Nitric acid, anhydrous structure

The chemical properties of nitric acid require us to consider the structure first. The vapour of pure nitric acid (i.e. anhydrous) is probably composed of molecules of hydrogen nitrate , which structurally is a resonance hybrid of such forms as ... 

Related studies have been made using perchloric acid. From mixtures of anhydrous nitric and perchloric acids in the appropriate proportions, Hantzsch " claimed to have isolated two salts whose structures supported his hypothesis concerning the nature of nitric acid in strong mineral acids. He represented the formation of the salts by the following... 

PF6, SbF6, C104-, FSO3 counterions. The X-ray crystal structure of nitronium ion is known with hydrosulfate anion.515 The most widely used tetrafluoroborate nitronium salt (N02+BF4 ) is prepared by treating a mixture of nitric acid and anhydrous hydrogen fluoride wit boron trifluoride516 [Eq. (4.145)]. 

In the days when anhydrous nitric acid was not easily available, nitric acid salts (NaN03, KN03) mixed with sulphuric acid were widely used for nitration. Such mixtures acted similarly to the mixture of nitric and sulphuric acids. Later, as synthetic nitric acid became one of the most readily available chemical products, and the production of nitric acid salts from nitric acid had started, nitrating mixtures with sodium or potassium nitrates were abandoned. This is the principal explanation for the scarcity of investigations on the structure and action of such mixtures. It is believed that in such mixtures the nitronium ions are present, according to the equation ... 

The structure of anhydrous nitric acid is interesting since the three NO bonds are not identical and the experimental evidence suggests that the molecule consists of an hydroxyl group and a nitro group. There are two NO bond lengths of i 21 A, and one of i 4 A, thus corresponding to the formula... 

Anhydrous Th(N03)4 is obtained by heating more complex nitrates under vacuum. Hexani-trato complexes are obtained from moderately concentrated (8M to 14 M) nitric acid, in the presence of sulfamic acid to inhibit oxidation by nitrite in the case of uranium(I V). The nitrate groups in these compounds are bidentate and the structure of the anion is distorted icosahedral. 

Covalent nitrates. Apart from organic nitrates covalent nitrates of non-metals are limited to those of H, F, and Cl. (CINO3 has been prepared from anhydrous HNO3 and CIF as a liquid stable at —40°C in glass or stainless steel vessels. 9 Electron diffraction studies have been made of the explosive gas FN03 and of the (planar) methyl nitrate molecule. A refinement of the crystal structure of pentaerythritol nitrate, C(CH20N02)4, shows that the nitrate group has the same structure, (d), as in nitric acid. 

For the preparation of washcoated monoliths the suspensions of sol-aluminium hydroxide with pseudoboehmite structure have been used. This sol formed during the reaction between the hydroxide and nitric acid serves both as a binder and a source of y-A Oa in the final product after calcination. Salts of additives were introduced into sol. The influence of the following parameters on the formation of thermostable washcoated layer have been studied concentration of anhydrous alumina in the sol amount of added HNO3 dipping time number of dippings drying and calcination duration. 

C. Nital is perhaps the most common etchant and stain for silicates and improves with age. Nital is 1.5 mL of nitric acid (HNO ) in 100 mL of ethyl, methyl, isopropyl, or amyl alcohol. The author routinely uses asolution of 1 mL of HNOj and 99 mL of anhydrous isopropyl alcohol. The solution quickly reacts in 6 to 10 seconds with alite and belite. At a 0.05% dilution the reaction time is 20 to 40 seconds. Ono (1995) relates alite reactivity to color produced with 0.2% nital. Depending on the relative reactivity of silicates, alite normally turns blue to green, belite is brown to blue—both silicates showing details of internal structure. Nital superimposed on a 20-second potassium hydroxide etch turns C3A light brown and colors the silicates. 

The anhydrous acid can be produced by distillation, and is a colourless pungent liquid. The nitric acid molecule is planar, as shown in Structure 11.9. 

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