Monopotassium Phosphate

What is The Formula of Monopotassium Phosphate?

Monopotassium Phosphate is nothing but the monopotassium salt of phosphoric acid bearing the formula KH2PO4

Monopotassium Phosphate is easily soluble in water and insoluble in ethanol. It is commercially available. Monopotassium Phosphate produces ceramics of high quality at the time of its reaction with MgO. The reaction between the chloride or potassium carbonate and the phosphate generally produce the above-mentioned compound. In the reaction, phosphate is released in pure form as a crystalline material. The industrial preparation of Monopotassium Phosphate involves adding of 1 mol of a water solution of potassium hydroxide to 1 mol of phosphoric acid. 

What is Monopotassium Phosphate?

Monopotassium Phosphate is one of the most important inorganic compounds. The main utilization of this compound is as fertilizer, food additive and buffering agent. Sometimes the salt co-crystalizes with the dipotassium salt as well with the phosphoric acid. IUPAC names of Monopotassium Phosphate are Potassium dihydrogen phosphate and Potassium dihydrogen (tetraoxidophosphate) (1- ). The systematic IUPAC name of Monopotassium Phosphate is Potassium dihyroxidophosphate (1-). Other names of the compound are Potassium phosphate monobasic, Phosphoric acid, monopotassium salt and Potassium biphosphate.

What is The Structure of Monopotassium Phosphate?

There is a huge possibility of the existence of Monopotassium Phosphate in several polymorphs. Paraelectric crystals with tetragonal symmetry are formed by the compound at room temperature. If cooling is done up to -150 degree C (-238 degree F) it converts to a ferroelectric phase of orthorhombic symmetry. If hydrogen is replaced by deuterium then the transition temperature shifts up to -50 degree C (-58 degree F). The structure of the Monopotassium Phosphate is changed to monoclinic if the substance is heated up to 190 degree Celcius (374 degree F). If the heat is increased further then Monopotassium Phosphate decomposes because of the loss of water and turns into potassium metaphosphate (KPO3) at 400 degree Celcius (752 degree F). The complete structure of the Monopotassium Phosphate is given in the following table for the convenience of the students.

Structure of The Monopotassium Phosphate


Name of the space group


Symbol bearing Pearson

a (mm)

b (mm)

c (mm)


Density in g/cm3

Temperature (C, F K) 










< -150 deg C

    -238 deg F

      123 K











-150 to 190 deg C, -238 to 374 deg F, 123 to 463K


P2 1/c







190 to 400 deg C, 374 to 752 deg F, 463 to 673K

What Are The Properties of Monopotassium Phosphate?

The physical properties, as well as chemical properties of Monopotassium Phosphate, are given in the following. 

Physical Properties:

The physical properties of Monopotassium Phosphate are as follows:

  • Monopotassium Phosphate is odourless.

  • The physical appearance of the compound is a white powder which is deliquescent. 

  • The covalently bonded unit of the compound is 2.

  • Heavy atom count of Monopotassium Phosphate is 6.

  • Complexity of the compound is 61.2.

  • Monopotassium Phosphate is freely soluble in water.

Chemical Properties:

The chemical properties of Monopotassium Phosphate are as follows:

  • After dissolving in the water Monopotassium Phosphate forms phosphoric acid and potassium hydroxide. The chemical equation of the above phenomenon is as follows:

KH2PO4 + H2O 🡪 H3PO4 + KOH

  • Disodium phosphate, water and potassium hydroxide are formed by the reaction between Monopotassium Phosphate and base. The chemical formula of the above reaction is as follows:

KH2PO4 + 2NaOH 🡪 H2O + KOH + Na2HPO4

How Monopotassium Phosphate is synthesized?

The reaction of phosphoric acid on potassium carbonate produces Monopotassium Phosphate. 

What are the uses of Monopotassium Phosphate?

Approximately 52% of P2O5 and 34% of K2O are contained in fertilizer grade Monopotassium Phosphate powder. The fertilizer grade Monopotassium Phosphate is symbolised as NPL 0-52-34. There is a remarkable application of Monopotassium Phosphate in the greenhouse trade and in hydroponics as a nutrient. 

Monopotassium Phosphate is vastly used as a crystal for its non-linear optical properties. The powder form of the compound applied in optical modulators and for non-linear optics like a second harmonic generation. 

