Hey I have a problem on my hands, I'm trying to find the concentration of ammonium phosphate in mol/L. Equation: Excuse the badly written equation, I'm not quite sure on how to use subscrips/arrow signs on here. (NH4)3P04 --------------- 3NH4 + P04 Known Data: Mass of 3NH4 measured with probe = 400 mg/L (0.40 g) Mass of P04 measured with probe = 10 mg/L (0.01 g) Moles of 3NH4 = 0.0678 moles Moles of P04 = 0.00009915 moles The problem: I have found the mass of each of the products using a probe. The 3:1 ratio is not existent and this is due to a number of reasons (ignore this). How do I determine the mass of the original substance put in. Once I know that I can find the morality quite easily. I've attempted it but my high school teacher said I was wrong. I added the masses and now when I look back, it was a stupid thing to do. I think I need to use the solubility of ammonium phosphate some how, the solubility in water is 58g/100mL Any help would be much appreciated, I really am stuck.