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| RTECS = TB6300000
| RTECS = TB6300000
}}|Section2={{Chembox Properties
}}|Section2={{Chembox Properties
| Formula = {{Chem|H|3|PO|4}}
| Formula = {{chem2|H3PO4}}
| H=3 | P=1 | O=4
| H=3|P=1|O=4
| Appearance = white solid  
| Appearance = Colorless solid  
| Odor = Odorless
| Odor = Odorless
| Density = 1.6845 {{nbsp}}g⋅cm<sup>−3</sup> (25&nbsp;°C, 85%),<ref name="Density 85%">
| Density = 1.6845 g/cm<sup>3</sup> (25&nbsp;°C, 85%),<ref name="Density 85%">
   {{Cite journal
   {{Cite journal
   | author=Christensen, J. H.
   | author=Christensen, J. H.
Line 42: Line 42:
   | volume=47 | issue=6 | pages=1277–1280
   | volume=47 | issue=6 | pages=1277–1280
   | doi=10.1021/ie50546a061
   | doi=10.1021/ie50546a061
   }}</ref> 1.834 {{nbsp}}g⋅cm<sup>−3</sup> (solid)<ref name="Density solid">{{Cite web
   }}</ref> 1.834 g/cm<sup>3</sup> (solid)<ref name="Density solid">{{Cite web
   | url=https://cameochemicals.noaa.gov/chemical/4231
   | url=https://cameochemicals.noaa.gov/chemical/4231
   | title=CAMEO Chemicals Datasheet – Phosphoric Acid
   | title=CAMEO Chemicals Datasheet – Phosphoric Acid
Line 144: Line 144:
}}
}}


'''Phosphoric acid''' (orthophosphoric acid, monophosphoric acid or phosphoric(V) acid), is a [[weak acid]] with the [[chemical formula]] {{chem|[[Hydrogen|H]]|3|[[phosphorus|P]]|[[oxygen|O]]|4}}. The pure compound is a colorless [[solid]].
'''Phosphoric acid''' (orthophosphoric acid, monophosphoric acid or phosphoric(V) acid) is an [[inorganic compound]] with the [[chemical formula]] {{chem2|[[Hydrogen|H]]3[[phosphorus|P]][[oxygen|O]]4}}. Phosphoric acid is a colorless [[solid]], it is commonly encountered as an 85% [[aqueous solution]], which is a colourless, odourless, and non-[[volatility (chemistry)|volatile]] syrupy liquid. It is a major industrial chemical, being a component of many fertilizers.


All three hydrogens are [[acid]]ic to varying degrees and can be lost from the [[molecule]] as H<sup>+</sup> ions ([[protons]]). When all three H<sup>+</sup> ions are removed, the result is an [[phosphate|orthophosphate]] ion PO<sub>4</sub><sup>3−</sup>, commonly called "phosphate". Removal of one or two protons gives [[phosphate|dihydrogen phosphate]] ion {{chem|H|2|PO|4|−}}, and the [[phosphate|hydrogen phosphate]] ion {{chem|HPO|4|2−}}, respectively. Orthophosphoric acid also forms [[esters]], called [[organophosphate]]s.<ref name="Westheimer">{{Cite journal|last=Westheimer |first=F.H. |author-link=Frank Westheimer |title=Why nature chose phosphates |journal=[[Science (journal)|Science]] |volume=235 |issue=4793 |pages=1173–1178 (see pp. 1175–1176) |date=6 June 1987 |doi=10.1126/science.2434996 |bibcode=1987Sci...235.1173W|citeseerx=10.1.1.462.3441 |pmid=2434996 }}</ref>
The compound is an [[acid]]. Removal of all three {{chem2|H+}} ions gives the [[phosphate]] ion {{chem2|PO4(3−)}}. Removal of one or two protons gives [[phosphate|dihydrogen phosphate]] ion {{chem2|H2PO4−}}, and the [[phosphate|hydrogen phosphate]] ion {{chem2|HPO4(2−)}}, respectively. Phosphoric acid forms [[esters]], called [[organophosphate]]s.<ref name="Westheimer">{{Cite journal|last=Westheimer |first=F.H. |author-link=Frank Westheimer |title=Why nature chose phosphates |journal=[[Science (journal)|Science]] |volume=235 |issue=4793 |pages=1173–1178 (see pp. 1175–1176) |date=6 June 1987 |doi=10.1126/science.2434996 |bibcode=1987Sci...235.1173W|citeseerx=10.1.1.462.3441 |pmid=2434996 }}</ref>


