posted by AJ .
If you were given an unknown solution, write the steps that would be needed to prove that a solution contained phosphate.
This really is too general (too open ended). If the solution may contain any anion, one must assure that arsenate and arsenite are not present, then test with ammonium molybdate. If arsenate or arsenite are present, arsenate must be reduced with sodium sulfite, then pptd as As2S3 with H2S. After the excess H2S gas is expelled, perform the ammonium molybdate test.