1、Designation: D3913 03 (Reapproved 2015)Standard Test Method forAcidity in Basic Chromium Tanning Liquors1This standard is issued under the fixed designation D3913; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last re
2、vision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers the determination of the titrat-able acidity of chromium tanning liquors. By titratable acidityis mea
3、nt not only free acidity, which is rarely present, but alsoanions combined with weakly basic cations such as Chromium(III), which can be titrated with base at the phenolphthalein endpoint.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in t
4、hisstandard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2.
5、Referenced Documents2.1 ASTM Standards:2D3898 Test Method for Chromic Oxide in Basic ChromiumTanning Liquors3. Summary of Test Method3.1 A sample of suitable size is taken by diluting andaliquoting, if necessary. The sample is then heated to boilingand titrated hot to the first appearance of a pink
6、color, stable toboiling in the supernatant solution, as determined by viewingthe settled solution against the rim of a porcelain dish, oragainst the light in a tall beaker or Erlenmeyer flask.4. Significance and Use4.1 The acidity of a chrome tanning liquor, as determined bythis test method, is rare
7、ly employed as such. This result isnormally combined with the results of a chromium analysis(see Test Method D3898) to determine a property of the liquorcalled basicity. This property, equal to the percentage by whichanions in a normal chromic salt have been replaced byhydroxyl in the solution being
8、 analyzed, is closely related tothe tanning behavior of the solution.5. Interferences5.1 Although for most purposes, the results of this analysisare intended to give a measure of the acid anions associatedwith chromium, it should be mentioned that any weak basiccation will behave similarly. Hence, a
9、luminum, zirconium,ferric iron, and weak organic bases will all yield salts withacidity titratable by this test method. A discussion of the effectof these interferences has been published.35.2 If there are anions which form very stable complexeswith chromium present in the solution, the titration:Cr
10、OHxXyH2O!62x2y!x1y23!213 2 x!OH2(1)CrOH!31yX216 2 x 2 y!H2Owhere:X = stable complexes,will not go to completion at the phenolphthalein endpointand the acidity reported will be low. Large excess of oxalate orcomplexing anions of lesser affinity used for masking effectwill introduce this error.4To obv
11、iate this, an entirely differentmethod has been developed in which the hydroxyl groups aretitrated and the chromium is completely complexed by oxalate.This is generally referred to as the Lehigh method and may beused if complex ions are present in interfering amount.5,66. Reagents and Materials6.1 P
12、urity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise specified, it is intended thatall reagents shall conform to the specifications of the Commit-tee on Analytical Reagents of the American Chemical Society,1This test method is under the jurisdiction ofASTM Committee D
13、31 on Leatherand is the direct responsibility of Subcommittee D31.06 on Chemical Analysis Thistest method was developed in cooperation with the American Leather ChemistsAssoc.Current edition approved Sept. 1, 2015. Published October 2015. Originallyapproved in 1991. Last previous edition approved in
14、 2009 as D3913 03 (2009).DOI: 10.1520/D3913-03R15.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Hartford,
15、W. H., JALCA, Vol 56, 1961, p. 568.4Thorstensen, T. C., and Theis, E. R., JALCA, Vol 47, 1952, p. 583.5Theis, E. R., and Thorstensen , T. C., Journal International Society LeatherTrade Chemists, Vol 31, 1947, p. 124.6Serfass, E. J., Theis, E. R., and Clark, A., Jr., The Journal of the LeatherChemist
16、s Association, Vol 42, 1947, p. 360.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1where such specifications are available.7Other grades may beused, provided it is first ascertained that the reagent is ofsufficient high purity to per
17、mit its use without lessening theaccuracy of the determination.6.2 Purity of WaterUnless otherwise specified, referenceto water shall be understood to mean distilled water or water ofequal purity.6.3 Sodium Hydroxide, 0.1 NDissolve 42 g NaOH inabout 60 mL water. Cool and transfer to a 100-mL volumet