Phosphoric acid is commonly encountered in chemical laboratories as an 85% [[aqueous solution]], which is a colourless, odourless, and non-[[volatility (chemistry)|volatile]] syrupy liquid. Although phosphoric acid does not meet the strict definition of a [[strong acid]], the 85% solution can still severely irritate the skin and damage the eyes.
The name "orthophosphoric acid" can be used to distinguish this specific acid from other "[[phosphoric acids and phosphates|phosphoric acids]]", such as [[pyrophosphoric acid]]. Nevertheless, the term "phosphoric acid" often means this specific compound; and that is the current [[IUPAC nomenclature]].


The name "orthophosphoric acid" can be used to distinguish this specific acid from other "[[phosphoric acids and phosphates|phosphoric acids]]", such as [[pyrophosphoric acid]].  Nevertheless, the term "phosphoric acid" often means this specific compound; and that is the current [[IUPAC nomenclature]].
=={{Anchor|Manufacture}}Production==
Phosphoric acid is produced industrially by one of two routes, wet processes and dry.<ref>{{cite book |last1=Becker |first1=Pierre |title=Phosphates and phosphoric acid |date=1988 |publisher=Marcel Dekker |location=New York |isbn=978-0824717124}}</ref>


==Manufacture==
=== Wet process ===
Phosphoric acid is produced industrially by two general routes.<ref>{{cite book |last1=Becker |first1=Pierre |title=Phosphates and phosphoric acid |date=1988 |publisher=Marcel Dekker |location=New York |isbn=978-0824717124}}</ref> In the wet process a phosphate-containing mineral such as calcium [[hydroxyapatite]] is treated with [[sulfuric acid]].<ref>{{Greenwood&Earnshaw2nd|pages=520–522}}</ref>
In the wet process, a phosphate-containing mineral such as calcium [[hydroxyapatite]] and [[fluorapatite]] are treated with [[sulfuric acid]].<ref>{{Greenwood&Earnshaw2nd|pages=520–522}}</ref>
: <chem>Ca5(PO4)3OH + 5H2SO4 -> 3H3PO4 + 5CaSO4v + H2O</chem>
:{{chem2|Ca5(PO4)3OH + 5 H2SO4 → 3 H3PO4 + 5 [[CaSO4]] + H2O}}
[[Fluoroapatite]] is an alternative feedstock, in which case fluoride is removed as the insoluble compound Na<sub>2</sub>SiF<sub>6</sub>. The phosphoric acid solution usually contains 23–33% P<sub>2</sub>O<sub>5</sub> (32–46% H<sub>3</sub>PO<sub>4</sub>). It may be concentrated to produce ''commercial-'' or ''merchant-grade'' phosphoric acid, which contains about 54–62% [[P2O5|P<sub>2</sub>O<sub>5</sub>]] (75–85% H<sub>3</sub>PO<sub>4</sub>). Further removal of water yields ''superphosphoric acid'' with a P<sub>2</sub>O<sub>5</sub> concentration above 70% (corresponding to nearly 100% H<sub>3</sub>PO<sub>4</sub>). [[Calcium sulfate]] (gypsum) is produced as a by-product and is removed as [[phosphogypsum]].
:{{Chem2|Ca5(PO4)3F + 5 H2SO4 → 3 H3PO4 + 5 [[CaSO4]] + HF}}


