Everything about Lead Ii Nitrate totally explained
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Lead(II) nitrate is an
inorganic compound with the
chemical formula Pb(NO
3)
2. It commonly occurs as a colourless
crystal or white powder and, unlike most other lead(II)
salts, is
soluble in
water.
Known since the
Middle Ages by the name
plumb dulcis, the production of lead(II) nitrate from either metallic
lead or
lead oxide in
nitric acid was small-scale, for direct use in making other
lead compounds. In the 19th century lead(II) nitrate began to be produced commercially in Europe and the United States. Historically, the main use was as a raw material in the production of
pigments for
lead paints, but such paints have been superseded by less toxic paints based on
titanium dioxide. Other industrial uses included heat
stabilisation in
nylon and
polyesters, and in coatings of
photothermographic paper. Since around the year 2000, lead(II) nitrate has begun to be used in
gold cyanidation.
Lead(II) nitrate is
toxic, an
oxidising agent, and is categorised as
probably carcinogenic to humans by the
International Agency for Research on Cancer. Consequently, it must be handled and stored with the appropriate safety precautions to prevent inhalation, ingestion and skin contact. Due to its
hazardous nature, the limited applications of lead(II) nitrate are under constant scrutiny.
History
Since the Middle Ages, lead(II) nitrate has been produced as a raw material for the production of coloured pigments in
lead paints, such as
chrome yellow (lead(II) chromate),
chrome orange (lead(II) hydroxide chromate) and similar
lead compounds. These pigments were used for
dyeing and printing
calico and other textiles.
In 1597, the German
alchemist Andreas Libavius first described the compound, coining the medieval names of
plumb dulcis and
calx plumb dulcis, meaning "sweet lead", because of its taste. Although originally not understood during the following centuries, the
decrepitation property of lead(II) nitrate led to its use in matches and special
explosives such as
lead azide.
The production process was and still is chemically straightforward, effectively dissolving
lead in aqua fortis (
nitric acid), and subsequently harvesting the
precipitate. However, the production remained small-scale for many centuries, and the commercial production of lead(II) nitrate as raw material for the manufacture of other lead compounds wasn't reported until 1835. In 1974, the
U.S. consumption of lead compounds, excluding pigments and
gasoline additives, was 642 tonnes.
Chemistry
Aqueous chemistry
Lead(II) nitrate readily
dissolves in water to give a clear, colourless solution. As an
ionic substance, the dissolution of lead(II) nitrate involves
dissociation into its constituent ions.
» Pb(NO
3)
2(
s) → Pb
2+(
aq) + 2 NO
3−(aq)
Any
solution containing the lead(II) cation will react with a solution containing the
iodide anion to produce a
precipitate of the bright orange-yellow
lead(II) iodide. This reaction is often used to demonstrate precipitation, because of the striking colour change observed, under the name
Pot-o-Gold or
Golden Rain:
» Pb
2+(aq) + 2 I
−(aq) → PbI
2(s)
Similar
metathesis reactions take place in the solid phase when appropriate solids, such as
potassium iodide and lead(II) nitrate, are mixed and finely ground using a
mortar and pestle.
» Pb(NO
3)
2(s) + 2 KI(s) → PbI
2(s) + 2 KNO
3(s)
The colour of the resulting mixture will depend on the relative amount of the
reactants used, and the extent of grinding; in any event, the colour will be paler than that of pure lead(II) iodide due to the presence of white solids within the mixture.
Apart from lead(II) nitrate,
lead(II) acetate is the only other common soluble lead compound. Nearly all other lead compounds are insoluble in water, even when coupled with commonly very soluble anions. For example,
lead(II) chloride,
lead(II) bromide and
lead(II) iodide, collectively known as lead
halides, are merely weakly soluble in water (less than 0.01 mol/l) at room temperature, and only slightly more closer to the boiling point. This means that lead(II) nitrate has particular importance as a starting point for the production of insoluble lead compounds via
double decomposition.
Hot solutions of lead halides can be brought to precipitation on cooling to create feathery, iridescent crystals suspended in water, the colour of which crystal depends on the particular halide (chloride =
white, bromide =
buff, iodide =
yellow). These crystals appear suddenly, requiring only a
nucleation site once the temperature of the solution has fallen sufficiently for the solution to be
supersaturated. This effect is used for demonstration of solubility in classrooms.
