When anhydrous liquid ammonia reacts with orthophosphoric acid (H3PO4), which fertiliser product is formed?

Introduction / Context:
Neutralisation of phosphoric acid with ammonia is a core route to produce NP fertilisers. Depending on the ammonia-to-acid ratio, monoammonium phosphate (MAP) or diammonium phosphate (DAP) is obtained, both collectively termed ammonium phosphate fertilisers.

Given Data / Assumptions:

• Reactants: anhydrous NH3 and H3PO4 (orthophosphoric acid).
• Reaction carried out under standard fertiliser plant conditions (scrubber/neutraliser or pipe reactor).

Concept / Approach:
NH3 neutralises acidic protons on H3PO4 to form ammonium phosphate salts. A 1:1 NH3:H3PO4 basis forms MAP (NH4H2PO4), while higher NH3 produces DAP ((NH4)2HPO4). “Superphosphate” and “triple superphosphate” are produced instead by reacting phosphate rock with sulphuric or phosphoric acid, not with ammonia directly.

Step-by-Step Solution:

Verification / Alternative check:
Process flow diagrams for NP plants show ammonia neutralisers producing MAP/DAP slurry that is granulated and dried, confirming the product identity.

Why Other Options Are Wrong:

• Superphosphate and triple superphosphate: manufactured by acidulating phosphate rock, not by reacting NH3 with H3PO4.
• Potassium nitrate: unrelated salt from KNO3 processes.
• None of these: incorrect because ammonium phosphate is formed.

Common Pitfalls:
Confusing NP neutralisation chemistry with superphosphate route; these are distinct process lines in phosphate fertiliser plants.

Final Answer:
ammonium phosphate