To produce food-grade phosphoric acid, phosphate ore is first reduced with [[Coke (fuel)|coke]] in an [[electric arc furnace]], to make elemental [[phosphorus]]. Silica is also added, resulting in the production of [[calcium silicate]] slag. Elemental phosphorus is distilled out of the furnace and burned with air to produce high-purity [[phosphorus pentoxide]], which is dissolved in water to make phosphoric acid.
[[Calcium sulfate]] (gypsum, {{Chem2|CaSO4}}) is a by-product, which is removed as [[phosphogypsum]]. The [[hydrogen fluoride]] (HF) gas is streamed into a [[Wet scrubber|wet (water) scrubber]] producing [[hydrofluoric acid]]. In both cases the phosphoric acid solution usually contains 23–33%  P2O5 (32–46% {{chem2|H3PO4}}). It may be concentrated to produce ''commercial-'' or ''merchant-grade'' phosphoric acid, which contains about 54–62% [[Phosphorus pentoxide|{{chem2|P2O5}}]] (75–85% {{chem2|H3PO4}}). Further removal of water yields ''superphosphoric acid'' with a {{chem2|P2O5}} concentration above 70% (corresponding to nearly 100% {{chem2|H3PO4}}). The phosphoric acid from both processes may be further purified by removing compounds of arsenic and other potentially toxic impurities.
 
=== Dry process===
The phosphoric acid from both processes may be further purified by removing compounds of arsenic and other potentially toxic impurities.
To produce food-grade phosphoric acid, phosphate ore is first reduced with [[Coke (fuel)|coke]] in an [[electric arc furnace]], to give elemental [[phosphorus]]. Silica is also added, resulting in the production of [[calcium silicate]] slag. Elemental phosphorus is distilled out of the furnace and burned with air to produce high-purity [[phosphorus pentoxide]], which is dissolved in water to make phosphoric acid.<ref>{{cite journal |doi=10.1021/acscentsci.0c00332|title=Let's Make White Phosphorus Obsolete |year=2020 |last1=Geeson |first1=Michael B. |last2=Cummins |first2=Christopher C. |journal=ACS Central Science |volume=6 |issue=6 |pages=848–860 |pmid=32607432 |pmc=7318074 }}</ref>


==Acidic properties==
==Acidic properties==
All three hydrogens are acidic, with dissociation constants p''K''<sub>a1</sub> = 2.14, p''K''<sub>a2</sub> = 7.20, and p''K''<sub>a3</sub> = 12.37.  It follows that, in water solutions, phosphoric acid is mostly dissociated into some combination of its three anions, except at very low [[pH]].
In aqueous solution phosphoric acid behaves as a triprotic acid.
The equilibrium equations are:
:{{chem2|H3PO4 ⇌ H2PO4- + H+}}, p''K''<sub>a1</sub> = 2.14  
:H<sub>3</sub>PO<sub>4</sub> &nbsp;&nbsp;+ H<sub>2</sub>O {{eqm}} H<sub>3</sub>O<sup>+</sup> + H<sub>2</sub>PO<sub>4</sub><sup>−</sup>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; ''K''<sub>a1</sub>= 7.25×10<sup>−3</sup>  [p''K''<sub>a1</sub> = 2.14]
:{{chem2|H2PO4- ⇌ HPO4(2-) + H+}}, p''K''<sub>a2</sub> = 7.20
:H<sub>2</sub>PO<sub>4</sub><sup>−</sup>+ H<sub>2</sub>O {{eqm}} H<sub>3</sub>O<sup>+</sup> + HPO<sub>4</sub><sup>2−</sup> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp; ''K''<sub>a2</sub>= 6.31×10<sup>−8</sup>  [p''K''<sub>a2</sub> = 7.20]
:{{chem2|HPO4(2-) ⇌ PO4(3-) + H+}}, p''K''<sub>a3</sub> = 12.37
:HPO<sub>4</sub><sup>2−</sup>+ H<sub>2</sub>O {{eqm}} H<sub>3</sub>O<sup>+</sup> + &nbsp;PO<sub>4</sub><sup>3−</sup> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; ''K''<sub>a3</sub>= 3.98×10<sup>−13</sup> [p''K''<sub>a3</sub> = 12.37]
The difference between successive p''K'' values is sufficiently large so that salts of either monohydrogen phosphate, {{chem2|HPO4(2-)}} or dihydrogen phosphate, {{chem2|H2PO4-}}, can be prepared from a solution of phosphoric acid by adjusting the pH to be mid-way between the respective p''K'' values.


