ASTM D1126-02(2007)e1
(Test Method)Standard Test Method for Hardness in Water
Standard Test Method for Hardness in Water
SIGNIFICANCE AND USE
Hardness salts in water, notably calcium and magnesium, are the primary cause of tube and pipe scaling, which frequently causes failures and loss of process efficiency due to clogging or loss of heat transfer, or both.
Hardness is caused by any polyvalent cations, but those other than Ca and Mg are seldom present in more than trace amounts. The term hardness was originally applied to water in which it was hard to wash; it referred to the soap-wasting properties of water. With most normal alkaline water, these soap-wasting properties are directly related to the calcium and magnesium content.
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.
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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Designation: D1126 − 02 (Reapproved 2007)
StandardTest Method for
Hardness in Water
This standard is issued under the fixed designation D1126; 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 (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
´ NOTE—Added acronym to 3.1.2 and updated 11.5 editorially in August 2007.
1. Scope 3.1.1 equivalent per million (epm), n—a unit chemical
equivalent weight of solute per million unit weights of solu-
1.1 Thistestmethodcoversthedeterminationofhardnessin
tion.
water by titration. This test method is applicable to waters that
3.1.2 laboratory control sample (LCS), n—a solution with
are clear in appearance and free of chemicals that will complex
certified hardness.
calcium or magnesium. The lower detection limit of this test
methodisapproximately2to5mg/LasCaCO ;theupperlimit
3 3.1.3 For definitions of other terms used in this test method,
can be extended to all concentrations by sample dilution. It is
refer to Terminology D1129.
possible to differentiate between hardness due to calcium ions
and that due to magnesium ions by this test method.
4. Summary of Test Method
1.2 This test method was tested on reagent water only. It is
4.1 Calcium and magnesium ions in water are sequestered
the user’s responsibility to ensure the validity of the test
by the addition of disodium ethylenediamine tetraacetate. The
method for waters of untested matrices.
endpointofthereactionisdetectedbymeansofChromeBlack
T , which has a red color in the presence of calcium and
1.3 This standard does not purport to address all of the
magnesium and a blue color when they are sequestered.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro-
5. Significance and Use
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use. 5.1 Hardness salts in water, notably calcium and
magnesium, are the primary cause of tube and pipe scaling,
2. Referenced Documents
which frequently causes failures and loss of process efficiency
2.1 ASTM Standards: due to clogging or loss of heat transfer, or both.
D1066 Practice for Sampling Steam
5.2 Hardness is caused by any polyvalent cations, but those
D1129 Terminology Relating to Water
other than Ca and Mg are seldom present in more than trace
D1193 Specification for Reagent Water
amounts. The term hardness was originally applied to water in
D2777 Practice for Determination of Precision and Bias of
which it was hard to wash; it referred to the soap-wasting
Applicable Test Methods of Committee D19 on Water
properties of water. With most normal alkaline water, these
D3370 Practices for Sampling Water from Closed Conduits
soap-wasting properties are directly related to the calcium and
D5847 Practice for Writing Quality Control Specifications
magnesium content.
for Standard Test Methods for Water Analysis
6. Interferences
3. Terminology
6.1 The substances shown in Table 1 represent the highest
3.1 Definitions:
concentrations that have been found not to interfere with this
determination.
This test method is under the jurisdiction of ASTM Committee D19 on Water
6.2 The test method is not suitable for highly colored
and is the direct responsibility of Subcommittee D19.05 on Inorganic Constituents
in Water.
waters, which obscure the color change of the indicator.
Current edition approved Aug. 1, 2007. Published August 2007. Originally
approved in 1950. Last previous edition approved in 2002 as D1126 – 02. DOI:
7. Reagents
10.1520/D1126-02R07E01.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on 3–Hydroxy–4-(1–hydroxy-2–napththyl) azo-7–nitro–1 naphthalenesulfonic
the ASTM website. acid, sodium salt, Color Index 14645.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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D1126 − 02 (Reapproved 2007)
TABLE 1 Freedom of Reaction from Interferences
7.3 Ammonium Hydroxide Solution(1+4)—Mix 1 volume
Maximum Maximum of NH OH (sp gr 0.90) with 4 volumes of water.
Concentration Concentration
7.4 Buffer Solution—Prepare the buffer solution in three
Without Without
Substance Interference Interference
steps as follows:
in the Total in the Calcium
7.4.1 Dissolve 40 g of sodium tetraborate
Hardness Hardness
(Na B O ·10H O) in 800 mL of water.
