How can a solution of potassium phosphate be distinguished chemically from a potassium sulfate solution?

1 Answer
Sep 2, 2016

Use the ammonium molybdate test.


Warm each solution with dilute nitric acid; then add a solution of ammonium molybdate.

The solution of potassium sulfate will give no reaction.

The solution of potassium phosphate will give a canary yellow precipitate of ammonium molybdate.

The equation is

#"K"_3"PO"_4"(aq)" + 12underbrace(("NH"_4)_2"MoO"_4"(aq)")_color(red)("ammonium molybdate") + "21HNO"_3"(aq)" → underbrace(("NH"_4)_3"PO"_4·"12MoO"_3"(s)")_color(red)("ammonium phosphomolybdate") + "21NH"_4"NO"_3"(aq)" + "12H"_2"O(l)"#