==Uses==
==Uses==
Line 178: Line 180:
| Soaps and detergents || 1836 || [[Sodium triphosphate|STPP]]
| Soaps and detergents || 1836 || [[Sodium triphosphate|STPP]]
|-
|-
| Food industry || 309 || [[Sodium triphosphate|STPP]] (Na<sub>5</sub>P<sub>3</sub>O<sub>10</sub>), [[Sodium hexametaphosphate|SHMP]], [[Trisodium phosphate|TSP]], [[Disodium pyrophosphate|SAPP]], [[Sodium aluminium phosphate|SAlP]], [[Monocalcium phosphate|MCP]], [[Disodium phosphate|DSP]] (Na<sub>2</sub>HPO<sub>4</sub>), H<sub>3</sub>PO<sub>4</sub>
| Food industry || 309 || [[Sodium triphosphate|STPP]] ({{chem2|Na5P3O10}}), [[Sodium hexametaphosphate|SHMP]], [[Trisodium phosphate|TSP]], [[Disodium pyrophosphate|SAPP]], [[Sodium aluminium phosphate|SAlP]], [[Monocalcium phosphate|MCP]], [[Disodium phosphate|DSP]] ({{chem2|Na2HPO4}}), {{chem2|H3PO4}}
|-
|-
| [[Water treatment]] || 164 || SHMP, [[Sodium triphosphate|STPP]], [[Tetrasodium pyrophosphate|TSPP]], [[Monosodium phosphate|MSP]] (NaH<sub>2</sub>PO<sub>4</sub>), DSP
| [[Water treatment]] || 164 || SHMP, [[Sodium triphosphate|STPP]], [[Tetrasodium pyrophosphate|TSPP]], [[Monosodium phosphate|MSP]] ({{chem2|NaH2PO4}}), DSP
|-
|-
| [[Toothpaste]]s || 68 || [[Dicalcium phosphate|DCP]] (CaHPO<sub>4</sub>), IMP, SMFP
| [[Toothpaste]]s || 68 || [[Dicalcium phosphate|DCP]] ({{chem2|CaHPO4}}), IMP, SMFP
|-
|-
| Other applications || 287 || [[Sodium triphosphate|STPP]] (Na<sub>3</sub>P<sub>3</sub>O<sub>9</sub>), TCP, APP, DAP, [[zinc phosphate]] (Zn<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>), [[aluminium phosphate]] (AlPO<sub>4</sub>, H<sub>3</sub>PO<sub>4</sub>)
| Other applications || 287 || [[Sodium triphosphate|STPP]] ({{chem2|Na3P3O9}}), TCP, APP, DAP, [[zinc phosphate]] ({{chem2|Zn3(PO4)2}}), [[aluminium phosphate]] ({{chem2|AlPO4}}), {{chem2|H3PO4}}
|}
|}