When concentrated
sodium hydroxide solution is added to lead(II) nitrate solution,
basic nitrates are formed, even well past the
equivalence point. Up through the half equivalence point, Pb(NO
3)
2·Pb(OH)
2 predominates, then after this point Pb(NO
3)
2·5Pb(OH)
2 is formed. No simple Pb(OH)
2 is formed up to at least
pH 12.
Crystal structure
The
crystal structure of solid lead(II) nitrate has been determined by
neutron diffraction. The compound
crystallises in the cubic system with the lead atoms in a
face-centered cubic system. Its
space group is Pa3
Z=4 (
Bravais lattice notation), with each side of the cube with length 784
picometres.
The black dots represent the lead atoms, the white dots the nitrate groups 27 picometres above the plane of the lead atoms, and the blue dots the nitrate groups the same distance below this plane. In this configuration, every lead atom is
bonded to twelve oxygen atoms (
bond length: 281 pm). All N–O bond lengths are identical, at 127 picometres.
Research interest in the crystal structure of lead(II) nitrate was partly based on the possibility of free internal rotation of the nitrate groups within the crystal lattice at elevated temperatures, but this didn't materialise. In the crystal structure for this compound, the EO
5 chain is wrapped around the lead ion in an
equatorial plane similar to that of a
crown ether. The two bidentate nitrate
ligands are in
trans configuration. The total
coordination number is 10, with the lead ion in a bicapped
square antiprism molecular geometry.
The complex formed by lead(II) nitrate,
lead(II) perchlorate and a
bithiazole bidentate N-donor ligand is binuclear, with a nitrate group bridging the lead atoms with coordination number of 5 and 6. One interesting aspect of this type of complexes is the presence of a physical gap in the
coordination sphere, for example, the ligands are not placed symmetrically around the metal ion. This is potentially due to a lead
lone pair of electrons, also found in lead complexes with an
imidazole ligand.
This type of chemistry isn't unique to the nitrate salt; other lead(II) compounds such as
lead(II) bromide also form complexes, but the nitrate is frequently used because of its solubility properties and its bidentate nature.
Oxidation and decrepitation
Lead(II) nitrate is an
oxidising agent. Depending on the reaction, this may be due to the Pb
2+(aq) ion, which has a standard
reduction potential (E
0) of −0.125 V, or the nitrate ion, which under acidic conditions has an E
0 of +0.956 V.
When heated, lead(II) nitrate crystals decompose to
lead(II) oxide,
dioxygen and
nitrogen dioxide, accompanied by a crackling noise. This effect is referred to as
decrepitation.
» 2 Pb(
NO3)
2(s) → 2
PbO(s) + 4
NO2(
g) +
O2(g)
Because of this property, lead nitrate is sometimes used in
pyrotechnics such as
fireworks.
Applications
Due to the hazardous nature of lead(II) nitrate, there's a preference for using alternatives in industrial applications. In the formerly major application of
lead paints, it has largely been replaced by
titanium dioxide. Other historical applications of lead(II) nitrate, such as in matches and fireworks, have declined or ceased as well. Current applications of lead(II) nitrate include use as a heat stabiliser in nylon and polyesters, as a coating for
photothermographic paper, and in
rodenticides. Both the cyanidation itself, as well as the use of lead compounds in the process, are deemed controversial due to the compounds' toxic nature.
Safety
Lead(II) nitrate is toxic, and ingestion may lead to acute lead poisoning, as is applicable for all soluble lead compounds. All
inorganic lead compounds are classified by the
International Agency for Research on Cancer (IARC) as
probably carcinogenic to humans (Category 2A). They have been linked to
renal cancer and
glioma in experimental animals and to renal cancer,
brain cancer and
lung cancer in humans, although studies of workers exposed to lead are often complicated by concurrent exposure to
arsenic. Lead is known to substitute for
zinc in a number of
enzymes, including
δ-aminolevulinic acid dehydratase (porphobilinogen synthase) in the
heme biosynthetic pathway and
pyrimidine-5′-nucleotidase, important for the correct metabolism of
DNA.
To prevent inhalation, ingestion and exposure to skin, lead(II) nitrate must be handled in a fume cupboard, with face, body and hand protection. Special instructions for handling are included in all
Material safety data sheets (MSDS). After use, all material and its containers must be disposed of as
hazardous waste. Spillage and release to the environment must be avoided.
Further Information
Get more info on 'Lead Ii Nitrate'.
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