ASTM D5356-17a

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Designation: D5356 − 17 D5356 − 17a
Standard Test Method for
pH of Chrome Tanning Solutions
This standard is issued under the fixed designation D5356; 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.
1. Scope
1.1 This test method covers the determination of the pH of chrome tanning solutions.
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D3898 Test Method for Chromic Oxide in Basic Chromium Tanning Liquors
3. Terminology
3.1 Definitions of Terms Specific to This Standard:
3.1.1 pH, of a solution—the negative logarithm of the hydrogen ion activity.
This test method is under the jurisdiction of ASTM Committee D31 on Leather and is the direct responsibility of Subcommittee D31.06 on Chemical Analysis
Current edition approved May 15, 2017Sept. 1, 2017. Published May 2017October 2017. Originally approved in 1993. Last previous edition approved in 20152017 as
D5356 – 10D5356 – 17.(2015). DOI: 10.1520/D5356-17.10.1520/D5356-17A.
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 the ASTM website.
3.1.1.1 Discussion—
A solution of pH 7 is neutral at 24 °C. Lower numbers indicate increasing acidity, higher numbers indicate increasing alkalinity.
4. Summary of Test Method
4.1 The chrome tanning liquor is diluted to a concentration of 25.0 6 0.5 g chromic oxide equivalent per litre, allowed to come
to equilibrium and the pH is then measured with the appropriate meter.
5. Significance and Use
5.1 This test method is designed to measure the pH of a chrome tanning solution which has been diluted to a specific
concentration. This is considered to be a measure of the acidity or alkalinity of the solution.
5.2 This test method is suitable for quality control in the manufacture of leather.
6. Apparatus
6.1 Electronic pH Meter, either battery or line-operated equipped with appropriate electrodes. with a suitable electrode. The
meter shall have a maximum scale division ofan accuracy of at least 0.1 pH unit and reproducibility of 0.05 pH unit.
7. Reagents
7.1 Purity of Reagents—Reagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that all
reagents shall conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society, where
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D5356 − 17a
such specifications are available. Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high
purity to permit its use without lessening the accuracy of the determination.
7.2 Purity of Water—Unless otherwise indicated, references to water shall be understood to mean distilled water, deionized
water, or water of equal purity. Distilled water shall have a pH value of not less than 5.5 nor more than 7.0 and shall give a residue
of not more than 0.5 mg when 100 mL is evaporated and dried in a platinum dish.
7.3 Buffer Solutions—Commercially Standardized pH Solutions: Commerciallyavailable buffer solutions of 2.00 6 0.02 pH
and 4.00 6 0.02 pH shall be used for meter standardization, in accordance with the manufacturer’s recommendations.
7.3.1 Hydrochloric Acid (pH = 1.10 at 25 °C)—Add 2 g of concentrated hydrochloric acid (HCl, sp gr 1.10) to 450 g of water.
Standardize and dilute to 0.1 N.
7.3.2 Potassium Hydrogen Phthalate Buffer Solution (0.05 M, pH = 4.01 at 25 °C)—Dissolve 10.21 g of potassium hydrogen
phthalate (KHC H O ) in water and dilute to 1 L.
8 4 4
8. Standardization
8.1 Standardize the meter against the pH 4.00 standard, in accordance with the manufacturer’s recommendations. The buffer
standard shall be at room temperature and the temperature compensator shall be set at this temperature.
8.1 Read the Use manufacturer’s directions for establishing two point standardization with standard pH solut
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