Food-grade phosphoric acid (additive [[E number|E338]]<ref name=fgovuk>{{cite web|url=http://www.food.gov.uk/policy-advice/additivesbranch/enumberlist#h_7|title=Current EU approved additives and their E Numbers|date=14 March 2012|publisher=Foods Standards Agency|access-date=22 July 2012|archive-date=19 July 2013|archive-url=https://www.webcitation.org/6IDaVXq1n?url=http://www.food.gov.uk/policy-advice/additivesbranch/enumberlist#h_7|url-status=live}}</ref>) is used to acidify foods and beverages such as various [[cola]]s and jams, providing a tangy or sour taste. The phosphoric acid also serves as a [[preservative]].<ref>{{Cite web|title=Why is phosphoric acid used in some Coca‑Cola drinks?{{!}} Frequently Asked Questions {{!}} Coca-Cola GB|url=https://www.coca-cola.co.uk/our-business/faqs/why-is-phosphoric-acid-used-in-coca-cola-drinks-diet-coke-coke-zero|access-date=2021-08-31|website=www.coca-cola.co.uk|language=en-GB|archive-date=2 August 2021|archive-url=https://web.archive.org/web/20210802114054/https://www.coca-cola.co.uk/our-business/faqs/why-is-phosphoric-acid-used-in-coca-cola-drinks-diet-coke-coke-zero|url-status=live}}</ref> Soft drinks containing phosphoric acid, which would include [[Coca-Cola]], are sometimes called [[phosphate soda]]s or phosphates. Phosphoric acid in soft drinks has the potential to cause dental erosion.<ref>{{Cite journal|title=Dietary advice in dental practice|journal=British Dental Journal|volume=193|issue=10|pages=563–568|date=23 November 2002|doi=10.1038/sj.bdj.4801628|pmid=12481178|last1=Moynihan|first1=P. J.|doi-access=free}}</ref> Phosphoric acid also has the potential to contribute to the formation of [[Kidney stone disease|kidney stones]], especially in those who have had kidney stones previously.<ref name=Qa2014>{{cite journal |last1= Qaseem |first1= A |last2= Dallas |first2= P |last3= Forciea |first3= MA |last4= Starkey |first4= M |last5= Denberg |first5= TD |display-authors= 4 |title= Dietary and pharmacologic management to prevent recurrent nephrolithiasis in adults: A clinical practice guideline from the American College of Physicians |journal= [[Annals of Internal Medicine]] |date= 4 November 2014 |volume= 161 |issue= 9 |pages= 659–67 |doi= 10.7326/M13-2908 |pmid=25364887|doi-access= free }}</ref>
Food-grade phosphoric acid (additive [[E number|E338]]<ref name=fgovuk>{{cite web|url=http://www.food.gov.uk/policy-advice/additivesbranch/enumberlist#h_7|title=Current EU approved additives and their E Numbers|date=14 March 2012|publisher=Foods Standards Agency|access-date=22 July 2012|archive-date=21 August 2013|archive-url=https://web.archive.org/web/20130821045312/http://food.gov.uk/policy-advice/additivesbranch/enumberlist#h_7|url-status=live}}</ref>) is used to acidify foods and beverages such as various [[cola]]s and jams, providing a tangy or sour taste. The phosphoric acid also serves as a [[preservative]].<ref>{{Cite web|title=Why is phosphoric acid used in some Coca‑Cola drinks?{{!}} Frequently Asked Questions {{!}} Coca-Cola GB|url=https://www.coca-cola.co.uk/our-business/faqs/why-is-phosphoric-acid-used-in-coca-cola-drinks-diet-coke-coke-zero|access-date=2021-08-31|website=www.coca-cola.co.uk|language=en-GB|archive-date=2 August 2021|archive-url=https://web.archive.org/web/20210802114054/https://www.coca-cola.co.uk/our-business/faqs/why-is-phosphoric-acid-used-in-coca-cola-drinks-diet-coke-coke-zero|url-status=live}}</ref> Soft drinks containing phosphoric acid, which would include [[Coca-Cola]], are sometimes called [[phosphate soda]]s or phosphates. Phosphoric acid in soft drinks has the potential to cause dental erosion.<ref>{{Cite journal|title=Dietary advice in dental practice|journal=British Dental Journal|volume=193|issue=10|pages=563–568|date=23 November 2002|doi=10.1038/sj.bdj.4801628|pmid=12481178|last1=Moynihan|first1=P. J.|doi-access=free}}</ref> Phosphoric acid also has the potential to contribute to the formation of [[Kidney stone disease|kidney stones]], especially in those who have had kidney stones previously.<ref name=Qa2014>{{cite journal |last1= Qaseem |first1= A |last2= Dallas |first2= P |last3= Forciea |first3= MA |last4= Starkey |first4= M |last5= Denberg |first5= TD |display-authors= 4 |title= Dietary and pharmacologic management to prevent recurrent nephrolithiasis in adults: A clinical practice guideline from the American College of Physicians |journal= [[Annals of Internal Medicine]] |date= 4 November 2014 |volume= 161 |issue= 9 |pages= 659–67 |doi= 10.7326/M13-2908 |pmid=25364887|doi-access= free }}</ref>


