Nitric acid hydrate

An interesting inorganic example is that of nitric acid hydrate. In the liquid... 

Iraci, L. T., A. M. Middlebrook, M. A. Wilson, and M. A. Tolbert, "Growth of Nitric Acid Hydrates on Thin Sulfuric Acid Films, Geophys. Res. Lett., 21, 867-870 (1994). 

According to Sapozhnikov, the esterification proceeds most intensively in the presence of anhydrous nitric add HN03, as in eqn. (2). In the presence of smaller amounts of sulphuric acid, nitric acid hydrates are formed in practice they are not capable of esterifying cellulose. 

Nitric acid hydrate exists in balance with its components. Therefore there is a further equilibrium value ... 

The considerable heat evolved on dilution of nitric acid with water proves that the nitric acid hydrates are stable. With an excess of nitric acid the heat amounts to 3.5 kcal per mole of water. It has been suggested that the nitric acid hydrate, HN03.H20, present in concentrated nitric acid is undissociated and that the water molecules are attached to the nitric acid molecules by hydrogen bonds. Thus there would be the equilibrium ... 

On adding water the intensity of the band 3400 cm 1 decreases while that of the other bands increases. It seems very likely that the bands at -3400 cm 1 belong to nitric acid molecules linked by hydrogen bond (pp. 7-8), while the lines at 2550, 2700 and 3150 cm 1 probably belong to nitric acid hydrate molecules. 

Although Rowland and Molina had predicted depletion of ozone concentrations by these reactions, there were many who doubted their conclusions. The phenomenon that finally brought the problem to the attention of the world was the discovery of the ozone hole over the Antarctic in 1985. During the winter, a combination of air flow pattern and low temperature create stratospheric clouds of ice particles. The surface of these particles is an ideal location for reaction of NO2, OCl, and O3. These clouds contain nitric acid hydrate, formed by... 

There is IR and Raman evidence for a phase transition for nitric acid hydrate, near 200 K.536 RAIR and ab initio calculations gave information on the structure and vibrational wavenumbers for crystalline nitric acid.537 A DRIFTS study has been performed on the interaction of gas-phase IIN03 with ice and acid (HC1, HN03) hydrate surfaces.538 An ab initio calculation of the vibrational wavenumbers of nitric acid hydrates, HN03.(Fl20)n, where n = 1, 2 or 3, has been reported.539... 

Toon, O.B., M.A. Tolbert, B.G. Koehler, A.M. Middlebrook and J. Jordan Infrared optical constants of H2O ice, amorphous nitric acid solutions, and nitric acid hydrates, J. Geophys. Res. (Atmos.) 99 (1994) 25631-... 

The explanation for this unexpectedly sharp decrease in ozone lies in a particular phenomenon of the Antarctic winter it is cold enough in winter in the stratosphere over Antarctica to form polar stratospheric clouds (PSCs) of nitric acid hydrate, HNO3 XH2O, where x 3. The normal end fate of chlorine atoms in the stratosphere is to be incorporated in hydrochloric acid, HCl, which does... 

Tizek et al., 2004] H. Tizek, E. Knozinger, and H. Grothe. Formation and phase distribution of nitric acid hydrates in the mole faction range a (HN03) < 0.25 A combined XRD and IR study. Physical Chemistry and Chemical Physics 6 972-979, 2004. 

Figure 4 shows the stratospheric particle zoo with all currently known or speculated transitions between diflTerent particles . Phases shown are either marked as liquid (1) or as a sulfuric acid hydrate (SAX, with X = M, T, H, etc., including the mixed hydrate MIX) or nitric acid hydrate (NAX, with X = T, D, P etc.). On the left hand side the diagram shows the stability regions of the solid phases under typical stratospheric conditions at 50 mbar (5 ppmv H2O, 10 ppbv HNO3). The right hand side of Fig. 4 shows transitions relating these phases. Thermodynamically allowed transitions that are also kinetically feasible are marked by an arrow (-+), while transitions which are thermodynamically allowed but kinetically so slow that they will not occur in the stratosphere are marked by crossed arrows ). 

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