Phosphate
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Phosphate
Systematic name[hide]
Phosphate[1]
Identifiers
CAS number
14265-44-2
PubChem
1061
ChemSpider
1032
UNII
NK08V8K8HR
MeSH
Phosphates
ChEBI
CHEBI:18367
ChEMBL
CHEMBL289287
Beilstein Reference
3903772
Gmelin Reference
1997
Jmol-3D images
Image 1
Image 2
Image 3
SMILES
[show]
InChI
[show]
Properties
Molecular formula
PO43-
Molar mass
94.9714 g mol−1
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Except where noted otherwise, data are given for materials in their standard state (at 25 °C,
100 kPa)
Infobox references
A phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate,
ororganophosphate, is an ester of phosphoric acid. Organic phosphates are important
in biochemistry andbiogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use
in agriculture and industry.[2] At elevated temperatures in the solid state, phosphates can condense to
form pyrophosphates.
Contents
[hide]

1 Chemical properties
o
1.1 Biochemistry of phosphates

2 Occurrence and mining

3 Ecology

4 See also

5 References

6 External links
Chemical properties [edit]
This is the structural formula of the phosphoric acid functional group as found in weakly acidicaqueous solution. In more basicaqueous solutions, the group
donates the two hydrogen atomsand ionizes as a phosphate group with a negative charge of 2. [3]
The phosphate ion is a polyatomic ion with the empirical formula PO3−
4
and a molar mass of 94.97 g/mol. It consists of one central phosphorus atom surrounded by four oxygen
atoms in a tetrahedral arrangement. The phosphate ion carries a negative three formal charge and is
the conjugate base of the hydrogen phosphate ion,HPO2−
4,
which is the conjugate base of H2PO−
4,
the dihydrogen phosphate ion, which in turn is the conjugate base of H3PO4, phosphoric acid. A phosphate
salt forms when a positively charged ion attaches to the negatively charged oxygen atoms of the ion, forming
an ionic compound. Many phosphates are not soluble in water atstandard temperature and pressure. The
sodium, potassium, rubidium, caesium and ammonium phosphates are all water soluble. Most other
phosphates are only slightly soluble or are insoluble in water. As a rule, the hydrogen and dihydrogen
phosphates are slightly more soluble than the corresponding phosphates. Thepyrophosphates are mostly water
soluble.
Aqueous phosphate exists in four forms. In strongly basic conditions, the phosphate ion (PO3−
4)
predominates, whereas in weakly basic conditions, the hydrogen phosphate ion (HPO2−
4)
is prevalent. In weakly acid conditions, the dihydrogen phosphate ion (H2PO−
4)
is most common. In strongly acidic conditions, trihydrogen phosphate (H3PO4) is the main form.

H3PO4
Phosphoric acid

H2PO−
4
Dihydrogen phosphate

HPO2−
4
Hydrogen phosphate

PO3−
4
Phosphate
More precisely, considering the following three equilibrium reactions:
H3PO4
H+ + H2PO−
4
H2PO−
4
H+ + HPO2−
4
HPO2−
4
H+ + PO3−
4
the corresponding constants at 25°C (in mol/L) are (see phosphoric acid):
(pKa1 2.12)
(pKa2 7.21)
(pKa3 12.67)
The speciation diagram obtained using these pK values shows three distinct
regions. In effect H3PO4, H2PO−
4
andHPO2−
4
behave as separate weak acids. This is because the successive pK values differ
by more than 4. For each acid the pH at half-neutralization is equal to the pK value
of the acid. The region in which the acid is in equilibrium with its conjugate base is
defined by pH ≈ pK ± 2. Thus the three pH regions are approximately 0–4, 5–9 and
10–14. This is idealized as it assumes constant ionic strength, which will not hold in
reality at very low and very high pH values.
For a neutral pH as in the cytosol, pH=7.0
so that only H2PO−
4
and HPO2−
4
ions are present in significant amounts (62% H2PO−
4,
4
38% HPO2−
Note that in the extracellular fluid (pH=7.4), this proportion is inverted
(61% HPO2−
4,
39% H2PO−
4).
Phosphate can form many polymeric ions such as diphosphate (also known
as pyrophosphate), P2O4−
7,
andtriphosphate, P3O5−
10.
The various metaphosphate ions (which are usually long linear polymers)
have an empirical formula of PO−
3
and are found in many compounds.
Biochemistry of phosphates [edit]
In biological systems, phosphorus is found as a free phosphate ion in solution
and is called inorganic phosphate, to distinguish it from phosphates bound in
various phosphate esters. Inorganic phosphate is generally denoted Pi and at
physiological (neutral) pH primarily consists of a mixture of HPO2−
4
and H2PO−
4
ions.
Inorganic phosphate can be created by the hydrolysis of pyrophosphate, which
is denoted PPi:
P2O4−
7
+ H2O
2 HPO2−
4
However, phosphates are most commonly found in the form of adenosine
phosphates, (AMP, ADP and ATP) and in DNA and RNA and can be
released by the hydrolysis of ATP or ADP. Similar reactions exist for the
other nucleoside diphosphates and triphosphates. Phosphoanhydride
bonds in ADP and ATP, or other nucleoside diphosphates and
triphosphates, contain high amounts of energy which give them their vital
role in all living organisms. They are generally referred to as high energy
phosphate, as are the phosphagens in muscle tissue. Compounds such as
substituted phosphines have uses in organic chemistry but do not seem to
have any natural counterparts.
The addition and removal of phosphate from proteins in all cells is a pivotal
strategy in the regulation of metabolic processes.
Reference ranges for blood tests, showing inorganic phosphorus in purple at right, being almost identical to
the molar concentration of phosphate.
Phosphate is useful in animal cells as a buffering agent. Phosphate salts
that are commonly used for preparing buffer solutions at cell pHs include
Na2HPO4, NaH2PO4, and the corresponding potassium salts.
An important occurrence of phosphates in biological systems is as the
structural material of bone and teeth. These structures are made of
crystalline calcium phosphate in the form of hydroxyapatite. The hard
dense enamel of mammalian teeth consists of fluoroapatite, an hydroxy
calcium phosphate where some of thehydroxyl groups have been replaced
by fluoride ions.
Occurrence and mining [edit]
Phosphate mine near Flaming Gorge, Utah, 2008
Train loaded with phosphate rock,Metlaoui, Tunisia, 2012.
Phosphates are the naturally occurring form of the elementphosphorus,
found in many phosphate minerals. In mineralogy and geology, phosphate
refers to a rock or ore containing phosphate ions. Inorganic phosphates
are mined to obtain phosphorus for use in agriculture and industry.[2]
The largest phosphorite or rock phosphate deposits in North Americalie in
the Bone Valley region of central Florida, United States, the Soda Springs
region of Idaho, and the coast of North Carolina. Smaller deposits are
located in Montana, Tennessee, Georgia and South Carolina near
Charleston along Ashley Phosphate road. The small island nation
of Nauru and its neighbor Banaba Island, which used to have massive
phosphate deposits of the best quality, have been mined excessively.
Rock phosphate can also be found in Egypt, Israel, Morocco, Navassa
Island, Tunisia, Togo and Jordan, countries that have large phosphate
mining industries.
Phosphorite mines are primarily found in:

