Overview
ISO 979:1974 specifies a standardized method of assay for sodium hydroxide (NaOH) used in industrial applications. This international standard details the titrimetric procedure to determine the alkalinity content of sodium hydroxide expressed as percentages by mass. The standard covers the determination of:
- Total alkalinity, representing all alkaline substances present expressed as NaOH equivalent.
- Caustic alkalinity, which accounts only for the alkali corresponding to NaOH after subtracting alkalinity due to carbonates.
The assay method is based on titration with a standard hydrochloric acid solution, using methyl orange as an indicator. The mass of carbon dioxide (from carbonates) is measured as per ISO 3196. ISO 979:1974 is a technical revision of the previous ISO Recommendation R 979-1969 and has also received approval from IUPAC.
Key Topics
- Scope of Application: Suitable for industrial sodium hydroxide, with assay results expressed as percentages by mass.
- Titration Principle: Utilizes volumetric titration of the total alkalinity with standard hydrochloric acid in the presence of methyl orange indicator.
- Total Alkalinity Calculation: Based on volume of hydrochloric acid consumed during titration.
- Caustic Alkalinity Determination: Deducts carbonate alkalinity (measured via ISO 3196) from total alkalinity for accurate NaOH content.
- Reagents and Apparatus:
- Standard volumetric hydrochloric acid solution.
- Methyl orange indicator.
- Pipettes and burettes with specified accuracy.
- Precision: Titrations are conducted with laboratory-grade equipment ensuring accuracy within defined limits.
- Test Reporting: Includes method reference, numerical results with expression format, any unusual observations, and optional additional analyses.
Applications
ISO 979:1974 is essential for:
- Quality control in manufacturing and industrial processing where sodium hydroxide is used.
- Chemical analysis laboratories requiring standardized assay methods to ensure purity and concentration consistency of NaOH solutions.
- Process monitoring in industries such as pulp and paper, textiles, water treatment, and chemical production where caustic soda’s strength directly impacts product quality.
- Regulatory compliance to verify sodium hydroxide meets industrial standards.
- Research and development activities involving alkaline solutions.
The clarity and repeatability of this method provide reliable data for sodium hydroxide concentration to optimize industrial processes and ensure safety.
Related Standards
- ISO 3195: Sampling and preparation of sodium hydroxide solutions for analysis.
- ISO 3196: Determination of carbonates content in sodium hydroxide by titrimetric method-used in conjunction for calculating caustic alkalinity.
- ISO/R 648 and ISO/R 385: Specifications for laboratory volumetric apparatus ensuring precision in titration.
By aligning with these standards, organizations can ensure comprehensive and consistent analysis procedures for sodium hydroxide used in industrial applications.
Keywords: ISO 979, sodium hydroxide assay, industrial NaOH, method of assay, titration method, total alkalinity, caustic alkalinity, methyl orange indicator, hydrochloric acid titration, sodium hydroxide quality control, chemical analysis of NaOH.