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.
In this tutorial we first discuss about identifying phosphate ion (PO43-). Next we study some compounds and reactions of phosphorus and acids of phosphorus.
Phosphate minerals include calcium phosphate (Ca3(PO4)2) , apatite(Ca5(PO42)3OH), fluoroapatite (Ca5(PO4)3F) and chloroapatite (Ca5(PO4)3Cl)
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.
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.
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).
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-.
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.
Magnesia is a mixture of of MgCl2 with NH4OH and NH4Cl. It gives a white crystalline precipitate of MgNH4PO4.
CrPO4 is a greenish precipitate.
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.
Now, we discuss about some phosphorus compounds and their reactions/
H3PO4, H3PO3, H3PO2, H4P2O7 are oxyacids of phosphorus.
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.
There are three salts of Na as NaH2PO4, Na2HPO4, Na3PO4,
P4O6 + H2O → 4H3PO3
PCl3 + 3H2O → H3PO3 + 3HCl
H3PO3 is a weak acid and a dibasic acid. Oxidation number of P in H3PO3 is +3.
H3PO2 is a weak acid and a monobasic acid. Oxidation number of P in H3PO3 is +3. H3PO2 is an oxidizing acid.
silver phosphate - Ag3PO4