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2、n American National StandardStandard Test Methods forAcidity or Alkalinity of Water1This standard is issued under the fixed designation D 1067; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in
3、parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.1. Scope*1.1 These test methods2 cover the determination of acidity or alka
4、linity of all types of water. Three test methods are given as follows:SectionsTest Method A (Electrometric Titration)7 to 15Test Method B (Electrometric or Color-Change Titration)16 to 24applications. When titrating to a selected end point dictated bypractical considerations, (1) only a part of the
5、actual neutral- izing capacity of the water may be measured, or (2) this capacity may actually be exceeded in arriving at optimum acidity or alkalinity conditions.1.4 A scope section is provided in each test method as a guide. It is the responsibility of the analyst to determine theTest Method C (Co
6、lor-Change Titration After HydrogenPeroxide Oxidation and Boiling)25 to 33acceptability of these test methods for each matrix.1.5 Former Test Methods C (Color-Comparison Titration)1.2 In all of these test methods the hydrogen or hydroxylions present in water by virtue of the dissociation or hydrolys
7、is of its solutes, or both, are neutralized by titration with standard alkali (acidity) or acid (alkalinity). Of the three procedures, Test Method A is the most precise and accurate. It is used to develop an electrometric titration curve (sometimes referred to as a pH curve), which defines the acidi
8、ty or alkalinity of the sample and indicates inflection points and buffering capacity, if any. In addition, the acidity or alkalinity can be determined with respect to any pH of particular interest. The other two methods are used to determine acidity or alkalinity relative toa predesignated end poin
9、t based on the change in color of an internal indicator or the equivalent end point measured by a pH meter. They are suitable for routine control purposes.1.3 When titrating to a specific end point, the choice of end point will require a careful analysis of the titration curve, the effects of any an
10、ticipated changes in composition on the titration curve, knowledge of the intended uses or disposition of the water, and a knowledge of the characteristics of the process controls involved. While inflection points (rapid changes in pH) are usually preferred for accurate analysis of sample compositio
11、n and obtaining the best precision, the use of an inflection point for process control may result in significant errors in chemical treatment or process control in some1 These test methods are under the jurisdiction of ASTM Committee D19 on Water and are the responsibility of Subcommittee D19.05 on
12、Inorganic Constituents in Water.Current edition approved Jan. 10, 2002. Published April 2002. Originally published as D 1067 49. Last previous edition D 1067 92(96).and D (Color-Change Titration After Boiling) were discontin-ued. Refer to Appendix X4 for historical information.1.6 This standard does
13、 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 appro- priate safety and health practices and determine the applica- bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM S
14、tandards:D 596 Practice for Reporting Results of Analysis of Water3D 1129 Terminology Relating to Water3D 1192 Specification for Equipment for Sampling Water and Steam in Closed Conduits3D 1193 Specification for Reagent Water3D 1293 Test Methods for pH of Water3D 2777 Practice for Determination of P
15、recision and Bias ofApplicable Methods of Committee D-19 on Water3D 3370 Practices for Sampling Water from Closed Con- duits3D 5847 Practice for Writing Quality Control Specifications for Standard Test Methods for Water Analysis4E 200 Practice for Preparation, Standardization, and Stor- age of Stand
16、ard and Reagent Solutions for Chemical Analysis53. Terminology3.1 DefinitionsThe terms in these test methods are defined in accordance with Terminology D 1129.2 The basic procedures used in these test methods have appeared widespread in the technical literature for many years. Only the particular ad
17、aptation of theelectrometric titration appearing as the Referee Method is believed to be largely the work of Committee D-19.3 Annual Book of ASTM Standards, Vol 11.01.4 Annual Book of ASTM Standards , Vol 11.02.5 Annual Book of ASTM Standards, Vol 15.05.*A Summary of Changes section appears at the e
18、nd of this standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.1D 1067 023.1.1 Certain uses of terminology exist in the water treat-ment industry which may differ from these definitions. Adiscussion of terms is presented in Appen
19、dix X1.4. Significance and Use4.1 Acidity and alkalinity measurements are used to assist in establishing levels of chemical treatment to control scale, corrosion, and other adverse chemical equilibria.4.2 Levels of acidity or alkalinity are critical in establishing solubilities of some metals, toxic
20、ity of some metals, and the buffering capacity of some waters.5. Purity of Reagents5.1 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
21、 Society, where such specifications are available.6 Other grades may be used, pro- vided it is first ascertained that the reagent is of sufficiently high purity to permit its use without lessening the accuracy of the determination.5.2 Unless otherwise indicated, references to water shall be understo
22、od to mean reagent water conforming to Specification D 1193, Type I. In addition, reagent water for this test shall be free of carbon dioxide (CO2) and shall have a pH between 6.2 and 7.2 at 25C. Other reagent water types may be used provided it is first ascertained that the water is of sufficiently
23、 high purity to permit its use without adversely affecting the precision and bias of the test method. Type III water was specified at the time of round robin testing of this test method.A procedure for the preparation of carbon dioxide-free water is given in Practice E 200.6. Sampling6.1 Collect the
24、 sample in accordance with SpecificationD 1192 and Practices D 3370 as applicable.6.2 The time interval between sampling and analysis shall be as short as practically possible in all cases. It is mandatory that analyses by Test Method A be carried out the same day the samples are taken; essentially
