The phosphate ions of a solution react with ammonium molybda

The phosphate ions of a solution react with ammonium molybdate to give ammonium phosphomolybdate which is then reduced by aminonaptholsulfonic acid (ANSA) to form a blue complex. The chemistry is complicated, but the reaction (not balanced) is: . Ammonium molybdate + phosphate ammonium phosphomolybdate + ANSA Blue Complex (NH)2Mo0 PO (NH4)3[POdMoO3)121 H2NCIoH5(OH)SOJH Blue Complex

Solution

Its not a complete reaction because in the preparation of ammonium phosphomolybdate we react ammonium molybdate with nitric acid and phosphoric acid. So the reaction is

12(NH₄)₂MoO₄ + H₃PO₄ + 21HNO₃ ----------------> (NH₄)₃ [PO₄(MoO₃)₁₂ ] + 21 NH₄NO₃ + 12 H₂O

This ammonium phosphomolybedate is insoluble in nitric acid so we can easily collect it and then do reaction with ANSA so that blue colored complex is formed.