Monocalcium phosphate

Monocalcium phosphate
Names
IUPAC name
Calcium 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
7758-23-8 Yes
PubChem 24454
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
Solubility soluble in HCl, nitric acid, acetic acid
1.5176
Structure
Crystal structure triclinic
Hazards
EU Index Not listed
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 1: Exposure would cause irritation but only minor residual injury. E.g., turpentine Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special 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 noted otherwise, data is 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 ("ACMP" or "CMP-A" for anhydrous monocalcium phosphate). It is commonly found as the monohydrate (""MCP" or "MCP-M"), Ca(H2PO4)2·H2O (CAS# 10031-30-8). 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 tends 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. 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. Residual HF typically reacts with silicate minerals co-mingled with the phophate ores to produce hydrofluorosilicic 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 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 Klaus Schrödter, Gerhard Bettermann, Thomas Staffel, Friedrich Wahl, Thomas Klein, Thomas Hofmann "Phosphoric Acid and Phosphates" in Ullmann’s Encyclopedia of Industrial Chemistry 2008, Wiley-VCH, Weinheim. doi:10.1002/14356007.a19_465.pub3
  2. ↑ Gunnar Kongshaug et al. "Phosphate Fertilizers" in Ullmann's Encyclopedia of Industrial Chemistry, 2002, Wiley-VCH, Weinheim. 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