Chemistry:Monocalcium phosphate

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Monocalcium phosphate
Calcium dihydrogen phosphate.png
Monocalcium phosphate spoon.JPG
Names
IUPAC name
Calcium bis(dihydrogen phosphate)
Other names
Acid calcium phosphate
Calcium acid phosphate
Calcium diorthophosphate
Calcium biphosphate
Calcium superphosphate
Monobasic calcium phosphate
Monocalcium orthophosphate
Phosphoric acid, calcium salt (2:1)
Identifiers
3D model (JSmol)
ChemSpider
UNII
Properties
CaH4P2O8
Molar mass 234.05 g/mol
Appearance White powder
Density 2.220 g/cm3
Melting point 109 °C (228 °F; 382 K)
Boiling point 203 °C (397 °F; 476 K) (decomposes)
2 g/100 mL
1.5176
Structure
Triclinic
Hazards
NFPA 704 (fire diamond)
Flammability code 0: Will not burn. E.g. waterHealth code 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no codeNFPA 704 four-colored diamond
0
1
0
Flash point Non-flammable
Related compounds
Other anions
 Calcium pyrophosphate
Other cations
 Magnesium phosphate
Dicalcium phosphate
Tricalcium phosphate
Strontium phosphate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Monocalcium phosphate is an inorganic compound with the chemical formula Ca(H2PO4)2 ("AMCP" or "CMP-A" for anhydrous monocalcium phosphate). It is commonly found as the monohydrate ("MCP" or "MCP-M"), Ca(H2PO4)2·H2O. Both salts are colourless solids. They are used mainly as superphosphate fertilizers and are also popular leavening agents.[1]

Preparation

Material of relatively high purity, as required for baking, is produced by treating calcium hydroxide with phosphoric acid:

Ca(OH)2 + 2 H3PO4 → Ca(H2PO4)2 + 2 H2O

Samples of Ca(H2PO4)2 tend to convert to dicalcium phosphate:

Ca(H2PO4)2 → Ca(HPO4) + H3PO4

Applications

Use in fertilizers

Superphosphate fertilizers are produced by treatment of "phosphate rock" with acids ("acidulation"). Using phosphoric acid, fluorapatite is converted to Ca(H2PO4)2:

Ca5(PO4)3F + 7 H3PO4 → 5 Ca(H2PO4)2 + HF

This solid is called triple superphosphate. Several million tons are produced annually for use as fertilizers. Using sulfuric acid, fluorapatite is converted to a mixture of Ca(H2PO4)2 and CaSO4. This solid is called single superphosphate.

Residual HF typically reacts with silicate minerals co-mingled with the phosphate ores to produce hexafluorosilicic acid (H2SiF6). The majority of the hexafluorosilicic acid is converted to aluminium fluoride and cryolite for the processing of aluminium.[1] These materials are central to the conversion of aluminium ore into aluminium metal.

When sulfuric acid is used, the product contains phosphogypsum (CaSO4·2H2O) and is called single superphosphate. [2]

Use as leavening agent

Calcium dihydrogen phosphate is used in the food industry as a leavening agent, i.e., to cause baked goods to rise. Because it is acidic, when combined with an alkali carbonate ingredient, commonly sodium bicarbonate (baking soda) or potassium bicarbonate, it reacts to produce carbon dioxide and a salt. Outward pressure of the carbon dioxide gas causes the rising effect. When combined in a ready-made baking powder, the acid and alkali ingredients are included in the right proportions such that they will exactly neutralize each other and not significantly affect the overall pH of the product. AMCP and MCP are fast acting, releasing most carbon dioxide within minutes of mixing. It is popularly used in pancake mixes. In double-acting baking powders, MCP is often combined with the slow-acting acid sodium acid pyrophosphate (SAPP).[3]

See also

References

  1. ↑ 1.0 1.1 Schrödter, Klaus; Bettermann, Gerhard; Staffel, Thomas; Wahl, Friedrich; Klein, Thomas; Hofmann, Thomas (2008). "Ullmann's Encyclopedia of Industrial Chemistry". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a19_465.pub3. 
  2. ↑ Kongshaug, Gunnar; Brentnall, Bernard A.; Chaney, Keith; Gregersen, Jan-Helge; Stokka, Per; Persson, Bjørn; Kolmeijer, Nick W.; Conradsen, Arne et al. (2014). "Ullmann's Encyclopedia of Industrial Chemistry". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. pp. 1–49. doi:10.1002/14356007.a19_421.pub2. 
  3. ↑ John Brodie, John Godber "Bakery Processes, Chemical Leavening Agents" in Kirk-Othmer Encyclopedia of Chemical Technology 2001, John Wiley & Sons. doi:10.1002/0471238961.0308051303082114.a01.pub2

Further reading

  • Havlin, J.L., J.D. Beaton, S.L. Tisdale, and W.L. Nelson. 2005. Soil Fertility and Fertilizers. 7th edn. Pearson Prentice Hall, N.J., ISBN:0130278246



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