ASTM D8032-20

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it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D8032 − 16 D8032 − 20
Standard Test Method for
Acid Number of Terephthalic Acid by Color-Indicator
Titration
This standard is issued under the fixed designation D8032; 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 Scope*
1.1 This test method covers the determination of acid number of terephthalic acid (TA) by color-indicator titration. Acid number
of TA product is usually within 674 to 676 mg KOH/g.
1.2 In determining the conformance of the test results using this method, results shall be rounded off in accordance with the
rounding-off method of Practice E29.
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.4 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.
1.5 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:
D974 Test Method for Acid and Base Number by Color-Indicator Titration
D1193 Specification for Reagent Water
D4790 Terminology of Aromatic Hydrocarbons and Related Chemicals
D6809 Guide for Quality Control and Quality Assurance Procedures for Aromatic Hydrocarbons and Related Materials
E29 Practice for Using Significant Digits in Test Data to Determine Conformance with Specifications
E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods
E300 Practice for Sampling Industrial Chemicals
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
2.2 Other Document:
OSHA Regulations, 29 CFR paragraphs 1910.1000 and 1910.1200
This test method is under the jurisdiction of ASTM Committee D16 on Aromatic Hydrocarbons Aromatic, Industrial, Specialty and Related Chemicals and is the direct
responsibility of Subcommittee D16.02 on Oxygenated Aromatics.
Current edition approved March 1, 2016Aug. 1, 2020. Published June 2016September 2020. Originally approved in 2016. Last previous edition approved in 2016 as
D8032 – 16. DOI: 10.1520/D8032-16.10.1520/D8032-20.
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.
Available from U.S. Government Printing Office, Superintendent of Documents, 732 N. Capitol St., NW, Washington, DC 20401-0001, http://www.access.gpo.gov.
*A Summary of Changes section appears at the end of this standard
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D8032 − 20
3. Terminology
3.1 Definitions:
3.1.1 acid number, n—the quantity of base, expressed in milligrams of potassium hydroxide per gram of sample that is required
to titrate a sample in a specified solvent to a specified end point.
4. Summary of Test Method
4.1 A TA sample is dissolved in dimethyl sulfoxide and titrated with standard sodium hydroxide solution to the end point indicated
by the color change of the added phenolphtalein solution (colorless in acid and pink in base). The acid number is calculated as
milligrams of KOH per gram of TA sample. Its theoretical value of TA sample is 675.5 mg KOH/g.
5. Significance and Use
5.1 An estimate of TA purity can be determined by titrating with KOH. As an index of TA purity, the acid number can be used
as a guide in the quality control of TA production.
6. Apparatus
6.1 Analytical Balance, capable of weighing 60.0001 g.
6.2 Burets, 50-mL with 0.1-mL graduations.
7. Reagents
7.1 Purity of Reagents—Unless otherwise indicated, it is intended that all reagents shall conform to the reagent grade specification
of the Analytical Reagents of the American Chemical Society, where such specifications are available. Other grades may be used,
provided it is first ascertained that the reagent is of sufficient high purity to permit its use without lessening the performance or
accuracy of the determination. Reagent chemicals shall be used for all tests.
7.2 Purity of Water—Unless otherwise indicated, references to water shall be understood to mean Type III of Specification D1193.
Boil the water gently for 5 to 10 min to remove any CO and cool the water to room temperature.
7.3 Dimethyl Sulfoxide—(Warning—WarningFlammable—Flammable and harmful if inhaled, swallowed or absorbed through
the skin.).
7.4 Sodium Hydroxide Solution (0.5 M)—Weigh 20 g of sodium hydroxide (NaOH) (Warning—WarningHighly—Highly
corrosive to all body tissue.) in a beaker. Add 100 mL water (boiling gently for 5 to 10 min and cooling to room temperature, free
of CO ) to dissolve and cool the solution. Then quantitatively transfer the solution into a 1000 mL volumetric flask and dilute to
volume with the above water. The NaOH solution should be stored in a plastic bottle and stopper must be stressed.
NOTE 1—After standardization, the NaOH solution should not be stored in a glass container because it will be slowly neutralized from exposure to a glass
container. It will also “cement” a glass stopper into a glass container.
7.5 Ethanol.
7.6 Phenolphthalein Indicator Solution (1 g/L)—Dissolve 0.1 g solid phenolphthalein in 100 mL ethanol.
7.7 Potassium Hydrogen Phthalate.
Reagent Chemicals, American Chemical Society Specifications,ACS Reagent Chemicals, Specifications and Procedures for Reagents and Standard-Grade Reference
Materials, American Chemical Society, Washington, DC. For suggestions on the testing of reagents not listed by the American Chemical Society, see Analar Standards for
Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC),
Rockville, MD.
D8032 − 20
8. Hazards
8.1 Consult current federal regulations, supplier’s Safety Data Sheets, and local regulations for all materials used in this test
method.
9. Sampling, Test Specimens, and Test Units
9.1 Use only representative samples obtained as described in Practice E300, unless otherwise specified.
10. Standardization of Titrant
10.1 Place 10 to 20 g of primary standard potassium hydrogen phthalate in a weighing bottle and dry at 120°
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