem of self-organization in the nucleic acid-water system is of great importance for revealing physical mechanisms of the functioning of nucleic acids and for many specific practical fields. 

Tolstorukov, M.Ye., Gatash, S.V., Maleev, V.Ya. Self-organization and non-iinear dynamics of nucleic acid-water system. Special Issue of Int. J. Bif. Chaos (in press)... 

A tabulation of the partial pressures of sulfuric acid, water, and sulfur trioxide for sulfuric acid solutions can be found in Reference 80 from data reported in Reference 81. Figure 13 is a plot of total vapor pressure for 0—100% H2SO4 vs temperature. References 81 and 82 present thermodynamic modeling studies for vapor-phase chemical equilibrium and liquid-phase enthalpy concentration behavior for the sulfuric acid—water system. Vapor pressure, enthalpy, and dew poiat data are iacluded. An excellent study of vapor—liquid equilibrium data are available (79). 

FIG. 13-68 Separation of nitric acid-water system with sulfuric acid in a two-column sequence exploiting extreme boundary curvature. 

FIG. 15-51 Effect of reciprocating speed on HETS, o-xylene-acetic acid-water system. Lo and Pmchazka in Lo et al., p. 377.)... 

The phase diagram for the dodecane 1-sulfonic acid/water system was drawn from data obtained by visual inspection, microscopic observations through a... 

About the same time Beutier and Renon (11) also proposed a similar model for the representation of the equilibria in aqueous solutions of weak electrolytes. The vapor was assumed to be an ideal gas and < >a was set equal to unity. Pitzer s method was used for the estimation of the activity coefficients, but, in contrast to Edwards et al. (j)), two ternary parameters in the activity coefficient expression were employed. These were obtained from data on the two-solute systems It was found that the equilibria in the systems NH3+ H2S+H20, NH3+C02+H20 and NH3+S02+H20 could be represented very well up to high concentrations of the ionic species. However, the model was unreliable at high concentrations of undissociated ammonia. Edwards et al. (1 2) have recently proposed a new expression for the representation of the activity coefficients in the NH3+H20 system, over the complete concentration range from pure water to pure NH3. it appears that this area will assume increasing importance and that one must be able to represent activity coefficients in the region of high concentrations of molecular species as well as in dilute solutions. Cruz and Renon (13) have proposed an expression which combines the equations for electrolytes with the non-random two-liquid (NRTL) model for non-electrolytes in order to represent the complete composition range. In a later publication, Cruz and Renon (J4J, this model was applied to the acetic acid-water system. 

The situation is quite different in the case of an acetic acid-water system. The energy of acetic acid adsorption on platinum is low and therefore the voltammetric curves taken in the absence and in the presence of acetic acid in the supporting electrolyte are nearly the same. However, radiometric data show that C-labeled acetic acid is adsorbed on the electrode surface. Most likely the acetic acid molecules are adsorbed on the top of the water molecules populating the electrode surface. Simultaneously recorded voltammetric and counting rate data are shown in Fig. 8. 

Ferris, L.M. Lead nitrate-nitric acid-water system. J. Chem. Eng. Data, 5(3) 242, 1960a. 

Jaecker-Voirol, A., and P. Mirabel, Heteroniolecular Nucleation in the Sulfuric Acid-Water System," Atmos. Environ., 23, 2053-2057 (1989). 

Wyslouzil, B. E., J. H. Seinfeld, R. C. Flagan, and K. Okuyama, Binary Nucleation in Acid-Water Systems. II. Sulfuric Acid-Water and a Comparison with Methanesulfonic Acid-Water, J. Chem. Phys., 94, 6842-6850 (1991). 

The value of / for p-nitroaniline is measurable with adequate precision in sulfuric acid-water systems up to 24% [w/w] of acid. Within this range, Hammett defined the operational measure Hq of acidity of the solution by Eq. (29). 

The fact that the difference log /b — log I p remains essentially constant within the region of measurable overlap of the two indicators means that within this region the last term in Eq. (31) is essentially independent of the medium for all these strong acid-water systems. If the constancy extends beyond the overlap region to very dilute solutions in water, and if the value of the term is assumed to be zero (assumption 1), Eq. (31) leads to... 

T. Vermeulen and co-workers, Vapor-.Eiquid Equilibrium of the Sulfuric Acid/ Water System, AIChE meeting, Anaheim, Calif., (June 10, 1982). 