North America: United States of America, especially Florida, with
lesser deposits in North Carolina, Idaho andTennessee.

Africa: Egypt, Morocco, mainly
near Khouribga and Youssoufia; Senegal, Togo, Tunisia and Western
Sahara, at the town of Bu Craa.

Middle East: Israel, Saudi Arabia, Jordan, and Iraq, at the town
of Akashat, near the Jordanian border.

Oceania: Australia, Makatea, Nauru, and Banaba Island.
In 2007, at the current rate of consumption, the supply of phosphorus was
estimated to run out in 345 years.[4]However, some scientists now believe
that a "peak phosphorus" will occur in 30 years and that at "current rates,
reserves will be depleted in the next 50 to 100 years."[5] Reserves refer to
the amount assumed recoverable at current market prices, and, in 2012,
the USGS estimated 71 billion tons of world reserves, while 0.19 billion
tons were mined globally in 2011.[6] Phosphorus comprises 0.1% by mass
of the average rock[7](while, for perspective, its typical concentration in
vegetation is 0.03% to 0.2%),[8] and consequently there are quadrillions of
tons of phosphorus in Earth's 3 * 1019 ton crust,[9] albeit at predominantly
lower concentration than the deposits counted as reserves from being
inventoried and cheaper to extract.
Some phosphate rock deposits are notable for their inclusion of significant
quantities of radioactive uranium isotopes. This syndrome is noteworthy
because radioactivity can be released into surface waters[10] in the process
of application of the resultant phosphate fertilizer (e.g. in many tobacco
farming operations in the southeast USA).
In December 2012 Cominco Resources announced an updated JORC
compliant resource of their Hinda project of 531Mt making it the largest
measured and indicated phosphate deposit in the world.[11]
Ecology [edit]
Sea surface phosphate from the World Ocean Atlas.
In ecological terms, because of its important role in biological systems,
phosphate is a highly sought after resource. Once used, it is often a
limiting nutrient in environments, and its availability may govern the rate of
growth of organisms. This is generally true of freshwater environments,
whereas nitrogen is more often the limiting nutrient in marine (seawater)
environments. Addition of high levels of phosphate to environments and to
micro-environments in which it is typically rare can have significant
ecological consequences. For example, blooms in the populations of some
organisms at the expense of others, and the collapse of populations
deprived of resources such as oxygen (seeeutrophication) can occur. In
the context of pollution, phosphates are one component of total dissolved
solids, a major indicator of water quality, but not all phosphorus is in a
molecular form which algae can break down and consume.[12]
Calcium hydroxyapatite and calcite precipitates can be found around
bacteria in alluvial topsoil.[13] As clay minerals promote biomineralization,
the presence of bacteria and clay minerals resulted in calcium
hydroxyapatite and calcite precipitates.[13]
Phosphate deposits can contain significant amounts of naturally occurring
heavy metals. Mining operations processing phosphate rock can leave
tailings piles containing elevated levels
of cadmium, lead, nickel, copper, chromium, and uranium. Unless carefully
managed, these waste products can leach heavy metals into groundwater
or nearby estuaries. Uptake of these substances by plants and marine life
can lead to concentration of toxic heavy metals in food products.[14]
In Germany, the use of uranium-contaminated standard phosphate
fertilizers in farming has been linked to significantly raised uranium levels
in drinking water.[15]In some areas, it has led to recommendations to use
bottled water, instead of tap water, to prepare food for babies and small
children.