The nitrate ion

Pi bond delocalization furnishes a means of expressing the structures of other molecules that require more than one electron-dot or structural formula for their accurate 

Left the unhybridized 2p atomic orbitals of the carbon atoms are shown superimposed on the trigonally-hybridized sp2 sigma bonding system. Right overlap ofthe sp2 orbitals leads to a pi orbital system that extends around the molecule 

Nitrogen has three half-occupied p orbitals available for bonding, all perpendicular to one another. Since the nitrate ion is known to be planar, we are forced to assume that the nitrogen outer electrons are sp2 hybridized. The addition of an extra electron fills all three hybrid orbitals completely. Each of these filled sp2 orbitals forms a a bond by overlap with an empty oxygen 2pz orbital this, you will recall, is an example of coordinate covalent bonding, in which one of the atoms contributes both of the bonding electrons. 

The empty oxygen 2p orbital is made available when the oxygen electrons themselves become sp hybridized we get three filled sp hybrid orbitals, and an empty 2p atomic orbital, just as in the case of nitrogen. 

The % bonding system arises from the interaction of one of the occupied oxygen sp orbitals with the unoccupied 2pz orbital of the nitrogen. Notice that this, again, is a coordinate covalent sharing, except that in this instance, it is the oxygen atom that 

---

Strong oxidising agents such as acidified potassium manganate(VII) oxidise NOj to the nitrate ion ... 

Tin(ll) chloride, in presence of hydrochloric acid, is oxidised to tin(IV) chloride, the nitrate ion in this case being reduced to hydroxylamine and ammonia. 

The infra-red absorption bands of molecular nitric acid do not change as the medium is varied beween 100% and 70% of acid on further dilution the nitrate ion becomes the dominant species. ... 

The two absorption bands, at 1050 and 1400 cm , which appear in the Raman spectra of solutions of nitric acid in concentrated sulphuric acid are not attributable to either of the acid molecules. In oleum the lower band appears at 1075-1095 cm. That these bands seemed to correspond to those in the spectra of anhydrous nitric acid and solid dinitrogen pentoxide caused some confusion in the assignment of the spectrum. The situation was resolved by examining the Raman spectra of solutions of nitric acid in perchloric or selenic acids , in which the strong absorption at 1400 cm is not accompanied by absorption at about 1050 cm . Thus, the band at 1400 cm arises from the nitronium ion, and the band at about 1050 cm can be attributed in the cases of nitric acid and solid dinitrogen pentoxide to the nitrate ion formed according to the following schemes ... 

Bismuth subnitrate [1304-85-4] (basic bismuth nitrate) can be prepared by the partial hydrolysis of the normal nitrate with boiling water. It has been used as an antacid and in combination with iodoform as a wound dressing (183). Taken internally, the subnitrate may cause fatal nitrite poisoning because of the reduction of the nitrate ion by intestinal bacteria. 

In contrast to the stepwise oxidation of sodium hyponitrite in liquid N2O4, the oxidation goes rapidly to the nitrate ion in an inert solvent of high dielectric constant such as nitromethane ... 

Similar considerations apply to oxidation. An anion which is considerably more stable than water will be unaffected in the neighbourhood of the anode. With a soluble anode, in principle, an anion only needs be more stable than the dissolution potential of the anode metal, but with an insoluble anode it must be stable at the potential for water oxidation (equation 12.4 or 12.5) plus any margin of polarisation. The metal salts, other than those of the metal being deposited, used for electroplating are chosen to combine solubility, cheapness and stability to anode oxidation and cathode reduction. The anions most widely used are SOj", Cl", F and complex fluorides BF4, SiFj , Br , CN and complex cyanides. The nitrate ion is usually avoided because it is too easily reduced at the cathode. Sulphite,... 

Another species for which it is necessary to invoke the idea of resonance is the nitrate ion. Here three equivalent structures can be written... 

Resonance can be anticipated when it is possible to write two or more Lewis structures that are about equally plausible. In the case of the nitrate ion, the three structures we have written are equivalent. One could, in principle, write many other structures, but none of them would put eight electrons around each atom. 

