The Ammonium Ion

Eighteen different ammonium salts were examined by Miller and Wilkins [6]. Two characteristic absorptions are shown, in all cases. One of these corresponds to the NH stretching vibration and occurs in the 3200 cm region, whilst there is a second absorption, also strong, in the range 1430—1390 cm .  

The lower frequency absorption near 1410 cm is reasonably strong and the band is sharp and clear-cut so that, coupled with the stretching absorption, the identification of this ion is usually relatively simple. 

Inorganic cyanides have been studied both as simple salts and as coordination complexes. Rao et al. [55] have listed data on the former, as have El Sayed and Sheline [56], and Nakamoto has given a table of a very large number of frequencies for coordination compounds [46]. The frequencies depend upon the electronegativity, oxidation number and coordination number of the atom to which the C=N group is attached [56]. In salts such as sodium 

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Acids can also exist in non-aqueous solvents. Since ammonia can also solvate a proton to give the ammonium ion. substances... 

Co-ordinate bonds are formed by the sharing of electrons, both electrons being donated by the same atom. Thus the hydrogen ion, has no outer electrons whilst ammonia has eight, six shared with hydrogen atoms and one lone-pair. This lone-pair is donated to the hydrogen ion and the ammonium ion is formed ... 

When the ammonium ion NH is formed the lone pair becomes a bonding pair and the shape becomes a regular tetrahedron. 

Reduction of dinitrogen oxide to ammonia (which gives the ammonium ion with the acid) ... 

Proton transfers convert the ammonium ion and ethoxide ion to their stable forms under the reaction conditions... 

Conservation of mass also can, with care, be applied to groups of atoms. For example, the ammonium ion, NH4, can be precipitated as Fe(NH4)2(S04)2 6H2O. Selecting NH4 as the reaction unit gives... 

When an acid and a base react, the products are a new acid and base. For example, the acetate ion, C1T3COO-, in reaction 6.7 is a base that reacts with the acidic ammonium ion, N1T45", to produce acetic acid and ammonia. We call the acetate ion the conjugate base of acetic acid, and the ammonium ion is the conjugate acid of ammonia. 

Note that the concentration of H2O is omitted from the expression because its value is so large that it is unaffected by the dissociation reaction.The magnitude of provides information about the relative strength of a weak acid, with a smaller corresponding to a weaker acid. The ammonium ion, for example, with a Ka of 5.70 X 10 °, is a weaker acid than acetic acid. 

In commercial manufactuie of ammonium peichloiate, sodium peichloiate can be the starting material. The ammonium ion can be contributed by such materials as ammonium chloride, sulfate, and nitrate, eg, the metathetical reaction of sodium perchlorate and ammonium chloride ... 

In addition to cost, several factors influence the choice of salt for a particular appHcation. The ammonium salt is the most soluble in water, but for some apphcations the presence of the ammonium ion maybe undesirable. The sodium salt is almost as soluble as the ammonium salt at ambient temperatures and above. The potassium salt is much less soluble. 

There are a considerable number of stable crystalline salts of the ammonium ion [14798-03-9] NH. Several are of commercial importance because of large scale consumption in fertiliser and industrial markets. The ammonium ion is about the same size as the potassium and mbidium ions, so these salts are often isomorphous and have similar solubiUty in water. Compounds in which the ammonium ion is combined with a large, uninegative anion are usually the most stable. Ammonium salts containing a small, highly charged anion generally dissociate easily into ammonia (qv) and the free acid (1). At about 300°C most simple ammonium salts volatilize with dissociation, for example... 

Exceptions are salts of oxidizing anions, which decompose with oxidation of the ammonium ion to nitrous oxide [10024-97-2], N2O, or nitrogen, N2. 

Ammonium nitrate fertilizer incorporates nitrogen in both of the forms taken up by crops ammonia and nitrate ion. Fertilizers (qv) containing only ammoniacal nitrogen are often less effective, as many important crops tend to take up nitrogen mainly in the nitrate form and the ammonium ions must be transformed into nitrate by soil organisms before the nitrogen is readily available. This transformation is slow in cool, temperate zone soils. Thus, ammonium nitrate is a preferred source of fertilizer nitrogen in some countries. 

For brasses, the ammonium ion is the principal cause of SCC. Few service failures have been reported when ammonia is not present. 

