Magnesium Phosphate Formula

Magnesium Phosphate

Magnesium phosphate is a general salt of magnesium and phosphate that are formed in various hydrates as monomagnesium phosphate, dimagnesium phosphate and trimagnesium phosphate. This article mainly deals with the magnesium phosphate formula and the structural magnesium phosphate formula. 


Magnesium phosphate is an inorganic compound that is formed from the electrostatic bond between the electropositive magnesium cation and the electronegative phosphate anion and thus the nature of the bond of magnesium phosphate is purely ionic. It is found to be amorphous in nature and as it forms various magnesium acid salt hydrates of phosphoric acid, thus their water crystallization values differ. Thus the chemical formula of magnesium phosphate is Mg3(PO4)2. The ionic chemical formula of magnesium phosphate is represented as [Mg]2+[PO4]3-.

Magnesium Phosphate Structure

According to the chemical formula of magnesium phosphate which is Mg3(PO4)2 the divalent magnesium ion is in ionic bond through electrostatic force of attraction with the trivalent electronegative phosphate ion and the structure produced is an electrovalent structure of magnesium phosphate. The structural molecular formula of magnesium phosphate is illustrated below. 

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In the molecular formula of magnesium phosphate, magnesium is the only metal whereas sulfur and oxygen are both nonmetals. Thus oxygen and sulfur atoms covalently bond together to make trivalent electronegative sulfate atoms and the two covalently bonded electropositive magnesium atoms form an ionic bond with the three sulfate atoms that are electrostatically attracted to each other. 

The Other Molecular Formula of Magnesium Phosphate Hydrides are:

  1. Monomagnesium Phosphate (H4MgO8P2)

It is a white crystalline solid with no smell and has a molecular weight equals to 218.277 g/mol. It is mostly in powdered form and is soluble in water, therefore, used as an additive. This magnesium and phosphate formula is also known as the magnesium dihydrogen phosphate formula. It is basically the acidic magnesium salt of diphosphoric acid that is synthesised by slowly adding the aqueous dispersion of sodium hydroxide to the phosphoric acid until the phosphorus and the magnesium formula of molar ratio becomes 1:2.  This entire reaction is carried out at 60oC and about 0.1% of hydrogen peroxide is added to the reaction mixture which is then eventually dried and milled. It has a functional use as an acidifier, stabilizer and raising agent. The illustration of the structural formula is as follows:

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  1. Dimagnesium Phosphate (HMgO4P)

It is a white crystalline solid in powdered form with a molar mass equal to 120.283 g/mol. Its density as trihydrate is 2.13 g/cm3. It is also known as the magnesium hydrogen phosphate formula. It is a magnesium salt of phosphoric acid in which magnesium and phosphorus are present in a molar ratio of 1:1 and is dibasic in nature. It is odourless, sparingly soluble in water but highly soluble in dilute acids and insoluble in ethanol. It is a very good dietary supplement that is widely used in many infant formulas as well as athlete supplements. It is considered a nutrient adjunct as well as a nutrient agent. Its structural illustration of the chemical formula is as follows.

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  1. Trimagnesium phosphate (Mg3O8P2)

It is a magnesium acid salt of phosphoric acid and is white crystalline in nature with variable amounts of water of crystallization where X = 0,5,8,22. It has a molar mass equal to 262.855 g / mol and is absolutely insoluble in water but soluble in a salt solution. It has a melting point of 1184oC. It is an octahydrate that is found as a mineral in bobierrite in nature. The magnesium and phosphate of this acidic magnesium salt are in a molar ratio 2:3. The octahydrate form of magnesium salt [Mg(PO4)2] ・8H2O is formed when monomagnesium phosphate in its stoichiometric quantity reacts with magnesium hydroxide. The anhydrous form of the salt is obtained when the octahydrate is heated at 400 oC. The molecular structure of the trimagnesium phosphate is given below.

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FAQs (Frequently Asked Questions)

Q1. What is the Formula Mass of Magnesium Phosphate?

alculated with the help of the magnesium and phosphate ionic formula that goes like [Mg]2+[PO4]3-. Here magnesium belongs to group 2 with a molar mass of 24.31 and it has three atoms present to neutralize the -3 charge of phosphate. Similarly, the molar mass of phosphorus is 30.97 and just one atom of Phosphorus is present and oxygen has a molar mass of 16 with 4 oxygen atoms present. This way just as magnesium ion, the entire phosphate group having its 2 atoms in the molecule to neutralize the +2 charge on magnesium. Therefore the formula becomes

[24.31 x 3] + [ 30.97 + (16 x2)] x 2 = 262.87 g/mol

Q2. What is the Magnesium Ammonium Phosphate Formula?

Ans.  Magnesium ammonium phosphate is also known as struvite which is a phosphate mineral with a molecular formula NH4MgPO4・6H2O. It is basically a white to a yellowish or brownish-white pyramidal crystal that is in platey mica like form and possesses an orthorhombic system. It is a very soft mineral with a very little hardness that varies between 1.5 to 2 on the Mohs scale and has a low specific gravity of 1.7. It is sparingly soluble in neutral and alkaline solution but is readily soluble in acidic solutions. It is also very popular as kidney stones that are in crystal form in the urine of animals and humans if their system is infected with ammonia producing organisms. 

Q3. State the Difference Between Molar Mass and Molecular Mass.

Ans. molecular mass is the mass of the molecule that is present in a substance that consists of the atomic mass of the summation of all the atoms with the no. of similar atoms present together to form that particular molecule but the molar mass is a mass of one mole of a substance. It is just a number that is equivalent to 6.023 x 10-23 molecules as per Avogadro’s number. It means that one mole of CO2 will contain 6.023 x 10-23 molecules of CO2.