Ammonium

Source: Wikipedia, the free encyclopedia.
This article is about the ammonium ion. For its neutral conjugate base, see ammonia.
This article is about the molecular ion. For the ancient city, see Siwa Oasis.
Ammonium
2-D skeletal version of the ammonium ion
Ball-and-stick model of the ammonium cation
Space-filling model of the ammonium cation
Names
IUPAC name
Ammonium ion
Systematic IUPAC name
Azanium[1]
Identifiers
3D model (
JSmol
)
ChEBI
ChemSpider
MeSH D000644
UNII
  • InChI=1S/H3N/h1H3/p+1
    Key: QGZKDVFQNNGYKY-UHFFFAOYSA-O
  • InChI=1/H3N/h1H3/p+1
    Key: QGZKDVFQNNGYKY-IKLDFBCSAZ
  • [NH4+]
Properties
[NH4]+
Molar mass 18.039 g·mol−1
Acidity (pKa) 9.25
Conjugate base
 Ammonia
Structure
Tetrahedral
Related compounds
Other cations
[H3]+
Related compounds
 Ammonium radical •NH4
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

The ammonium

atoms are replaced by organic
or other groups (indicated by R).

Acid–base properties

Fumes from hydrochloric acid and ammonia forming a white cloud of ammonium chloride

The ammonium ion is generated when ammonia, a weak base, reacts with

Brønsted acids (proton
donors):

H+ + NH3 → [NH4]+

The ammonium ion is mildly acidic, reacting with Brønsted bases to return to the uncharged ammonia molecule:

[NH4]+ + B− → HB + NH3

Thus, the treatment of concentrated solutions of ammonium salts with a strong base gives ammonia. When ammonia is dissolved in water, a tiny amount of it converts to ammonium ions:

H2O + NH3 ⇌ OH− + [NH4]+

The degree to which ammonia forms the ammonium ion depends on the

hydroxide ions is high), the equilibrium shifts to the left: the hydroxide
ion abstracts a proton from the ammonium ion, generating ammonia.

Formation of ammonium compounds can also occur in the vapor phase; for example, when ammonia vapor comes in contact with hydrogen chloride vapor, a white cloud of ammonium chloride forms, which eventually settles out as a solid in a thin white layer on surfaces.

Salts and characteristic reactions

Formation of ammonium

Ammonium cation is found in a variety of

soluble in water. An exception is ammonium hexachloroplatinate, the formation of which was once used as a test for ammonium. The ammonium salts of nitrate and especially perchlorate
are highly explosive, in these cases, ammonium is the reducing agent.

In an unusual process, ammonium ions form an amalgam. Such species are prepared by the addition of sodium amalgam to a solution of ammonium chloride.[2] This amalgam eventually decomposes to release ammonia and hydrogen.[3]

To find whether the ammonium ion is present in the salt, first, the salt is heated in presence of alkali hydroxide releasing a gas with a characteristic smell, which is ammonia.

[NH4]+ + OH− heat→ NH3 + H2O

To further confirm ammonia, it passed through a glass rod dipped in an HCl solution (hydrochloric acid), creating white dense fumes of ammonium chloride.

NH3(g) + HCl(aq) → [NH4]Cl(s)

Ammonia, when passed through CuSO4 (copper(II) sulfate) solution, changes its color from blue to deep blue, forming Schweizer's reagent.

CuSO4(aq) + 4 NH3(aq) + 4 H2O → [Cu(NH3)4(H2O)2](OH)2(aq) + H2SO4(aq)

Ammonia or ammonium ion when added to

Nessler's reagent
gives a brown color precipitate known as the iodide of Million's base in basic medium.

Ammonium ion when added to chloroplatinic acid gives a yellow precipitate of ammonium hexachloroplatinate(IV).

H2[PtCl6](aq) + [NH4]+(aq) → [NH4]2[PtCl6](s) + 2 H+

Ammonium ion when added to

sodium cobaltinitrite
gives a yellow precipitate of ammonium cobaltinitrite.

Na3[Co(NO2)6](aq) + 3 [NH4]+(aq) → [NH4]3[Co(NO2)6](s) + 3 Na+(aq)

Ammonium ion gives a white precipitate of ammonium bitartrate when added to potassium bitartrate.

KC4H5O6(aq) + [NH4]+(aq) → [NH4]C4H5O6(s) + K+(aq)

Structure and bonding

The lone electron pair on the nitrogen atom (N) in ammonia, represented as a line above the N, forms a coordinate bond with a proton (H+). After that, all four N−H bonds are equivalent, being polar covalent bonds. The ion has a tetrahedral structure and is isoelectronic with methane and the borohydride anion. In terms of size, the ammonium cation (rionic = 175 pm)[citation needed] resembles the caesium cation (rionic = 183 pm).[citation needed]

Organic ions

See also: Amine

The hydrogen atoms in the ammonium ion can be substituted with an

IUPAC nomenclature: aminium ion). Depending on the number of organic groups, the ammonium cation is called a primary, secondary, tertiary, or quaternary
. Except the quaternary ammonium cations, the organic ammonium cations are weak acids.

An example of a reaction forming an ammonium ion is that between

dimethylammonium
cation, [(CH3)2NH2]+:

Quaternary ammonium cations have four organic groups attached to the nitrogen atom, they lack a hydrogen atom bonded to the nitrogen atom. These cations, such as the

phase-transfer catalysts and surfactants
.

An unusual class of organic ammonium salts is derivatives of amine radical cations, [•NR3]+ such as tris(4-bromophenyl)ammoniumyl hexachloroantimonate.

Biology

Main article: Excretion

Ammonium ions are a waste product of the

reptiles, and terrestrial snails, metabolic ammonium is converted into uric acid, which is solid and can therefore be excreted with minimal water loss.[5]

Ammonium is an important source of nitrogen for many plant species, especially those growing on hypoxic soils.[4] However, it is also toxic to most crop species and is rarely applied as a sole nitrogen source.[6]

Metal

The ammonium cation has very similar properties to the heavier

electrons) at very high pressures, such as inside giant gas planets such as Uranus and Neptune.[8][9]

Under normal conditions, ammonium does not exist as a pure metal but does as an amalgam (alloy with mercury).[10]

See also

References

  1. ISBN 0-85404-438-8. pp. 71,105,314. Electronic version.
  2. ^ "Pseudo-binary compounds". Archived from the original on 2020-07-27. Retrieved 2007-10-12.
  3. ^ "Ammonium Salts". VIAS Encyclopedia.
  4. ^
    ISBN 978-0-12-814608-8.{{cite book}}: CS1 maint: date and year (link
    )
  5. ISBN 978-0-8053-6624-2
    .
  6. doi:10.1078/0176-1617-0774
    .
  7. ISBN 0-12-352651-5
  8. ^
    S2CID 4199721
    .
  9. ^
    doi:10.1093/mnras/114.2.172
    .
  10. doi:10.1021/ed006p1767
    .
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