The moles of ammonia that are needed to react completely with 3 moles of phosphoric acid is 6 moles
Step-by-step explanation
Step 1:
write the a balanced chemical reaction that occur between ammonia and phosphoric acid.
3NH3 + H3PO4 → (NH4)3PO4
Step 2: use of mole ratio of NH3 :H3PO4 to calculate moles of NH3
that is, NH3: H3PO4 is 3:1 therefore the moles of NH3 = 3moles x 3/1 = 9 moles
3 moles of NH3 was in excess therefore the mole of NH3 that reacted = 9-3 = 6 moles