Calcium dihydrogen phosphate
Acid calcium phosphate
Calcium acid phosphate
Monobasic calcium phosphate
Phosphoric acid, calcium salt (2:1)
3D model (JSmol)
|Molar mass||234.05 g/mol|
|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|
Refractive index (nD)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|what is ?)(|
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. Both salts are colourless solids. They are used mainly as superphosphate fertilizers and are also popular leavening agents.
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
Use in fertilizers
- 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 phosphate ores to produce hydrofluorosilicic acid (H2SiF6). The majority of the hexafluorosilicic acid is converted to aluminium fluoride and cryolite for the processing of aluminium. These materials are central to the conversion of aluminium ore into aluminium metal.
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).
- 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
- Gunnar Kongshaug et al. "Phosphate Fertilizers" in Ullmann's Encyclopedia of Industrial Chemistry, 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a19_421.pub2
- 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