As the author points out, the sulfuric acid-water system is one of the few examples of a liquid binary system in which certain properties change discontinuously. In this case dsjdp, where s is the specific gravity and p the per cent concentration of H2S04, has discontinuities at certain values of p. The most pronounced correspond to the compositions H2S04—H20 and H2S04—2H20. Mendeleev (102) believes that these characteristic points are connected with the formation in the solutions of definite chemical compounds. The more stable the compound the sharper the discontinuity in the property versus composition. 

Figure 26. Variation of the fluorescent lifetime of Tb2(S04)3 in a sulfuric acid-water system as a function of water concentration [from Ref. (/0/)J.

Table I summarizes the effect of such nitrates on the azeotropic composition in the nitric acid-water system. Addition of potassium nitrate increases the azeotropic composition, but other nitrates decrease it, the amount by which the azeotrope is displaced being proportional to the amount of nitrate added. The azeotrope is eliminated completely at salt concentrations of 45, 48, 54, or 64% by weight for addition of magnesium, zinc, lithium, or calcium nitrates respectively.

For the benzene-hydrochloric acid-water system there was no point in screening several zeolites for... 

This Hr function, also called J0 function, has also been used to measure the acidity of the sulfuric acid-water and perchloric acid-water systems. It shows a large deviation from the H0 scale in the highly concentrated solutions as shown in Figure 1.1. 

L. Lefrancois, J. J. Delpuech, M. Hebrant, J. Chrisment, and C. Tondre. Aggregation and protonation phenomena in third phase formation An NMR study of the quaternary malon-amide/dodecane/nitric acid/water system. J. Phys. Chem. B, 105(13) 2551-2564, 2001. 

The vapor-liquid equilibrium for the nitric acid / water system at atmospheric pressure is shown in Figure 9.4. This figure shows that a concentration of 68.4 weight % nitric acid is the maximum (i.e., the azeotropic point) that can be obtained by simple distillation of the weak acid220. 

Figure 9.4. Vapor-liquid equilibrium of nitric acid - water system. (Reproduced by permission of Heraeus Nitric Acid Conference, November, 2001)...

Fig. 2. Thermal analysis of nitric acid-water system.

Resin Beads. The resin beads are prepared from commercially available Dowex 50W-X8, a sulfonic acid cation exchange resin. The 8% cross-linked resin was chosen because it does not shrink or expand excessively in acid-water systems and because it is readily available. Resin cross-linkage had no detectable effect on the final oxide products in the development test runs. The resin is hydraulically classified to produce a size fraction that is predominately 60-80 m in diameter. The classified resin is washed with 6 M HC1 to remove contaminants such as iron and rinsed thoroughly with water. 

This polymer is spun from a solution in pure (100%) sulphuric acid. A typical, but too simple phase diagram for the PpPTA-sulphuric acid/water system is shown in Fig. 19.24 (also shown as Fig. 16.27). It shows that the solution is solid at sulphuric acid/water ratio smaller than approximately 0.95 liquid solutions are obtained at high sulphuric acid contents at low polymer concentrations isotropic solutions are obtained whereas at higher polymer concentrations the solutions are anisotropic. It is clear that for solution spinning almost pure sulphuric acid or even oleum (i.e. H2SO4... 

This correlation was in reasonable agreement with the low gas flow (Gg < 0.01 g cm-2 s1) data of Sato et al.74 for a benzoic acid-water system with 5.5- and 12.2-mmparticle diameter. Hirose et al.38 made extensive measurements in trickle-flow, pulsed-flowrand bubble-flow regimes and correlated the enhancement factor in Ks due to parallel gas flow with the liquid velocity. They found that this enhancement factor (ratio of Ks in the presence of gas flow to Ks in the absence of gas flow) was inversely proportional to the total liquid holdup and to a first approximation has the value 2. Their data for Ks as a function of liquid velocity... 

Karr and Lo [63] have developed sin jle scaling rules for the Karr extractor. To scale HETS from one column size to another, requires that the plate spacing, amplitude, and total volumetric flow rate per unit area be kept the same for each extractor. They foimd for a high interfacial-tension system such as the o-xylene, acetic-acid, water system, that... 

According to Heist [55], in the case of low acid concentrations in the order of 1 percent by weight, no process other than freeze crystallization is capable of economic acid recovery. For the acetic acid/water system, the process is based on the phase diagram shown in Figure 54, where the eutectic temperature is seen to be -26.7 C. 

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