When organics containing reduced nitrogen are degraded, they usually produce ammonium, which is in equilibrium with ammonia. As the pK for NH3 NH4" is 9.3, the ammonium ion is the primary form present in virtually all biological treatment systems, as they operate at pH < 8.5 and usually in the pH range of 6.5-7.5. In aerobic reactions, ammonium is oxidized by nitrifying bacteria (nitrosomonas) to nitrite... 

Inhibitors as well as substrates bind in this crevice between the domains. From the numerous studies of different inhibitors bound to serine pro-teinases we have chosen as an illustration the binding of a small peptide inhibitor, Ac-Pro-Ala-Pro-Tyr-COOH to a bacterial chymotrypsin (Figure 11.9). The enzyme-peptide complex was formed by adding a large excess of the substrate Ac-Pro-Ala-Pro-Tyr-CO-NHz to crystals of the enzyme. The enzyme molecules within the crystals catalyze cleavage of the terminal amide group to produce the products Ac-Pro-Ala-Pro-Tyr-COOH and NHs. The ammonium ions diffuse away, but the peptide product remains bound as an inhibitor to the active site of the enzyme. 

The model dealt with here is greatly oversimplified, and is only of qualitative value. It treats solvation on the ammonium ions in terms of a single layer (or shell) of solvent, and ignores solvation of neutral ammonia and trimethylamine. 

Nitrogen compounds These also arise from both natural and synthetic sources. Thus ammonia is formed in the atmosphere during electrical storms, but increases in the ammonium ion concentration in rainfall over Europe in recent years are attributed to increased use of artiflcial fertilisers. Ammonium compounds in solution may increase the wettability of a metaland the action of ammonia and its compounds in causing season cracking , a type of stress-corrosion cracking of cold-worked brass, is well documented. 

Note. All values are with reference to the molarity scale. Data for bases are expressed as acidic ionisation constants e.g. for ammonia we quote pK at =9 245 for the ammonium ion... 

In Table 11 data were given ou the proton transfer from the ammonium ion to a water molecule... 

These equations say that the Kh of an amine multiplied by the of the corresponding ammonium ion is equal to Kw, the ion-product constant for water (1.00 x 10 14). Thus, if we know Ka for an ammonium ion, we also know for the corresponding amine base because /stronger base has an ammonium ion with a larger p... 

It s often possible to lake advantage of their basicity to purify amines. For example, if a mixture of a basic amine and a neutral compound such as a ketone or alcohol is dissolved in an organic solvent and aqueous acid is added, the basic amine dissolves in the water layer as its protonated salt, while the neutral compound remains in the organic solvent layer. Separation of the water layer and neutralization of the ammonium ion by addition of NaOH then provides the pure amine (Figure 24.2). 

What about amine bases In what form do they exist at the physiological pH inside cells—as the amine (A- = RNH2), or as the ammonium ion (HA = RNH3+) Let s take a 0.0010 Vf solution of methylamine at pH = 7.3, for example. According to Table 24.1, the pKa of methvlammonium ion is 10.64, so from the Henderson-Hasselbalch equation, we have... 

The ions dealt with to this point (e.g., Na+, Cl-) are monatomic that is, they are derived from a single atom by the loss or gain of electrons. Many of the most important ions in chemistry are polyatomic, containing more than one atom. Examples include the hydroxide ion (OH-) and the ammonium ion (NH ). In these and other polyatomic ions, the atoms are held together by covalent bonds, for example,... 

Notice that in each case the oxygen or nitrogen atom is surrounded by eight valence electrons. In each species, a single electron pair is shared between two bonded atoms. These bonds are called single bonds. There is one single bond in the OH- ion, two in the H20 molecule, three in NH3, and four in NH4+. There are three unshared pairs in the hydroxide ion, two in the water molecule, one in the ammonia molecule, and none in the ammonium ion. 

Cations. The ammonium ion, NH,+, behaves as a weak acid in water a 0.10 M solution of NH4CI has a pH of about 5. The process by which the NH4+ ion lowers the pH of water can be represented by the (Bransted-Lowry) equation ... 

Acidic ion Ion that forms H+ ions in water. The ammonium ion is acidic because of the reaction NHi+(flq) — ... 

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