Specific applications of phosphoric acid include:
Specific applications of phosphoric acid include:
* in anti-rust treatment by [[phosphate conversion coating]] or [[Passivation (chemistry)|passivation]]
* in anti-rust treatment by [[phosphate conversion coating]] or [[Passivation (chemistry)|passivation]]
** to prevent [[iron]] [[oxidation]] by means of the [[Parkerization (metallurgy)|Parkerization]] process
* to prevent [[iron]] [[oxidation]] by means of the [[Parkerization (metallurgy)|Parkerization]] process
* as an external standard for [[phosphorus-31 nuclear magnetic resonance]]
* as an external standard for [[phosphorus-31 nuclear magnetic resonance]]
* in [[phosphoric acid fuel cell]]s
* in [[phosphoric acid fuel cell]]s
Line 201: Line 203:


== Safety ==
== Safety ==
Although phosphoric acid is not a [[strong acid]], solutions can irritate the skin and damage the eyes.
A link has been shown between long-term regular cola intake and [[osteoporosis]] in later middle age in women (but not men).<ref>{{cite journal|vauthors=Tucker KL, Morita K, Qiao N, Hannan MT, Cupples LA, Kiel DP | title=Colas, but not other carbonated beverages, are associated with low bone mineral density in older women: The Framingham Osteoporosis Study| journal=American Journal of Clinical Nutrition| volume=84| pages=936–942| issue = 4| date = 1 October 2006| pmid = 17023723 | doi=10.1093/ajcn/84.4.936| doi-access=free}}</ref>
A link has been shown between long-term regular cola intake and [[osteoporosis]] in later middle age in women (but not men).<ref>{{cite journal|vauthors=Tucker KL, Morita K, Qiao N, Hannan MT, Cupples LA, Kiel DP | title=Colas, but not other carbonated beverages, are associated with low bone mineral density in older women: The Framingham Osteoporosis Study| journal=American Journal of Clinical Nutrition| volume=84| pages=936–942| issue = 4| date = 1 October 2006| pmid = 17023723 | doi=10.1093/ajcn/84.4.936| doi-access=free}}</ref>


Revision as of 16:27, 26 June 2022


This article is about orthophosphoric acid. For other acids commonly called "phosphoric acid", see Phosphoric acids and phosphates.
Not to be confused with Phosphorous acid.
Template:Chembox imageTemplate:Chembox imageTemplate:Chembox image sbsTemplate:Chembox imageTemplate:Chembox image sbsTemplate:Chembox imageTemplate:Chembox image sbsTemplate:Chembox AllOtherNamesTemplate:Chembox IdentifiersTemplate:Chembox PropertiesTemplate:Chembox StructureTemplate:Chembox ThermochemistryTemplate:Chembox HazardsTemplate:Chembox Related
Phosphoric acid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Template:Chembox Footer/tracking


Phosphoric acid (orthophosphoric acid, monophosphoric acid or phosphoric(V) acid) is an inorganic compound with the chemical formula H
3PO
4. Phosphoric acid is a colorless solid, it is commonly encountered as an 85% aqueous solution, which is a colourless, odourless, and non-volatile syrupy liquid. It is a major industrial chemical, being a component of many fertilizers.

