ISO 2174:1990

Overview

ISO 2174:1990 - "Surface active agents - Preparation of water with known calcium hardness" specifies a laboratory method to prepare and verify aqueous solutions of defined calcium hardness for testing surfactants and related products. The standard describes making a concentrated stock solution from calcium chloride, determining its calcium content by complexometric titration with EDTA, and preparing working waters of required hardness by dilution.

Key Topics

• Purpose: Provide reproducible water of known calcium hardness (expressed in mmol/l) for surfactant testing.
• Units and conversions: Uses mmol/l for hardness (1 mmol/l Ca2+ = 40.08 mg Ca2+/L); Annex A gives conversion factors to other hardness units.
• Reagents:
  • Calcium chloride dihydrate (CaCl2·2H2O) stock preparation (example: 220.5 g dissolved to 5 L to produce ≈300 mmol Ca2+/L).
  • Standardized disodium EDTA solution (c = 0.05 mol/L) for titration.
  • Mixed indicator (Mordant Black 11/C.I. 14645 blended with methyl red and Mg‑EDTA) and ammoniacal solution (note: contains cyanide in the procedure - see safety).
• Analytical method:
  • Determine calcium concentration of the stock by complexometric titration of an aliquot with EDTA until the mixed indicator changes color (red → green).
  • Calculate stock concentration from titrant volume and EDTA concentration; then compute required stock volume for specified hardness and dilute to volume.
• Apparatus: Class A volumetric flasks, pipettes, burette, 5 L glass bottle, conical flasks and analytical balance (standards referenced for glassware and laboratory water).

Applications and Who Uses It

• Laboratories performing surfactant performance and stability tests where water hardness affects foam, detergency, and product behavior.
• Chemical and consumer product manufacturers needing standardized test waters for QA, R&D, method validation, and inter-laboratory comparison.
• Test houses and standards organizations that require reproducible water hardness preparation for protocols involving surface active agents.

Practical benefits: reproducible test waters, clear calculation and dilution steps, and traceable EDTA titration to quantify calcium content before use.

Related Standards

• ISO 3696 - Laboratory water quality
• ISO 385-1 - Burettes
• ISO 1042 - Volumetric flasks
• ISO 648 - Pipettes
• ISO 1773 - Conical flasks and flasks

Note: follow laboratory safety precautions (especially when preparing ammoniacal cyanide-containing reagents) and use the standard for exact formulas, equations and procedural details.