Wet-process phosphoric acid strength: Approximately what percentage (by mass) of P2O5 does typical wet-process phosphoric acid contain?

Introduction / Context:
Wet-process phosphoric acid is produced by digesting phosphate rock with sulfuric acid. The resulting acid strength is commonly expressed as percent P2O5, a conventional industry metric. Knowing the typical concentration is essential for downstream uses like manufacture of triple superphosphate, nitrophosphate, and numerous NPK fertilizers.

Given Data / Assumptions:

• Process: sulfuric acid attack on phosphate rock followed by filtration of gypsum.
• We refer to the typical, commercial wet acid product before further concentration.
• Concentration is expressed as percent P2O5 equivalent.

Concept / Approach:
Standard wet-process acid streams usually fall around 26–32% P2O5, often rounded to “about 30% P2O5.” This strength balances filtration performance, corrosion, and energy costs. Stronger acid can be produced by evaporative concentration, but the base wet acid commonly referenced in fertilizer technology texts is near 30% P2O5.

Step-by-Step Solution:
Recall wet-process acid typical range ≈ 26–32% P2O5.Identify the nearest option representing the conventional value.Select “30.”Note: higher strengths (40+% P2O5) require additional concentration steps.

Verification / Alternative check:
Plant data sheets and fertilizer handbooks frequently cite base wet acid near 28–30% P2O5 before concentrators or hemihydrate processes are applied.

Why Other Options Are Wrong:
10: too dilute for standard trade acid.50 or 70: represent concentrated or merchant-grade acid after additional evaporation, not the base wet-process output.

Common Pitfalls:
Mixing P2O5 percentages with H3PO4 wt%—they are related but not numerically identical; always check the basis used in a question.

Final Answer:
30