Monopotassium phosphate (MKP) (also, potassium dihydrogenphosphate, KDP, or monobasic potassium phosphate) is the
inorganic compound
In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemist ...
with the formula KH
2PO
4. Together with
dipotassium phosphate
Dipotassium phosphate (K2HPO4) (also dipotassium hydrogen orthophosphate; potassium phosphate dibasic) is the inorganic compound with the formula K2HPO4.(H2O)x (x = 0, 3, 6). Together with monopotassium phosphate (KH2PO4.(H2O)x), it is often used ...
(K
2HPO
4.(H
2O)
x) it is often used as a
fertilizer
A fertilizer (American English) or fertiliser (British English; see spelling differences) is any material of natural or synthetic origin that is applied to soil or to plant tissues to supply plant nutrients. Fertilizers may be distinct from ...
,
food additive, and
buffering agent
A buffer solution (more precisely, pH buffer or hydrogen ion buffer) is an aqueous solution consisting of a mixture of a weak acid and its conjugate base, or vice versa. Its pH changes very little when a small amount of strong acid or base is ...
. The salt often cocrystallizes with the dipotassium salt as well as with
phosphoric acid
Phosphoric acid (orthophosphoric acid, monophosphoric acid or phosphoric(V) acid) is a colorless, odorless phosphorus-containing solid, and inorganic compound with the chemical formula . It is commonly encountered as an 85% aqueous solution, w ...
.
Single crystal
In materials science, a single crystal (or single-crystal solid or monocrystalline solid) is a material in which the crystal lattice of the entire sample is continuous and unbroken to the edges of the sample, with no grain boundaries.RIWD. "Re ...
s are
paraelectric at room temperature. At temperatures below , they become
ferroelectric
Ferroelectricity is a characteristic of certain materials that have a spontaneous electric polarization that can be reversed by the application of an external electric field. All ferroelectrics are also piezoelectric and pyroelectric, with the ad ...
.
Structure
Monopotassium phosphate can exist in several
polymorphs. At room temperature it forms
paraelectric crystals with tetragonal symmetry. Upon cooling to it transforms to a
ferroelectric
Ferroelectricity is a characteristic of certain materials that have a spontaneous electric polarization that can be reversed by the application of an external electric field. All ferroelectrics are also piezoelectric and pyroelectric, with the ad ...
phase of orthorhombic symmetry, and the transition temperature shifts up to when hydrogen is replaced by deuterium.
[ Heating to changes its structure to monoclinic.][ When heated further, MKP decomposes, by loss of water, to potassium metaphosphate, , at .
]
Manufacturing
Monopotassium phosphate is produced by the action of phosphoric acid
Phosphoric acid (orthophosphoric acid, monophosphoric acid or phosphoric(V) acid) is a colorless, odorless phosphorus-containing solid, and inorganic compound with the chemical formula . It is commonly encountered as an 85% aqueous solution, w ...
on potassium carbonate
Potassium carbonate is the inorganic compound with the formula K2 CO3. It is a white salt, which is soluble in water. It is deliquescent, often appearing as a damp or wet solid. Potassium carbonate is mainly used in the production of soap and gl ...
.
Applications
Fertilizer-grade MKP powder contains the equivalent of 52% and 34% , and is labeled NPK
Many countries have standardized the labeling of fertilizers to indicate their contents of major nutrients. The most common labeling convention, the NPK or N-P-K label, shows the amounts of the chemical elements nitrogen, phosphorus, and potas ...
0-52-34. MKP powder is often used as a nutrient
A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi, and protists. Nutrients can be incorporated into cells for metabolic purposes or excret ...
source in the greenhouse
A greenhouse (also called a glasshouse, or, if with sufficient heating, a hothouse) is a structure with walls and roof made chiefly of Transparent ceramics, transparent material, such as glass, in which plants requiring regulated climatic condit ...
trade and in hydroponics
Hydroponics is a type of horticulture and a subset of hydroculture which involves growing plants, usually crops or medicinal plants, without soil, by using water-based mineral nutrient solutions in aqueous solvents. Terrestrial or aquatic plan ...
.
As a crystal
A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macro ...
, MKP is noted for its non-linear optical properties. Used in optical modulator
An optical modulator is a device which is used to modulate a beam of light. The beam may be carried over free space, or propagated through an optical waveguide (optical fibre). Depending on the parameter of a light beam which is manipulated, modul ...
s and for non-linear optics
Nonlinear optics (NLO) is the branch of optics that describes the behaviour of light in ''nonlinear media'', that is, media in which the polarization density P responds non-linearly to the electric field E of the light. The non-linearity is typica ...
such as second-harmonic generation
Second-harmonic generation (SHG, also called frequency doubling) is a nonlinear optical process in which two photons with the same frequency interact with a nonlinear material, are "combined", and generate a new photon with twice the energy o ...
(SHG).
Also to be noted is KD*P, potassium dideuterium phosphate, with slightly different properties. Highly deuterated
Isotopic labeling (or isotopic labelling) is a technique used to track the passage of an isotope (an atom with a detectable variation in neutron count) through a reaction, metabolic pathway, or cell. The reactant is 'labeled' by replacing specific ...
KDP is used in nonlinear frequency conversion of laser light instead of protonated (regular) KDP due to the fact that the replacement of protons with deuterons in the crystal shifts the third overtone of the strong OH molecular stretch to longer wavelengths, moving it mostly out of the range of the fundamental line at approximately 1064 nm of neodymium-based lasers. Regular KDP has absorbances at this wavelength of approximately 4.7–6.3% per cm of thickness while highly deuterated KDP has absorbances of typically less than 0.8% per cm.
Monopotassium phosphate is used as an ingredient in sports drink
Sports drinks, also known as electrolyte drinks, are functional beverages whose stated purpose is to help Sportsperson, athletes replace water, electrolytes, and energy before, during and especially after training or competition. There are many ...
s such as Gatorade
Gatorade is an American brand of sports-themed beverage and food products, built around its signature line of sports drinks. Gatorade is currently manufactured by PepsiCo and is distributed in over 80 countries. The beverage was first develop ...
and Powerade
Powerade is a sports drink created, manufactured and marketed by The Coca-Cola Company. Its primary competitor is Gatorade, owned by PepsiCo.
History
In 1988, Powerade became the official sports drink of the Olympics, alongside Aquarius, ano ...
.
In medicine, monopotassium phosphate is used for phosphate substitution in hypophosphatemia
Hypophosphatemia is an electrolyte disorder in which there is a low level of phosphate in the blood. Symptoms may include weakness, trouble breathing, and loss of appetite. Complications may include seizures, coma, rhabdomyolysis, or softening ...
.
Gallery
Image:KDP crystal.jpg, A large KDP crystal, used in the form of slices at the National Ignition Facility
The National Ignition Facility (NIF) is a laser-based inertial confinement fusion (ICF) research device, located at Lawrence Livermore National Laboratory in Livermore, California, United States. NIF's mission is to achieve fusion ignition w ...
Image:Monocristal dsc03676.jpg, Alternate angle, covered
References
External links
International Chemical Safety Card 1608
EPA: Potassium dihydrogen phosphate Fact Sheet
{{Potassium compounds
Second-harmonic generation
Phosphates
Potassium compounds
Acid salts
Nonlinear optical materials
Transparent materials
E-number additives
Inorganic fertilizers