Question

You mix 50 mL of 0.1 M ammonium phosphate with 75 mL of 0.05 M calcium nitrate. How much of a precipitate forms from this reaction (in grams)?

Answer 1

2(NH4)3PO4 + 3Ca(NO3)2 ==> Ca3(PO4)2 + 6NH4NO3

moles (NH4)3PO4 = M x L
moles Ca(NO3)2 = M x L.

Using the coefficients in the balanced equation, convert moles (NH4)3PO4 to moles Ca3(PO4)2.
Same procedure, convert moles Ca(NO3)2 to moles Ca3(PO4)2.
In limiting reagent problems, the answers do NOT agree; therefore, one of them must be wrong. In limiting reagent problems, the correct value is ALWAYS the smaller value and the reagent producing that value is the limiting reagent.

Using the smaller value, convert moles to grams. g = moles x molar mass.