USGS-NWQL: I-1338: Hardness in water by colorimetric titration
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Official Method Name
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Hardness in water by colorimetric titration |
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Current Revision
| 1985 |
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Media
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WATER |
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Instrumentation
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Titration |
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Method Subcategory
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Inorganic |
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Method Source
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Citation
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Methods for the Determination of Inorganic Substances in Water and Fluvial Sediments, Techniques of Water-Resources Investigations of the United States Geological Survey, Book 5, Chapter A1 Edited by Marvin J. Fishman and Linda C. Friedman |
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Brief Method Summary
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Disodium dihydrogen ethylenediamine-tetraacetate (Na2EDTA) forms a slightly ionized, colorless, stable complex with alkaline earth ions. The indicator Eriochrome Black T is bright blue in the absence of alkaline earths, but with them forms a deep-red complex that has a higher ionization constant than that of the Na2EDTA complex. Hence, with Eriochrome Black T as an indicator, the alkaline earth can be titrated with Na2EDTA. All alkaline earth titrate approximately stoichiometrically. The titration should proceed immediately upon addition of the indicator, because the color of the solution fades after standing. The optimum pH of the titration is 10.4 or above. Additional information on the principle of the determination is given by Goetz and others (1950), and by Botha and Webb (1952). |
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Scope and Application
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This procedure is applicable to most natural and treated water, but the method fails conspicuously at times with acidic or polluted water that contains excessive amounts of heavy metals. |
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Applicable Concentration Range
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None given. |
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Interferences
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(1) Acidic or polluted water that contains excessive amounts of heavy metals. (2) Manganese in higher oxidation states than Mn(II). (3) High aluminum concentrations. |
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Quality Control Requirements
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Not Included |
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Sample Handling
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Container Description: 125 mL polyethylene bottle. Treatment and Handling: Use unfiltered sample to rinse bottle. Max holding time: 180 days. |
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Maximum Holding Time
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180 days |
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Relative Cost
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Less than $50 |
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Sample Preparation Methods
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