The compound is an acid. Removal of all three H+
 ions gives the phosphate ion PO3−
4. Removal of one or two protons gives dihydrogen phosphate ion H
2PO−
4, and the hydrogen phosphate ion HPO2−
4, respectively. Phosphoric acid forms esters, called organophosphates.[1]

The name "orthophosphoric acid" can be used to distinguish this specific acid from other "phosphoric acids", such as pyrophosphoric acid. Nevertheless, the term "phosphoric acid" often means this specific compound; and that is the current IUPAC nomenclature.

Production

Phosphoric acid is produced industrially by one of two routes, wet processes and dry.[2]

Wet process

In the wet process, a phosphate-containing mineral such as calcium hydroxyapatite and fluorapatite are treated with sulfuric acid.[3]

Ca
5(PO
4)
3OH + 5 H
2SO
4 → 3 H
3PO
4 + 5 [[CaSO
4]] + H
2O
Ca
5(PO
4)
3F + 5 H
2SO
4 → 3 H
3PO
4 + 5 [[CaSO
4]] + HF

Calcium sulfate (gypsum, CaSO
4) is a by-product, which is removed as phosphogypsum. The hydrogen fluoride (HF) gas is streamed into a wet (water) scrubber producing hydrofluoric acid. In both cases the phosphoric acid solution usually contains 23–33% P2O5 (32–46% H
3PO
4). It may be concentrated to produce commercial- or merchant-grade phosphoric acid, which contains about 54–62% P
2O
5 (75–85% H
3PO
4). Further removal of water yields superphosphoric acid with a P
2O
5 concentration above 70% (corresponding to nearly 100% H
3PO
4). The phosphoric acid from both processes may be further purified by removing compounds of arsenic and other potentially toxic impurities.

Dry process

To produce food-grade phosphoric acid, phosphate ore is first reduced with coke in an electric arc furnace, to give elemental phosphorus. Silica is also added, resulting in the production of calcium silicate slag. Elemental phosphorus is distilled out of the furnace and burned with air to produce high-purity phosphorus pentoxide, which is dissolved in water to make phosphoric acid.[4]

Acidic properties

In aqueous solution phosphoric acid behaves as a triprotic acid.

H
3PO
4 ⇌ H
2PO−
4 + H+
, pKa1 = 2.14
H
2PO−
4 ⇌ HPO2−
4 + H+
, pKa2 = 7.20
HPO2−
4 ⇌ PO3−
4 + H+
, pKa3 = 12.37

The difference between successive pK values is sufficiently large so that salts of either monohydrogen phosphate, HPO2−
4 or dihydrogen phosphate, H
2PO−
4, can be prepared from a solution of phosphoric acid by adjusting the pH to be mid-way between the respective pK values.

Uses

The dominant use of phosphoric acid is for fertilizers, consuming approximately 90% of production.[5]

Application Demand (2006) in thousands of tons Main phosphate derivatives
Soaps and detergents 1836 STPP
Food industry 309 STPP (Na
5P
3O
10), SHMP, TSP, SAPP, SAlP, MCP, DSP (Na
2HPO
4), H
3PO
4
Water treatment 164 SHMP, STPP, TSPP, MSP (NaH
2PO
4), DSP
Toothpastes 68 DCP (CaHPO
4), IMP, SMFP
Other applications 287 STPP (Na
3P
3O
9), TCP, APP, DAP, zinc phosphate (Zn
3(PO
4)
2), aluminium phosphate (AlPO
4), H
3PO
4

Food-grade phosphoric acid (additive E338[6]) is used to acidify foods and beverages such as various colas and jams, providing a tangy or sour taste. The phosphoric acid also serves as a preservative.[7] Soft drinks containing phosphoric acid, which would include Coca-Cola, are sometimes called phosphate sodas or phosphates. Phosphoric acid in soft drinks has the potential to cause dental erosion.[8] Phosphoric acid also has the potential to contribute to the formation of kidney stones, especially in those who have had kidney stones previously.[9]

Specific applications of phosphoric acid include:

Safety

Although phosphoric acid is not a strong acid, solutions can irritate the skin and damage the eyes.

