Manufacture of ordinary superphosphate (OSP): Superphosphate fertilizer is produced industrially by reacting phosphate rock (fluorapatite) with which reagent?

Introduction / Context:Ordinary superphosphate (OSP) is a widely used phosphorus fertilizer made by acidulating phosphate rock to form water-soluble calcium dihydrogen phosphate. Identifying the correct acid is fundamental to understanding fertilizer manufacturing routes and plant design.

Given Data / Assumptions:

• Feed: phosphate rock (largely fluorapatite, Ca10(PO4)6F2).
• Target product: monocalcium phosphate with gypsum byproduct.
• Single-acid process for OSP (not triple superphosphate).

Concept / Approach:In the OSP process, phosphate rock reacts with sulphuric acid to form monocalcium phosphate monohydrate (water-soluble P) and calcium sulphate (gypsum). For triple superphosphate, phosphoric acid is used instead. Organic acids like acetic acid are too weak and impractical; Lewis acids such as AlCl3 are not used for this purpose.

Step-by-Step Solution:Balanced overall reaction (idealized): Ca3(PO4)2 + 2 H2SO4 + 4 H2O → Ca(H2PO4)2·H2O + 2 CaSO4·2H2O.Sulphuric acid provides the sulfate and protons required to convert rock phosphate to soluble mono-calcium phosphate.Therefore, choose 'Sulphuric acid'.

Verification / Alternative check:Industrial practice distinguishes OSP (H2SO4 route) from triple superphosphate (H3PO4 route), confirming the correct acid here.

Why Other Options Are Wrong:Acetic acid cannot effectively convert apatite; AlCl3 is irrelevant; 'None of these' is false because the correct reagent is listed.

Common Pitfalls:

• Confusing OSP with TSP and selecting phosphoric acid; OSP specifically uses sulphuric acid.
• Overlooking gypsum handling as a major byproduct management issue.

Final Answer:Sulphuric acid