Industrial nitric acid by the Ostwald process The oxidation of ammonia followed by absorption of nitrogen oxides in water produces commercial nitric acid of approximately what concentration (weight % HNO3)?

Introduction / Context:
The Ostwald process converts ammonia to nitric acid via catalytic oxidation to NO/NO2 and subsequent absorption in water. A common exam point is the typical product strength obtained directly from absorption without further concentration steps.

Given Data / Assumptions:

• Feed: anhydrous NH3 and air; Pt-Rh catalyst for oxidation.
• Absorber: countercurrent water contacting NOx to form HNO3.
• No secondary concentration by dehydration or extractive methods considered.

Concept / Approach:
Direct absorption yields a nitric acid solution limited by vapor–liquid equilibrium and heat effects, typically around 55–68 wt%. Plants often report about 60–62 wt% HNO3 as the standard “weak acid” strength, which can later be concentrated (e.g., by azeotropic distillation or extractive techniques) to stronger grades if needed.

Step-by-Step Solution:

Verification / Alternative check:
Process design references list weak nitric acid near 60 wt% from absorption, with higher strengths requiring energy-intensive concentration and water removal.

Why Other Options Are Wrong:

• 30%: Too dilute for standard Ostwald absorption performance.
• 95% or 100%: These are fuming/super-azeotropic or anhydrous strengths not obtained by simple absorption.

Common Pitfalls:
Confusing “weak acid” from the absorber with “concentrated nitric acid” supplied for nitration; the latter needs additional unit operations.

Final Answer:
60