Test, mg/L Test, mg/L
2 4 7 2
7.4.2 Dissolve 10 g of sodium hydroxide (NaOH), 10 g of
+++
Aluminum, Al 20 5
sodium sulfide (Na S·9H O), and 10 g of potassium sodium
+ A
2 2
Ammonium, NH 2 000
−
tartrate (KNaC O ·4H O) in 100 mL of water.
Bicarbonate, HCO . 500
3 4 6 2
Bromine, Br . 2
7.4.3 When cool mix the two solutions and add1gof
++
Cadmium, Cd 20 .
magnesium disodium ethylenediamine tetraacetate, having a
−−
Carbonate, CO 1 000 50
−
Chloride, Cl 10 000 . magnesium-to-EDTAmole ratio of 1 to 1. Make up to 1 Lwith
Chlorine, Cl . 2
water. Keep the solution bottle stoppered when not in use. The
−−
Chromate, CrO 500 500
++ reagent will be effective for at least 1 month.
Cobalt, Co 0.3 .
++
Copper, Cu 20 2
7.5 Calcium Solution, Standard (1 mL = 0.20 mg CaCO )—
+++ B 3
Iron, ferric, Fe 10 20
++ B Dissolve0.2000gofCaCO in3to5mLofHCl(1 + 4).Dilute
Iron, ferrous, Fe 10 20 3
++
Lead, Pb 20 5
to 1 L with water.
++ C C
Manganese, Mn 1 10
++ D
7.6 Calcium Indicator—Use powdered hydroxynaphthol
Nickel, Ni 0.5 .
−
Nitrate, NO 500 500
blue, or grind solid hydroxynaphthol blue to 40 to 50 mesh
−
Nitrite, NO 500 500
size.
−−−
Phosphate, PO 100 .
−−
Silicate, SiO 200 100
7.7 Hardness Indicator—The hardness indicator can be
++ EE
Strontium, Sr
−− prepared, stored, and used in liquid or powder form.
Sulfate, SO 10 000 10 000
−−
Sulfite, SO 500 500
7.7.1 Hardness Indicator Solution—Dissolve 0.5 g of
Tannin, Quebracho 200 50
Chrome Black T in 50 mL of diethanolamine or trietha-
+ +++
Tin, stannic, Sn 10 5
++
nolamine. Store the solution in a dark-colored bottle. This
Tin, stannous, Sn 10 5
++
Zinc, Zn 20 5
solution has a storage life of several months.
A
No data are available. 7.7.2 Hardness Indicator Powder—Grind 0.5 g of Chrome
B
Iron will not interfere in concentrations up to 200 mg/L. However, the red color
Black T with 100 g of powdered sodium chloride. Use a
of the end point may return in about 30 s.
C dark-colored bottle for storage. The powder has a storage life
Manganese will not interfere in concentrations up to 10 mg/L if a few crystals
of K Fe(CN) ·3H O are added to the buffer immediately before use. of at least 1 year.
4 6 2
D
Accurate results can be obtained in the presence of 1 mg/L nickel, but the end
7.8 Hydrochloric Acid (1+4)—Mix 1 volume of concen-
point is slow under these conditions.
E
If strontium is present, it will be titrated with calcium and magnesium.
trated hydrochloric acid (sp gr 1.19) with 4 volumes of water.
7.9 Disodium Ethylenediamine Tetraacetate (Na H EDTA)
2 2
Solution, Standard (1 mL = 1.0 mg CaCO )—Dissolve 3.8 g of
disodium ethylenediamine tetraacetate dihydrate in approxi-
7.1 Purity of Reagents—Reagent grade chemicals shall be
mately 800 mL of water.Adjust the pH of the solution to 10.5
used in all tests. Unless otherwise indicated, it is intended that
with NaOH solution (50 g/L). Determine the concentration of
all reagents shall conform to the specifications of the Commit-
this solution using the standard calcium solution, and that
tee onAnalytical Reagents of theAmerican Chemical Society.
procedure in Section 9 that will be used for the sample analysis
Other grades may be used, provided it is first ascertained that
(9.1, 9.2,or 9.3).Adjust the concentration of the EDTAso that
the reagent is of sufficiently high purity to permit its use
1mLwillbeequivalentto1.0mgofCaCO .Storethestandard
without lessening the accuracy of the determination.
EDTA in
...
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