also used in forensic science to develop latent Üngerprints.
niobium Symbol Nb. A soft ductile
grey-blue metallic transition element; a.n. 41; r.a.m. 92.91; r.d. 8.57;
m.p. 2468°C; b.p. 4742°C. It occurs in
several minerals, including niobite
(Fe(NbO 3 ) 2 ), and is extracted by several methods including reduction of
the complex Ûuoride K 2 NbF 7 using
sodium. It is used in special steels
and in welded joints (to increase
strength). Niobium–zirconium alloys
are used in superconductors. Chemically, the element combines with the
halogens and oxidizes in air at 200°C.
It forms a number of compounds and
complexes with the metal in oxidation states 2, 3, or 5. The element
was discovered by Charles Hatchett
(c. 1765–1847) in 1801 and Ürst isolated by Christian Blomstrand
(1826–97) in 1864. Formerly, it was
called columbium.
A
• Information from the WebElements site
nitrate A salt or ester of nitric acid.
nitrating mixture A mixture of
concentrated sulphuric and nitric
acids, used to introduce a nitro group
(–NO 2 ) into an organic compound. Its
action depends on the presence of
the nitronium ion, NO 2
+ . It is mainly
used to introduce groups into the
molecules of *aromatic compounds
(the nitro group can subsequently be
converted into or replaced by others)
and to make commercial *nitro compounds, such as the explosives cellulose trinitrate (nitrocellulose),
glyceryl trinitrate (nitroglycerine),
trinitrotoluene (TNT), and picric acid
(trinitrophenol).
nitration A type of chemical reaction in which a nitro group (–NO 2 ) is
added to or substituted in a molecule. Nitration can be carried out by
a mixture of concentrated nitric and
sulphuric acids (see nitrating mixture).
nitre (saltpetre) Commercial *potassium nitrate; the name was formerly
applied to natural crustlike efÛorescences, occurring in some arid regions.
nitre cake See sodium hydrogensulphate.
nitrene A species of the type HN: or
RN:, analogous to a *carbene. The nitrogen atom has four nonbonding
electrons, two of which are a lone
pair. The other two may have parallel spins (a triplet state) or antiparallel spins (a singlet state).
nitric acid A colourless corrosive
poisonous liquid, HNO 3 ; r.d. 1.50;
m.p. –42°C; b.p. 83°C. Nitric acid may
be prepared in the laboratory by the
distillation of a mixture of an alkalimetal nitrate and concentrated
sulphuric acid. The industrial production is by the oxidation of ammonia to nitrogen monoxide, the
oxidation of this to nitrogen dioxide,
and the reaction of nitrogen dioxide
with water to form nitric acid and nitrogen monoxide (which is recycled).
The Ürst reaction (NH 3 to NO) is
catalysed by platinum or platinum/
rhodium in the form of Üne wire
gauze. The oxidation of NO and the
absorption of NO 2 to form the product are noncatalytic and proceed
with high yields but both reactions
are second-order and slow. Increases
in pressure reduce the selectivity of
the reaction and therefore rather
large gas absorption towers are required. In practice the absorbing acid
is refrigerated to around 2°C and a
commercial ‘concentrated nitric acid’
at about 67% is produced.
Nitric acid is a strong acid (highly
dissociated in aqueous solution) and
dilute solutions behave much like
other mineral acids. Concentrated niniobium
372
n
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niobium Symbol Nb. A soft ductile
grey-blue metallic transition element; a.n. 41; r.a.m. 92.91; r.d. 8.57;
m.p. 2468°C; b.p. 4742°C. It occurs in
several minerals, including niobite
(Fe(NbO 3 ) 2 ), and is extracted by several methods including reduction of
the complex Ûuoride K 2 NbF 7 using
sodium. It is used in special steels
and in welded joints (to increase
strength). Niobium–zirconium alloys
are used in superconductors. Chemically, the element combines with the
halogens and oxidizes in air at 200°C.
It forms a number of compounds and
complexes with the metal in oxidation states 2, 3, or 5. The element
was discovered by Charles Hatchett
(c. 1765–1847) in 1801 and Ürst isolated by Christian Blomstrand
(1826–97) in 1864. Formerly, it was
called columbium.
A
• Information from the WebElements site
nitrate A salt or ester of nitric acid.
nitrating mixture A mixture of
concentrated sulphuric and nitric
acids, used to introduce a nitro group
(–NO 2 ) into an organic compound. Its
action depends on the presence of
the nitronium ion, NO 2
+ . It is mainly
used to introduce groups into the
molecules of *aromatic compounds
(the nitro group can subsequently be
converted into or replaced by others)
and to make commercial *nitro compounds, such as the explosives cellulose trinitrate (nitrocellulose),
glyceryl trinitrate (nitroglycerine),
trinitrotoluene (TNT), and picric acid
(trinitrophenol).
nitration A type of chemical reaction in which a nitro group (–NO 2 ) is
added to or substituted in a molecule. Nitration can be carried out by
a mixture of concentrated nitric and
sulphuric acids (see nitrating mixture).
nitre (saltpetre) Commercial *potassium nitrate; the name was formerly
applied to natural crustlike efÛorescences, occurring in some arid regions.
nitre cake See sodium hydrogensulphate.
nitrene A species of the type HN: or
RN:, analogous to a *carbene. The nitrogen atom has four nonbonding
electrons, two of which are a lone
pair. The other two may have parallel spins (a triplet state) or antiparallel spins (a singlet state).
nitric acid A colourless corrosive
poisonous liquid, HNO 3 ; r.d. 1.50;
m.p. –42°C; b.p. 83°C. Nitric acid may
be prepared in the laboratory by the
distillation of a mixture of an alkalimetal nitrate and concentrated
sulphuric acid. The industrial production is by the oxidation of ammonia to nitrogen monoxide, the
oxidation of this to nitrogen dioxide,
and the reaction of nitrogen dioxide
with water to form nitric acid and nitrogen monoxide (which is recycled).
The Ürst reaction (NH 3 to NO) is
catalysed by platinum or platinum/
rhodium in the form of Üne wire
gauze. The oxidation of NO and the
absorption of NO 2 to form the product are noncatalytic and proceed
with high yields but both reactions
are second-order and slow. Increases
in pressure reduce the selectivity of
the reaction and therefore rather
large gas absorption towers are required. In practice the absorbing acid
is refrigerated to around 2°C and a
commercial ‘concentrated nitric acid’
at about 67% is produced.
Nitric acid is a strong acid (highly
dissociated in aqueous solution) and
dilute solutions behave much like
other mineral acids. Concentrated niniobium
372
n
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