Superphosphate manufacture: Reaction of which mineral acid with phosphate rock yields superphosphate fertilizers?

Introduction / Context:Superphosphate fertilizers are produced by acidulating phosphate rock (apatite). The classical “single superphosphate” (SSP) route uses sulphuric acid, resulting in monocalcium phosphate along with gypsum as a by-product. Distinguishing this from the phosphoric-acid route for triple superphosphate (TSP) is a common exam checkpoint.

Given Data / Assumptions:

• “Superphosphate” generally refers to SSP unless otherwise specified as TSP.
• Feedstock is rock phosphate rich in apatite minerals.
• We are to identify the acid reagent used in the standard SSP process.

Concept / Approach:In SSP manufacture, phosphate rock reacts with sulphuric acid to form monocalcium phosphate in an acidic slurry while precipitating calcium sulphate (gypsum). The cured product contains water-soluble phosphate suitable for direct application. In contrast, TSP is made by reacting rock phosphate with phosphoric acid, giving a higher analysis product; thus “sulphuric acid” aligns specifically with superphosphate in the classical sense.

Step-by-Step Solution:Identify the named product: superphosphate typically implies SSP.Recall the reagent: sulphuric acid is used to acidulate rock in SSP.Select “Sulphuric acid” from the list.

Verification / Alternative check:Fertilizer process references list SSP as rock phosphate + H2SO4 → monocalcium phosphate + gypsum; TSP is separately produced via phosphoric acid.

Why Other Options Are Wrong:Hydrochloric or nitric acid routes are niche and not the standard for superphosphate; phosphoric acid corresponds to TSP, not SSP; acetic acid is irrelevant to industrial phosphate fertilizer production.

Common Pitfalls:Confusing the generic term “superphosphate” with “triple superphosphate.” Unless “triple” is specified, the safe exam assumption is SSP with sulphuric acid.

Final Answer:Sulphuric acid