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