The nitrate ion of the nitric acid acts as the oxidizing agent. The function of the hydrochloric add is to furnish Cl ions to form the very stable complex ion Audi. ... 

Concentrated (16 M) nitric acid is a strong oxidizing agent the nitrate ion is reduced to nitrogen dioxide. This happens when 16 M HN03 reacts with copper metal (Figure 21.9) ... 

This principle can be applied to species such as the nitrate ion, whose Lewis structure is ... 

Valence bond theory (Chapter 7) explains the fact that the three N—O bonds are identical by invoking the idea of resonance, with three contributing structures. MO theory, on the other hand, considers that the skeleton of the nitrate ion is established by the three sigma bonds while the electron pair in the pi orbital is delocalized, shared by all of the atoms in the molecule. According to MO theory, a similar interpretation applies with all of the resonance hybrids described in Chapter 7, including SO S03, and C032-. 

Theory. The anion exchange resin, originally in the chloride form, is converted into the nitrate form by washing with sodium nitrate solution. A concentrated solution of the chloride and bromide mixture is introduced at the top of the column. The halide ions exchange rapidly with the nitrate ions in the resin, forming a band at the top of the column. Chloride ion is more rapidly eluted from this band than bromide ion by sodium nitrate solution, so that a separation is possible. The progress of elution of the halides is followed by titrating fractions of the effluents with standard silver nitrate solution. 

Solutions of cerium(IV) sulphate may be prepared by dissolving cerium(IV) sulphate or the more soluble ammonium cerium(IV) sulphate in dilute (0.5-1.0M) sulphuric add. Ammonium cerium(IV) nitrate may be purchased of analytical grade, and a solution of this in 1M sulphuric add may be used for many of the purposes for which cerium(IV) solutions are employed, but in some cases the presence of nitrate ion is undesirable. The nitrate ion may be removed by evaporating the solid reagent which concentrated sulphuric add, or alternatively a solution of the nitrate may be predpitated with aqueous ammonia and the resulting cerium(IV) hydroxide filtered off and dissolved in sulphuric acid. 

The nitrate ion is reduced to ammonium ion at a lower (i.e. less negative) cathode potential than that at which hydrogen ion is discharged, and, therefore, acts to decrease hydrogen evolution. The nitrate ion acts as a cathodic depolariser. 

The reduction potential of the nitrate ion is lower than the discharge potential of hydrogen, and therefore hydrogen is not liberated. The nitric acid must be free from nitrous acid, as the nitrite ion hinders complete deposition and introduces other complications. The nitrous acid may be removed (a) by boiling the nitric acid before adding it, (b) by the addition of urea to the solution ... 

Two platinum electrodes are immersed in sulphuric acid of suitable concentration containing the nitrate ion to be determined and a potential of about 100 millivolts is applied. Upon titration with 0.4M ammonium iron(II) sulphate solution there is an initial rise in current followed by a gradual fall, with a marked increase at the end point the latter is easily determined from a plot of current against volume of iron solution added. The concentration of water should not be allowed to rise above 25 per cent (w/w). The temperature of the solution should not exceed 40 °C. 

The nitrate ion (N03) is one of the most electronegative ions and its absolute velocity... 

Because all three bonds are identical, a better model of the nitrate ion is a blend of all three Lewis structures with each bond intermediate in properties between a single and a double bond. This blending of structures, which is called resonance, is depicted in (9) by double-headed arrows. The blended structure is a resonance hybrid of the contributing Lewis structures. A molecule does not flicker between different structures a resonance hybrid is a blend of structures, just as a mule is a blend of a horse and a donkey, not a creature that flickers between the two. 

Sodium nitrate, NaNOs, is an example of an ionic substance that contains a group of atoms with a net charge. Sodium is present as Na atomic cations. The other atoms of sodium nitrate are grouped together in one structure, NO3, which carries a -1 charge (Figure S-lOl. This anion is a molecular ion, the nitrate ion. The... 

The kinetics are the same in sulphuric and phosphoric acid media as in perchloric acid. The main kinetic features are reproduced in a nitric acid medium although a term, k[Ag(II)]V[Ag(I)], is also involved. Both terms include a strong inverse acidity dependence however, the role of the nitrate ions obscures this. 

---