Phosphate ion, phosphoric acid occurrence, compounds, identification, reactions

The main source of phosphorous is apatite. Phosphoric acid (H3PO4) is a weak acid. In many occasions phosphate ion give coloured precipitates. Phosphate ions are very important in fertilizing industry.

Molecule of phosphate ion(PO43-)

Molecule of phosphate ion

In this tutorial we first discuss about identifying phosphate ion (PO43-). Next we study some compounds and reactions of phosphorus and acids of phosphorus.

Occurrence of phosphate ion

Phosphate minerals include calcium phosphate (Ca3(PO4)2) , apatite(Ca5(PO42)3OH), fluoroapatite (Ca5(PO4)3F) and chloroapatite (Ca5(PO4)3Cl)

Identify phosphate ion - Qualitative analysis/

Concentrated nitric acid and ammonium molybdate

ammonium molybdate test for identifying phosphate ion

Add concentrated nitric acid (HNO3) to PO43- solution. Next add excess ammonium molybdate (NH4)2MoO4 You can see a yellow precipitate forms. That yellow precipitate will dissolve in ammonia solution.

ammonium molybdate experiment to test to identify phosphate ion

Silver nitrate and phosphate ion solution.

Silver nitrate and phosphate ion solution react and form silver phosphate ( Ag3PO4 ) a yellow precipitate. That precipitate dissolve in dilute nitric acid HNO3 or ammonia solutions.

silver nitrate and phosphate ion solution

Barium chloride and phosphate ion

Barium chloride ( BaCl2 ) aqueous solution and PO43- aqueous solution react and give Ba3(PO4)2, a white precipitate which dissolve in dilute hydrochloric acid(HCl).

Barium chloride  and phosphate ion

BaCl2 and Na2HPO4 reaction

BaCl2 reacts with Na2HPO4 solution to give white precipitate of BaHPO4. which is soluble in acids (except H2SO4).

In the presence of alkaline or NH4OH the HPO43- ion is converted to PO43-.

BaCl2 and Na2HPO4 reaction

Ferric chloride and phosphate ion

Ferric chloride ( FeCl3 ) and PO43- react and give ferric phosphate(FePO4) a yellow precipitate. This yellow precipitate will dissolve in dilute nitric acid. But do not dissolve in acetic (CH3COOH) acid.

Ferric chloride and phosphate ion

With Magnesia mixture

Magnesia is a mixture of of MgCl2 with NH4OH and NH4Cl. It gives a white crystalline precipitate of MgNH4PO4.

Magnesia mixture and phosphate ion reaction

CrPO4 is a greenish precipitate.

Fertilizer Production and phosphate ion

Naturally occurring calcium phosphate(Ca3(PO4)2) is the primary resource utilized in producing fertilizer. But Ca3(PO4)2 is insoluble in water. Because PO43- ion is basic, it reacts with an acid to produce H2PO4- and it gives Ca(H2PO4)2 is more soluble than Ca3(PO4)2. Sulfuric acid is used as the acid.

Fertilizer-Production and calcium phosphate solubility

Now, we discuss about some phosphorus compounds and their reactions/

Oxyacids of phosphorus

H3PO4, H3PO3, H3PO2, H4P2O7 are oxyacids of phosphorus.

Phosphoric(V) acid (H3PO4)

Phosphoric acid is one of the chemicals produced in enormous(very large quantity) quantities, and it is used in many industrial processes. H3PO4 is not a oxidizing acid and a weak acid.

Molecule of Phosphoric acid

There are three salts of Na as NaH2PO4, Na2HPO4, Na3PO4,

Phosphoric acid preparing

P4O6 and water reaction.

P4O6 + H2O → 4H3PO3

PCl3 hydrolysis

PCl3 + 3H2O → H3PO3 + 3HCl

Phosphoric(III) acid (H3PO3)

H3PO3 is a weak acid and a dibasic acid. Oxidation number of P in H3PO3 is +3.

Phosphoric(III) acid

Phosphoric(I) acid (H3PO2)

H3PO2 is a weak acid and a monobasic acid. Oxidation number of P in H3PO3 is +3. H3PO2 is an oxidizing acid.

Phosphoric(I) acid


What are the yellow precipitates of phosphate ion?

silver phosphate - Ag3PO4