Potassium dihydrogen phosphate

May 13, 2024
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Potassium dihydrogen phosphate (KH2PO4) is an inorganic salt with multiple uses. It is also known as monopotassium phosphate, potassium phosphate monobasic, potassium biphosphate, and potassium acid phosphate.

In (1887), Carl. V. Petraeus of Camden, NJ, described a process for making potassium phosphates, specifically KH2PO4 with a slight excess of potassium. His starting materials were 鈥渂one, bone-black, South Carolina rock, or any compounds mainly composed of lime鈥�. Petraeus鈥檚 somewhat convoluted process consisted of five steps:

  1. decomposing the starting material with sulfuric or oxalic acid;
  2. leaching with water to produce an impure 鈥渁cid phosphate of lime鈥� (calcium dihydrogen phosphate);
  3. treating the calcium dihydrogen phosphate with potassium sulfate;
  4. adding sufficient potassium carbonate or hydroxide to form a solution of KH2PO4 with excess potassium; and
  5. after filtering to remove the calcium salts, evaporating the solution to the point of crystallization.

Today, KH2PO4 is manufactured simply via the reaction between widely available phosphoric acid and potassium carbonate.

The uses of KH2PO4 include agricultural plant nutrients, buffering agents in pharmaceuticals and other preparations, and applications that take advantage of its nonlinear optical properties. To that end, in 2006 Changshui Fang and colleagues at Shandong University (Jinan, China) reviewed how and suggested ways to improve the crystals鈥� optical properties.

Large-aperture crystals are useful in , in which an external electric field is used to control the cell鈥檚 refractive index, and in frequency-doubling devices used in .

Potassium dihydrogen phosphate hazard information

Hazard class*GHS code and hazard statement
Not a hazardous substance or mixture

*Globally Harmonized System (GHS) of Classification and Labeling of Chemicals.

Molecule in the News

Dichlromethane1 (methylene chloride, CH2Cl2), the Molecule of the Week for March 4, 2019, is a widely used solvent that has come under increasing pressure from health and environmental regulatory agencies in the past several years.

In the latest move this April, the US Environmental Protection Agency proposed a for all consumer and most industrial and commercial uses, including adhesives, paint strippers, and degreasers. Dichloromethane is the second chemical to be reviewed under the 2016 revision of the Toxic Substances Control Act. The first was asbestos2, and the third is expected to be tetrachloroethylene3.

1. CAS Reg. No. 75-09-2.
2. CAS Reg. No. 1332-21-4.
3. CAS Reg. No. 127-18-4.

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Potassium dihydrogen phosphate听fast facts

CAS Reg. No.7778-77-0
SciFindern namePhosphoric acid, potassium salt (1:1)
Empirical formulaH2O4KP
Molar mass136.09 g/mol
AppearanceColorless crystals or white powder
Melting point253 掳C
Water solubility226 g/L (20 掳C)
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