Potassium dihydrogen phosphate

Monopotassium phosphate

Two unit cells of MKP viewed close to the b axis
Names
IUPAC names Potassium dihydrogenphosphate Potassium dihydrogen(tetraoxidophosphate)(1−)
Systematic IUPAC name Potassium dihydroxidodioxidophosphate(1−)
Other names Potassium phosphate monobasic; Phosphoric acid, monopotassium salt; potassium biphosphate
Identifiers
CAS Number	7778-77-0 Y
3D model (JSmol)	Interactive image
ChemSpider	22914 N
ECHA InfoCard	100.029.012
EC Number	231-913-4
PubChem CID	516951
RTECS number	TC6615500
UNII	4J9FJ0HL51 Y
InChI InChI=1S/3K.H3O4P/c;;;1-5(2,3)4/h;;;(H3,1,2,3,4)/q3*+1;/p-3 Y Key: LWIHDJKSTIGBAC-UHFFFAOYSA-K Y InChI=1/3K.H3O4P/c;;;1-5(2,3)4/h;;;(H3,1,2,3,4)/q3*+1;/p-3 Key: LWIHDJKSTIGBAC-DFZHHIFOAX
SMILES [K+].OP(O)([O-])=O
Properties
Chemical formula	KH2PO4
Molar mass	136.086 g/mol
Appearance	White powder deliquescent
Odor	odorless pH-??
Density	2.338 g/cm3
Melting point	252.6 °C (486.7 °F; 525.8 K)
Boiling point	400 °C (752 °F; 673 K) (decomposes)
Solubility in water	22.6 g/100 mL (20 °C) 83.5 g/100 mL (90 °C)
Solubility	slightly soluble in ethanol
Acidity (pKa)	6.86
Basicity (pKb)	11.9
Refractive index (nD)	1.4864
Structure
Crystal structure	tetragonal
Space group	I42d
Lattice constant	a = 0.744 nm, b = 0.744 nm, c = 0.697 nm
Hazards
Safety data sheet	External MSDS
NFPA 704	0 1 0
Flash point	Non-flammable
Lethal dose or concentration (LD, LC):
LD50 (median dose)	3200 mg/kg (rat, oral)
Related compounds
Other cations	Monosodium phosphate Monoammonium phosphate
Related compounds	Dipotassium phosphate Tripotassium phosphate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YN ?)
Infobox references

pH-??

Monopotassium phosphate, MKP, (also potassium dihydrogenphosphate, KDP, or monobasic potassium phosphate), KH₂PO₄, is a soluble salt of potassium and the dihydrogen phosphate ion which is used as a fertilizer, a food additive and a fungicide. It is a source of phosphorus and potassium. It is also a buffering agent. When used in fertilizer mixtures with urea and ammonium phosphates, it minimizes escape of ammonia by keeping the pH at a relatively low level.

Single crystals are paraelectric at room temperature. At temperatures below −150 °C (−238 °F) they become ferroelectric.

Monopotassium phosphate can exist in several polymorphs. At room temperature it forms paraelectric crystals with tetragonal symmetry. Upon cooling to −150 °C it transforms to a ferroelectric phase of orthorhombic symmetry, and the transition temperature shifts up to −50 °C to when hydrogen is replaced by deuterium. Heating to 190 °C changes its structure to monoclinic. When heated further, MKP decomposes, by loss of water, to potassium metaphosphate, KPO₃, at 400 °C (752 °F).

Monopotassium phosphate is produced by the action of phosphoric acid on potassium carbonate.

Fertilizer-grade MKP powder contains the equivalent of 52% P₂O₅ and 34% K₂O, and is labeled NPK 0-52-34. MKP powder is often used as a nutrient source in the greenhouse trade and in hydroponics.