Single superphosphate assay:\nApproximately what percentage of P2O5 does commercial single superphosphate (SSP) contain?

Introduction / Context:
Fertiliser grades are commonly expressed in terms of oxide equivalents for phosphorus and potassium. Single superphosphate (SSP) is the product of acidulating phosphate rock with dilute sulphuric acid, yielding monocalcium phosphate plus gypsum. Recognizing its typical P2O5 assay is a basic agronomic and process-knowledge checkpoint.

Given Data / Assumptions:

• SSP is a “single” superphosphate, not triple (TSP).
• Commercial grades vary slightly by moisture and production route.
• We use nominal textbook values.

Concept / Approach:
Typical SSP contains roughly 16% P2O5 (often cited as 16–18% P2O5), along with significant calcium sulphate (gypsum) as a matrix. TSP, by contrast, is around 44–46% P2O5 because it is produced by reacting rock phosphate with phosphoric acid rather than sulphuric acid, concentrating the plant-available phosphate fraction. Therefore, the closest range given for SSP is 15–20% P2O5.

Step-by-Step Solution:

Verification / Alternative check:
Manufacturers’ datasheets and fertiliser manuals list SSP grades near 16% P2O5, sometimes slightly higher depending on quality control and granulation.

Why Other Options Are Wrong:

• 30–35% and 65–70% and 85–90%: far too high for SSP; the 44–46% region corresponds to TSP, not SSP.
• 5–10% is below typical commercial specification.

Common Pitfalls:
Confusing SSP and TSP assays; assuming all “superphosphates” have similar P2O5 content.

Final Answer:
15–20%