Chemistry - Salt Analysis Question with Solution | TestHub

The addition of excess concentrated HNO₃ is crucial for two reasons: it converts molybdate ions (${Mo{O}_4}^{2-}$ ) into reactive molybdic acid ($H_{2}Mo{O}_4$), which is essential for the formation of the phosphomolybdate complex. Additionally, the high acidity suppresses the ionization of phosphoric acid ($H_{3}P{O}_4$), ensuring it exists predominantly in its undissociated form, which is necessary for the reaction. This also prevents the precipitation of other metal molybdates.