A link has been shown between long-term regular cola intake and osteoporosis in later middle age in women (but not men).[15]

At moderate concentrations phosphoric acid solutions are irritating to the skin. Contact with concentrated solutions can cause severe skin burns and permanent eye damage.[16]

See also

References

  1. ↑ Westheimer, F.H. (6 June 1987). "Why nature chose phosphates". Science. 235 (4793): 1173–1178 (see pp. 1175–1176). Bibcode:1987Sci...235.1173W. CiteSeerX 10.1.1.462.3441. doi:10.1126/science.2434996. PMID 2434996.
  2. ↑ Becker, Pierre (1988). Phosphates and phosphoric acid. New York: Marcel Dekker. ISBN 978-0824717124.
  3. ↑ Template:Greenwood&Earnshaw2nd
  4. ↑ Geeson, Michael B.; Cummins, Christopher C. (2020). "Let's Make White Phosphorus Obsolete". ACS Central Science. 6 (6): 848–860. doi:10.1021/acscentsci.0c00332. PMC 7318074. PMID 32607432.
  5. ↑ Template:Ullmann
  6. ↑ "Current EU approved additives and their E Numbers". Foods Standards Agency. 14 March 2012. Archived from the original on 21 August 2013. Retrieved 22 July 2012.
  7. ↑ "Why is phosphoric acid used in some Coca‑Cola drinks?| Frequently Asked Questions | Coca-Cola GB". www.coca-cola.co.uk. Archived from the original on 2 August 2021. Retrieved 31 August 2021.
  8. ↑ Moynihan, P. J. (23 November 2002). "Dietary advice in dental practice". British Dental Journal. 193 (10): 563–568. doi:10.1038/sj.bdj.4801628. PMID 12481178.
  9. ↑ Qaseem, A; Dallas, P; Forciea, MA; Starkey, M; et al. (4 November 2014). "Dietary and pharmacologic management to prevent recurrent nephrolithiasis in adults: A clinical practice guideline from the American College of Physicians". Annals of Internal Medicine. 161 (9): 659–67. doi:10.7326/M13-2908. PMID 25364887.
  10. ↑ Toles, C.; Rimmer, S.; Hower, J. C. (1996). "Production of activated carbons from a washington lignite using phosphoric acid activation". Carbon. 34 (11): 1419. doi:10.1016/S0008-6223(96)00093-0.
  11. ↑ Wet chemical etching. Archived 25 September 2012 at the Wayback Machine umd.edu.
  12. ↑ Wolf, S.; R. N. Tauber (1986). Silicon processing for the VLSI era: Volume 1 – Process technology. p. 534. ISBN 978-0-9616721-6-4.
  13. ↑ "Ingredient dictionary: P". Cosmetic ingredient dictionary. Paula's Choice. Archived from the original on 18 January 2008. Retrieved 16 November 2007.
  14. ↑ "STAR SAN" (PDF). Five Star Chemicals. Archived (PDF) from the original on 8 February 2016. Retrieved 17 August 2015.
  15. ↑ Tucker KL, Morita K, Qiao N, Hannan MT, Cupples LA, Kiel DP (1 October 2006). "Colas, but not other carbonated beverages, are associated with low bone mineral density in older women: The Framingham Osteoporosis Study". American Journal of Clinical Nutrition. 84 (4): 936–942. doi:10.1093/ajcn/84.4.936. PMID 17023723.
  16. ↑ "Phosphoric Acid, 85 wt.% SDS". Sigma-Aldrich. 5 May 2016. Archived from the original on 18 January 2017. Retrieved 16 January 2017.

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