Solve Equilibrium Problem with Ammonium Phosphate

[Grove1996]

Problem:

I've been working on my assignment and the purpose of it is to determine the concentration of a contaminant present in a sample of water. I've discovered the contaminant is ammonium phosphate with the levels of each being 200% higher than normal water. I obtained these results using an ion-selective electrode and a colorimeter.

Probe Results:
Ammonium: 407.14 mg/L
Phosphate: 9.42 mg/L

I have to determine the amount of ammonium phosphate originally put into the sample of water, and its concentration (molarity). Usually I would do an "ICE" table but I don't know how much ammonium phosphate has originally been put in. I've done the stoichometry and determined that the 3:1 ratio between ammonium and phosphate does not exist (as the probe results suggest). Regardless, I have to determine the amount originally put in (preferably in grams) and the molarity of the solution.

I have no idea where to start, as I said before I would usually do an ICE table but that will not work in this case.

TLDR:

Probe readings show a total of approximately 407 mg/L of ammonium and 9.5 mg/L of phosphate. What process would I do in order to determine the original amount put in, and the molarity of the concentration.

Any help would be much appreciated.

 

[hyddro]

how did you come to the conclusion that it is ammonium phosphate? Not challenging you, but your answer my help me understand your procedure better and potentially help you.