18、ricflask; dilute to the mark, stopper, mix, and allow any turbidityto settle. Pipet 10 mL of the clear solution to a 1-L volumetricflask; dilute to mark and mix well. Keep stoppered andprotected from atmospheric carbon dioxide.6.3.1 StandardizationDry potassium hydrogen phthalate,KHC8H4O4, in an ove
19、n for2hat120C and cool in desiccator.Weigh about 0.8 g to an accuracy of 0.1 mg into a 400-mL tallbeaker or Erlenmeyer flask. Dissolve in 200 to 250-mL waterand titrate with the sodium hydroxide to be standardized, usingphenolphthalein indicator.normality of sodium hydroxide 5weight K phthalate0.204
20、23 3mL titration(2)6.4 Phenolphthalein Indicator, 5 %Dissolve 5 g phenol-phthalein in 100 mL 95 % ethanol.7. Procedure7.1 The results are more meaningful if the same sampleused for the chromium determination is used for the aciditydetermination; for example, a specimen that consists of aweighed quan
21、tity of the liquor diluted to a definite volumecontaining from 0.003 to 0.004 g of chromic oxide permillilitre. Transfer 25-mL aliquots for testing.7.2 Two procedures have been found about equally effectivefor determining the endpoint. The results differ slightly, asshown in the section on precision
22、 and bias. Hence, the resultsby the two procedures cannot be compared exactly.7.3 Procedure 1Transfer the 25-mL aliquot to a 7-in.porcelain casserole. Add 400 mL water and 1 mL 5 %phenolphthalein. Boil and titrate while boiling with standard-ized 0.1 N sodium hydroxide until a faint pink color, as s
23、een atthe side of the casserole after settling, persists for one minute.7.4 Procedure 2Transfer the 25-mLaliquot into a 400-mLtall beaker. Dilute to 250 mL. Heat to boiling, remove from theheat, add 10 drops 5 % phenolphthalein and titrate until a pinkcolor is barely noted. Boil again for ten minute
24、s and retitrateuntil a faint pink color is barely noted on settling. Boil a thirdtime and complete the titration. (The process may be expeditedby using two, preferably three, aliquots of the sample, in whichone is titrated according to the above procedure, and the othershave 0.5 mL increments of add
25、itional 0.1 N NaOH added.Interpolate the end point after the second boiling.8. Calculation8.1 Calculate acidity in milliequivalents per millilitre oforiginal sample as follows:Acidity, me/mL 5A 3 NW3V25(3)where:A = the number of mL of standard sodium hydroxiderequired to titrate the 25 mL aliquot of
26、 the specimen,N = the normality of the sodium hydroxide solution,W = the weight of the specimen before dilution, g, andV = the volume to which W was diluted, mL.NOTE 1The acidity in me/mL is numerically equal to equivalents/litreor normality.8.2 Unless otherwise specified, test two 25 mL aliquotsfro
27、m the diluted specimen.8.3 The acidity in the sample for the test shall be the averageof the test results obtained from the two aliquots tested.8.4 Record the acidity to the nearest 0.1 %.9. Precision and Bias9.1 The precision of this test method, as determined byanalysis of variance on a round robi
28、n test using triplicatedeterminations on four samples in three laboratories gave thefollowing deviations, expressed as a percentage of the aciditypresent:Procedure I Procedure IIRepeatability (within laboratories) 0.48 0.72Reproducibility (between laboratories) 1.84 2.789.2 Although an attempt was m
29、ade to refer the results of thistest to knowns and so determine accuracy, the analysis ofvariance shows a significant variability attributable to samplemakeup (variations in acidity, formate, and sugar content). Thisamounts to an estimated standard deviation, 2.6 and 2.86 % byProcedure I and Procedu
30、re II, respectively. The overall averagebias for all samples is 0.46 % for Procedure I and 0.94 % forProcedure II.10. Keywords10.1 acidity; basic chromium tanning liquor; basicity7Reagent Chemicals, American Chemical Society Specifications , AmericanChemical Society, Washington, DC. For suggestions
31、on the testing of reagents notlisted by the American Chemical Society, see Analar Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.D3913 03 (2015)2ASTM International ta
32、kes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own r
33、esponsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addre
34、ssed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at t
35、he address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org). Permission rights to photocopy the standard may also be secured from the Copyright Clearance Center, 222Rosewood Drive, Danvers, MA 01923, Tel: (978) 646-2600; http:/ 03 (2015)3
