Standard Test Method for Acidity in Basic Chromium Tanning Liquors

SIGNIFICANCE AND USE
The acidity of a chrome tanning liquor, as determined by this test method, is rarely employed as such. This result is normally combined with the results of a chromium analysis (see Test Method D 3898) to determine a property of the liquor called basicity. This property, equal to the percentage by which anions in a normal chromic salt have been replaced by hydroxyl in the solution being analyzed, is closely related to the tanning behavior of the solution.
SCOPE
1.1 This test method covers the determination of the titratable acidity of chromium tanning liquors. By titratable acidity  is meant not only free acidity, which is rarely present, but also anions combined with weakly basic cations such as Chromium (III), which can be titrated with base at the phenolphthalein end point.
1.2 This standard does not purport to address all of the safety problems, 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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Historical
Publication Date
09-May-2003
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Drafting Committee
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ASTM D3913-03 - Standard Test Method for Acidity in Basic Chromium Tanning Liquors
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NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.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:D3913–03
Standard Test Method for
1
Acidity in Basic Chromium Tanning Liquors
This standard is issued under the fixed designation D3913; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope hydroxyl in the solution being analyzed, is closely related to
the tanning behavior of the solution.
1.1 This test method covers the determination of the titrat-
able acidity of chromium tanning liquors. By titratable acidity
5. Interferences
is meant not only free acidity, which is rarely present, but also
5.1 Although for most purposes, the results of this analysis
anions combined with weakly basic cations such as Chromium
are intended to give a measure of the acid anions associated
(III),whichcanbetitratedwithbaseatthephenolphthaleinend
with chromium, it should be mentioned that any weak basic
point.
cation will behave similarly. Hence, aluminum, zirconium,
1.2 This standard does not purport to address all of the
ferric iron, and weak organic bases will all yield salts with
safety concerns, if any, associated with its use. It is the
acidity titratable by this test method.Adiscussion of the effect
responsibility of the user of this standard to establish appro-
4
of these interferences has been published.
priate safety and health practices and determine the applica-
5.2 If there are anions which form very stable complexes
bility of regulatory limitations prior to use.
with chromium present in the solution, the titration:
2. Referenced Documents
~x1y23!2 2
~CrOH X ~H O! ! 1 ~3 2 x!OH
x y 2 62x2y
→ 2
2.1 ASTM Standards:
Cr~OH! 1 yX 1 ~62x2y!H O (1)
← 3 2
D3898 Test Method for Chromic Oxide in Basic Chro-
2
where:
mium Tanning Liquors
X = stable complexes,
E180 Practice for Determining the Precision of ASTM
will not go to completion at the phenolphthalein endpoint and
Methods for theAnalysis and Testing of Industrial Chemi-
3
the acidity reported will be low. Large excess of oxalate or
cals
complexing anions of lesser affinity used for masking effect
5
3. Summary of Test Method
will introduce this error. To obviate this, an entirely different
method has been developed in which the hydroxyl groups are
3.1 A sample of suitable size is taken by diluting and
titratedandthechromiumiscompletelycomplexedbyoxalate.
aliquoting, if necessary. The sample is then heated to boiling
This is generally referred to as the Lehigh method and may be
and titrated hot to the first appearance of a pink color, stable to
,
67
used if complex ions are present in interfering amount.
boiling in the supernatant solution, as determined by viewing
the settled solution against the rim of a porcelain dish, or
6. Reagents and Materials
against the light in a tall beaker or Erlenmeyer flask.
6.1 Purity of Reagents—Reagent grade chemicals shall be
4. Significance and Use
used in all tests. Unless otherwise specified, it is intended that
all reagents shall conform to the specifications of the Commit-
4.1 Theacidityofachrometanningliquor,asdeterminedby
tee onAnalytical Reagents of theAmerican Chemical Society,
this test method, is rarely employed as such. This result is
8
where such specifications are available. Other grades may be
normally combined with the results of a chromium analysis
(seeTestMethodD3898)todetermineapropertyoftheliquor
calledbasicity.Thisproperty,equaltothepercentagebywhich
4
anions in a normal chromic salt have been replaced by
Hartford, W. H., JALCA, Vol 56, 1961, p. 568.
5
Thorstensen, T. C., and Theis, E. R., JALCA, Vol 47, 1952, p. 583.
6
Theis, E. R., and Thorstensen , T. C., Journal International Society Leather
Trade Chemists, Vol 31, 1947, p. 124.
1 7
ThistestmethodisunderthejurisdictionofASTMCommitteeD-31onLeather Serfass, E. J., Theis, E. R., and Clark, A., Jr., The Journal of the Leather
and is the direct responsibility of Subcommittee D31.06 on Chemical Analysis- Chemists Association, Vol 42, 1947, p. 360.
8
GeneralMethods.ThistestmethodwasdevelopedincooperationwiththeAmerican Reagent Chemicals, American Chemical Society Specifications, American
Leather Chemists Assoc. Chemical Society, Washington, DC. For suggestions on the testing of reagents not
Current edition approved May 10, 2003. Published July 2003. Originally listed by the American Chemical Society, see Analar Standards for Laboratory
approved in 1991. Last previous edition approved in 1993 as D3913–93 (1998). Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia
2
Annual Book of ASTM Standards, Vol 15.04. and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,
3
Annual Book of ASTM Standards, Vol 15.05. MD.
...

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