25、immediate analysis is desirable for those waste waters containing hydrolyzable salts that contain cations in several oxidation states.TEST METHOD AELECTROMETRIC TITRATION7. Scope7.1 This test method is applicable to the determination of acidity or alkalinity of all waters that are free of constituen
26、ts that interfere with electrometric pH measurements. It is used for the development of a titration curve that will define inflection points and indicate buffering capacity, if any. The6 Reagent Chemicals, American Chemical Society Specifications, American Chemical Society, Washington, DC. For sugge
27、stions 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 Pharmacopoeia and National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville, MD.acidity or alkalinity of
28、the water or that relative to a particularpH is determined from the curve.8. Summary of Test Method8.1 To develop a titration curve that will properly identify the inflection points, standard acid or alkali is added to the sample in small increments and a pH reading is taken after each addition. The
29、 cumulative volume of solution added is plotted against the observed pH values. All pH measurements are made electrometrically.9. Interferences9.1 Although oily matter, soaps, suspended solids, and other waste materials may interfere with the pH measurement, these materials may not be removed to inc
30、rease precision, because some are an important component of the acid- or alkali- consuming property of the sample. Similarly, the development of a precipitate during titration may make the glass electrode sluggish and cause high results.10. Apparatus10.1 Electrometric pH Measurement Apparatus, confo
31、rm- ing to the requirements given in Test Methods D 1293.11. Reagents 611.1 Hydrochloric Acid, Standard (0.02 N) (see Note 1) Prepare and standardize as directed in Practice E 200, except that the titration shall be made electrometrically. The inflection point corresponding to the complete titration
32、 of carbonic acid salts will be very close to pH 3.9.NOTE 1Sulfuric acid of similar normality may be used instead of hydrochloric acid. Prepare and standardize in like manner.11.2 Sodium Hydroxide, Standard (0.02 N)Prepare and standardize as directed in Practice E 200, except that the titration shal
33、l be made electrometrically. The inflection point corresponding to the complete titration of the phthalic acid salt will be very close to pH 8.6.12. Procedure12.1 Mount the glass and reference electrodes in two of the holes of a clean, threehole rubber stopper chosen to fit a300-mL, tall-form Berzel
34、ius beaker without spout, or equiva- lent apparatus. Place the electrodes in the beaker and standard- ize the pH meter, using a reference buffer having a pH approximating that expected for the sample (see Test Methods D 1293). Rinse the electrodes, first with reagent water, then with a portion of th
35、e sample. Following the final rinse, drain the beaker and electrodes completely.12.2 Pipette 100 mL of the sample, adjusted, if necessary, to room temperature, into the beaker through the third hole in the stopper. Hold the tip of the pipette near the bottom of the beaker while discharging the sampl
36、e.12.3 Measure the pH of the sample in accordance with TestMethods D 1293.12.4 Add either 0.02 N acid or alkali solution, as indicated, in increments of 0.5 mL or less (see Note 2). After each addition, mix the solution thoroughly. Determine the pH when the mixture has reached equilibrium as indicat
37、ed by a constant2D 1067 02TABLE 1 Determination of Precision and Bias for Acidity and15.2 The collaborative test of this test method was per- Alkalinity by Electrometric Titration (Test Method A)formed in reagent waters by six laboratories using one operatorAmountAdded, meq/LAmountFound, meq/LStSoAc
38、idityBias,%each, using three levels of concentration for both the acidityand alkalinity.15.3 Precision and bias for this test method conforms to48.3048.761.250.44+0.9423.0022.610.680.271.6717.1016.510.710.263.47Alkalinity4.905.000.390.12+2.122.462.450.140.060.000.510.560.150.05+10.59Practice D 27777
39、7, which was in place at the time ofcollaborative testing. Under the allowances made in 1.4 of D277798, these precision and bias data do meet existing requirements for interlaboratory studies of Committee D19 test methods.reading (see Note 3). Mechanical stirring, preferably of themagnetic type, is
40、required for this operation; mixing by means of a gas stream is not permitted. Continue the titration until the necessary data for the titration curve have been obtained.NOTE 2If the sample requires appreciably more than 25 mL of standard solution for its titration, use a 0.1 N solution, prepared an
41、d standardized in the same manner (see Practice E 200).NOTE 3An electrometric titration curve is smooth, with the pH changing progressively in a single direction, if equilibrium is achieved after each incremental addition of titrant, and may contain one or more inflection points. Ragged or irregular
42、 curves may indicate that equilibrium was not attained before adding succeeding increments. The time required will vary with different waters as the reaction rate constants of different chemical equilibria vary. In some instances the reaction time may be an interval of a few seconds while other slow
43、er, more complex reactions may require much longer intervals. It is important, therefore, that the period be sufficient to allow for any significant pH changes, yet consistent with good laboratory practices.12.5 To develop a titration curve, plot the cumulative milliliters of standard solution added
44、 to the sample aliquot against the observed pH values. The acidity or alkalinity relative to a particular pH may be determined from the curve.13. Calculation13.1 Calculate the acidity or alkalinity, in milliequivalents per liter, using Eq 1:Acidity or alkalinity!, meq/L epm!5 AN 3 10(1)where:A = sta
45、ndard acid or alkali required for the titration, mL,andN = normality of the standard solution.14. Report14.1 Report the results of titrations to specific end points as follows: “The acidity (or alkalinity) to pH at C = meq/L(epm).”14.2 Appropriate factors for converting milliequivalents per liter (e
46、pm) to other units are given in Practice D 596.15. Precision and Bias 715.1 The precision and bias data presented in Table 1 for this test method meet the requirements of Practice D 2777.7 Supporting data are available from ASTM Headquarters. Request RR:D19-1149.TEST METHOD BELECTROMETRIC ORCOLOR-CHANGE TITRATION16. Scope16.1 This test method covers the rapid, routine control me
