Overview
ISO 910:1977 specifies a titrimetric method for determining the total acidity of industrial sulphuric acid and for calculating the free sulphur trioxide (SO3) content of oleum. The method covers two concentration ranges: sulphuric acid at or below 98% (m/m) and sulphuric acid above 98% (m/m) (oleum). The procedure is based on oxidation of the sample with hydrogen peroxide followed by titration of total acidity with standard volumetric sodium hydroxide in the presence of methyl red indicator.
Key topics and technical requirements
- Scope: Two cases - H2SO4 ≤ 98% (m/m) and H2SO4 > 98% (m/m, oleum).
- Principle: Oxidize the sample with H2O2, then titrate the total acidity with 1 N NaOH using methyl red as end‑point indicator.
- Reagents specified:
- Hydrogen peroxide, 60 g/L (neutral to methyl red)
- Sodium hydroxide, 1 N standard volumetric solution
- Methyl red solution (1 g/L in 95% ethanol)
- Apparatus: Ordinary laboratory glassware including burette (±0.05 mL), 500 mL conical flask with ground glass stopper, and a small spherical glass ampoule for handling oleum test portions.
- Procedure highlights:
- For ≤98% H2SO4: weigh ~2 g sample, oxidize with 5 mL H2O2, titrate after dilution.
- For >98% (oleum): prepare test portion in sealed ampoule, break into cold water, dilute to mark, take aliquot for titration.
- Calculations:
- Total acidity (as % H2SO4) is calculated from titrant volume, sample mass and conversion factor (1 mL of exactly 1 N NaOH corresponds to 0.04904 g H2SO4).
- Convert total acidity to SO3 using factor 0.8162 (B = A × 0.8162).
- Determine water combined as H2SO4 and sulphuric acid content per the standard, then compute free SO3 for oleum (expressed as % by mass).
- Reporting: Include method reference, results and units, any unusual observations, and any non‑standard operations.
Applications and users
- Quality control laboratories in chemical plants producing or handling sulphuric acid and oleum.
- Analytical and process laboratories in fertilizers, mineral processing, petroleum refining and sulfate‑based chemical manufacturing.
- Purchasing and inspection teams who need validated methods for verifying total acidity, purity and free SO3 content.
- Environmental and compliance labs that monitor acidic streams where accurate acid quantification is required.
Related standards
ISO 910 is part of a suite of ISO methods for sulphuric acid and oleum. Related standards include:
- ISO 911 - Evaluation of sulphuric acid concentration by density
- ISO 912 / ISO 3423 - Determination of sulphur dioxide (various methods)
- ISO 913–914, ISO/R 915, and others for ash, total nitrogen, iron, lead, chlorides and trace contaminants in sulphuric acid
Keywords: ISO 910, sulphuric acid, oleum, total acidity, titrimetric method, free sulphur trioxide, titration, methyl red, hydrogen peroxide, sodium hydroxide, industrial acid analysis.