A modified form of Monopotassium Phosphate is termed as potassium di-deuterium phosphate (KD2PO4). Non-linear frequency conversion of laser light is done by highly deuterated KDP in place of protonated (regular) KDP because the replacement of protons with deuterons in the crystal shifts the third overtone of the strong OH molecular stretch to longer wavelengths, moving it maximum out of the range of the basic line at apparently 1064 mm of neodymium- based lasers. Regular KDP has the absorbance power at this particular wavelength of near about 4.7- 6.3% per cm of thickness at the time when highly deuterated KDP has an absorbance of typically less than 0.8% per cm.

Another notable utilization of Monopotassium Phosphate is as an ingredient in sports drinks like Gatorade and Powerade. 

Monopotassium Phosphate is used in the preparation of sodium phosphates, ammonium phosphates, calcium phosphates and other phosphates. The compound is also used in eggs, low sodium products, meat products and milk products for colour preservation. 

What are the hazards of Monopotassium Phosphate?

Monopotassium Phosphate is regarded as a mildly hazardous substance. It may cause skin, eye and respiratory tract irritation. The eye is the most possible area of contact with Monopotassium Phosphate and it causes acute eye irritation. If there is prolonged contact with the skin then skin irritation may occur. There is a possibility of upper respiratory tract irritation caused by Monopotassium Phosphate. Intake of a large quantity of Monopotassium Phosphate will cause irritation, nausea, vomiting, diarrhoea, abnormal cramps etc. 

How Monopotassium Phosphate is identified?

Monopotassium Phosphate can be identified by the following phenomenons:

  • CAS number of Monopotassium Phosphate is 7778-77-0.

  • 3D model of the compound appears as an interactive image.

  • ChEMBL of Monopotassium Phosphate is ChEMBL 1200925.

  • ECHA InfoCard is 100.029.012.

  • EC Number of Monopotassium Phosphate is 231-913-4.

  • E Number of the compound is E340 (I).

  • RTECS Number of Monopotassium Phosphate is TC6615500.

Monopotassium Phosphate is one of the most vastly used compounds in the agricultural industry. Though there are few hazards in utilizing this compound it is treated as one of the best fertilizers for the plant health. Since it is freely soluble in water it is very easy to use in the field. The hazards can be avoided by taking some preliminary and basic protections. Since there are not too many hazardous components present in the compound there is very much less chance of side effect for its use. Monopotassium Phosphate is commercially available at a very cheap rate and the farmers can buy this for agriculture.

FAQ (Frequently Asked Questions)

1. Why Monopotassium Phosphate is a great option for plant health?

The strong roots of plants are made by the eco-friendly fertilizer Monopotassium Phosphate when the plants require it most. If the compound is used at the beginning of the season then it will help in establishing firm roots early in the growing season to ensure that the crops are full and healthy. Monopotassium Phosphate consists of 52% phosphorous and 34% potassium and is a very efficient and useful form of fertilizer that feeds the plants with the nutrition they need to thrive in any crop condition. Monopotassium Phosphate is also a very useful resource of nutrition for sugar-rich foods like fruits with increased sugar content leading to a fresh, ripe and delicious harvest.

2. Why do crops require Phosphorous?

Phosphorous is the main component which helps in controlling the protein synthesis in plants leading to healthy development, cell division and ultimate growth of the plant. New plant tissues are formed by the phosphorous and when the extra quantities are added to the soil, root growth escalates, establishing the resistance power of the plant in the changing weather conditions. 

Disaster can happen to the crops if there is a dearth of Phosphorous. Fertilizing leads to the best production. Adequate quantity of Monopotassium Phosphate must be applied to the plants to make the harvest season fascinating.  The deficiency of phosphorous may lead to the appearance of Anthocyanin pigments which turns the sugar-rich plants from red to purple.

3. Why do crops require Potassium?

Monopotassium Phosphate is a widely used fertilizer because it contains potassium also. The plants get healthy if an adequate amount of Potassium is applied to the plants. Potassium is absorbed by the plants in large quantity. Hence, the Potassium levels are kept steady by the use of Monopotassium Phosphate. Potassium regulates the enzyme activity in the plants. Potassium also helps the plants in respiration, transpiration and plants are made capable of absorbing other vital nutrients. Potassium also plays a crucial role in the transportation of water and nutrients through the xylem of the plant. A satisfactory quantity of potassium increases the root growth and helps stop the growth and spread of crop diseases. 

4. What is Phosphoric acid?

Phosphoric acid is composed of four atoms of oxygen, one atom of phosphorous and three atoms of hydrogen. The other name of the compound is phosphoric (V) acid or orthophosphoric acid. The presence of the acid can be seen in teeth and bones and it helps in the metabolic process.