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