Standard Test Method for Hardness in Water

SCOPE
1.1 This test method covers the determination of hardness in water by titration. This test method is applicable to waters that are clear in appearance and free of chemicals that will complex calcium or magnesium. The lower detection limit of this test method is approximately 2 to 5 mg/L as CaCO3; the upper limit can be extended to all concentrations by sample dilution. It is possible to differentiate between hardness due to calcium ions and that due to magnesium ions by this test method.
1.2 This test method was tested on reagent water only. It is the user's responsibility to ensure the validity of the test method for waters of untested matrices.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

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Publication Date
09-May-2002
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ASTM D1126-96 - Standard Test Method for Hardness in Water
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NOTICE: This standard has either been superseded and replaced by a new version or
withdrawn. Contact ASTM International (www.astm.org) for the latest information.
Designation: D 1126 – 96
AMERICAN SOCIETY FOR TESTING AND MATERIALS
100 Barr Harbor Dr., West Conshohocken, PA 19428
Reprinted from the Annual Book of ASTM Standards. Copyright ASTM
Standard Test Method for
1
Hardness in Water
This standard is issued under the fixed designation D 1126; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense. Consult the DoD Index of Specifications and
Standards for the specific year of issue which has been adopted by the Department of Defense.
3
1. Scope T , which has a red color in the presence of calcium and
magnesium and a blue color when they are sequestered.
1.1 This test method covers the determination of hardness in
water by titration. This test method is applicable to waters that
5. Significance and Use
are clear in appearance and free of chemicals that will complex
5.1 Hardness salts in water, notably calcium and magne-
calcium or magnesium. The lower detection limit of this test
sium, are the primary cause of tube and pipe scaling, which
method is approximately 2 to 5 mg/L as CaCO ; the upper limit
3
frequently causes failures and loss of process efficiency due to
can be extended to all concentrations by sample dilution. It is
clogging or loss of heat transfer, or both.
possible to differentiate between hardness due to calcium ions
5.2 Hardness is caused by any polyvalent cations, but those
and that due to magnesium ions by this test method.
other than Ca and Mg are seldom present in more than trace
1.2 This test method was tested on reagent water only. It is
amounts. The term hardness was originally applied to water in
the user’s responsibility to ensure the validity of the test
which it was hard to wash; it referred to the soap-wasting
method for waters of untested matrices.
properties of water. With most normal alkaline water, these
1.3 This standard does not purport to address all of the
soap-wasting properties are directly related to the calcium and
safety concerns, if any, associated with its use. It is the
magnesium content.
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
6. Interferences
bility of regulatory limitations prior to use.
6.1 The substances shown in Table 1 represent the highest
concentrations that have been found not to interfere with this
2. Referenced Documents
determination.
2.1 ASTM Standards:
6.2 The test method is not suitable for highly colored
2
D 1066 Practice for Sampling Steam
waters, which obscure the color change of the indicator.
2
D 1129 Terminology Relating to Water
2
D 1193 Specification for Reagent Water
7. Reagents
D 3370 Practices for Sampling Water from Closed Con-
7.1 Purity of Reagents—Reagent grade chemicals shall be
2
duits
used in all tests. Unless otherwise indicated, it is intended that
all reagents shall conform to the specifications of the Commit-
3. Terminology
4
tee on Analytical Reagents of the American Chemical Society.
3.1 Definitions:
Other grades may be used, provided it is first ascertained that
3.1.1 equivalent per million (epm)—a unit chemical equiva-
the reagent is of sufficiently high purity to permit its use
lent weight of solute per million unit weights of solution.
without lessening the accuracy of the determination.
3.1.2 For definitions of other terms used in this test method,
7.2 Purity of Water—Unless otherwise indicated, reference
refer to Terminology D 1129.
to water shall be understood to mean reagent water conforming
to Specification D 1193, Type I. Other reagent water types may
4. Summary of Test Method
be used provided it is first ascertained that the water is of
4.1 Calcium and magnesium ions in water are sequestered
sufficiently high purity to permit its use without adversely
by the addition of disodium ethylenediamine tetraacetate. The
end point of the reaction is detected by means of Chrome Black
3
3–Hydroxy–4-(1–hydroxy-2–napththyl) azo-7–nitro–1 naphthalenesulfonic
acid, sodium salt, Color Index 14645.
1 4
This test method is under the jurisdiction of ASTM Committee D-19 on Water Reagent Chemicals, American Chemical Society Specifications, American
and is the direct responsibility of Subcommittee D19.05 on Inorganic Constituents Chemical Society, Washington, DC. For suggestions on the testing of reagents not
in Water. listed by the American Chemical Society, see Analar Standards for Laboratory
Current edition approved Aug. 10, 1996. Published October 1996. Originally Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharm
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