BS 1647-1-1984 pH measurement - Specification for pH scale《pH值测量 第1部分 pH值标度规范》.pdf

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1、BRITISH STANDARD BS 1647-1: 1984 Incorporating Amendment No. 1 pH measurement Part 1: Specification for pH scale Confirmed February 2012BS1647-1:1984 This British Standard, having been prepared under the directionof the Laboratory Apparatus Standards Committee,was published underthe authority of the

2、 Board ofBSI and comes into effect on 31December 1984 BSI 08-1999 First published as BS 1647 May1950 First revision August 1961 Second Part revision Part 1 December 1984 The following BSI references relate to the work on this standard: Committee reference LBC/16 Draft for comment 79/55106 ISBN 0 580

3、 14099 7 Committees responsible for this British Standard The preparation of this British Standard was entrusted by the Laboratory Apparatus Standards Committee (LBC/-) to Technical Committee LBC/16 upon which the following bodies were represented: British Kinematograph, Sound and Television Society

4、 British Pharmacopoeia Commission Chemical Industries Association Department of Trade and Industry (National Physical Laboratory) Electricity Supply Industry in England and Wales GAMBICA (BEAMA Ltd.) Institute of Medical Laboratory Sciences Royal Society of Chemistry Sira Ltd. Society for Applied Ba

5、cteriology Society of Chemical Industry Society of Dairy Technology Society of Glass Technology University of Newcastle-upon-Tyne Amendments issued since publication Amd. No. Date of issue Comments 5567 May 1987 Indicated by a sideline in the marginBS1647-1:1984 BSI 08-1999 i Contents Page Committee

6、s responsible Inside front cover Foreword ii 1 Scope 1 2 Definitions 1 3 pH scale 2 4 Reference value standard solution 2 5 Slope factor 3 Appendix A Interpretation of pH measurements 4 Appendix B Outline procedures for measurement of pH values 6 Appendix C Bibliography 7 Table 1 Accuracy classes fo

7、r pH measurements 2 Table 2 pH values of the reference value standard solution at various temperatures 3 Table 3 Values of the slope factor 3 Publications referred to Inside back coverBS1647-1:1984 ii BSI 08-1999 Foreword This British Standard was first published in1950 and was prepared by a technic

8、al committee directly under the aegis of the Chemical Divisional Council following recommendations made at a conference, held in 1948 at the request of the Royal Society, to discuss the need for a standard pH scale. It was revised in1961 to extend the temperature range covered in the definition of p

9、H from between0 C and60 C to between0 C and95 C. This revision, in two Parts, of BS1647 has been prepared under the direction of the Laboratory Apparatus Standards Committee by the technical committee responsible for BS2586 and BS3145. This Part, together with Part 2, supersedes BS1647:1961 which is

10、 withdrawn. At the time of preparation of this revision of this British Standard, discussions were under way with a view to harmonizing the standards and recommendations were being prepared by four international organizations. These were: Subcommittee 1 (General methods) of TC 47 (Chemistry) of the

11、International Organization for Standardization (ISO), Subcommittee D (Analysing equipment) of TC 66 (Electronic measuring equipment) of the International Electrotechnical Commission (IEC), the International Organization for Legal Metrology (OIML) and the International Union for Pure and Applied Chem

12、istry (IUPAC). The technical committee responsible for this Part of this standard played a leading role in this work and, as a safe-guard against the possibility of agreement not being reached in the short term, recommended the publication of this revision. It is based on a critical re-examination o

13、f some of the earlier experimental work and on new work carried out at the University of Newcastle-upon-Tyne. The object of this Part of this standard is to ensure that, when different workers refer to a stated value of pH to two or more decimal places, they mean the same thing to within0.01 in the

14、temperature range0 C to60 C and approaching0.01 at higher temperatures. It is occasionally desirable to measure and to quote pH values to more than two decimal places, but the significance of such additional figures may sometimes be uncertain. The principal change in this revision is to include more

15、 details of the procedures for making pH measurements in order that they may have the greatest possible reproducibility and repeatability. The definition adopted for pH is an operational one,i.e. it is based on the operation used to determine it using an electrochemical cell, referred to as the “ope

16、rational cell” in this Part of this standard. No simple physical interpretation of pH values can be made in terms of either hydrogen ion concentration or hydrogen ion activity except when the test solution is a dilute aqueous electrolyte solution of simple composition. For this reason, pH should be

17、regarded as simply a reproducible scale related to “acidity”, and this is all that is required for most technological purposes. For the interpretation of pH values, see Appendix A. When the test solution contains organic matter, suspended or dissolved, reproducibility may not be high but is usually

18、adequate for the purposes for which the pH measurement is required. The definition of the pH scale in terms of a single reference value standard solution has been reaffirmed. This definition differs from most other definitions of pH scales given in national standards (seereview 1) which, in common w

19、ith the scale adopted by the National Bureau of Standards (NBS), USA 2 are multi-standard scales. Nevertheless, within0.02, and possibly less, in the pH range3 to9 and the temperature range0 C to60 C, there is no practical difference between the pH scale defined in this Part of this standard and the

20、 NBS recommendations. A general account of the problems of pH standardization and measurement can be found elsewhere (see3 and 4). The pH value of an unknown solution is measured with a pH meter against the pH scale specified in this standard using the operational standard solutions specified in Par

21、t 2 of this standard for calibration of the pH meter.BS1647-1:1984 BSI 08-1999 iii A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itsel

22、f confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i to iv, pages 1 to 8, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indi

23、cated in the amendment table on the inside front cover.iv blankBS1647-1:1984 BSI 08-1999 1 1 Scope This Part of BS1647 specifies requirements for a pH scale in terms of a single reference value standard aqueous solution of potassium hydrogen phthalate with a molality of0.05mol/kg, and the (theoretic

24、al) slope factor. This pH scale is appropriate for pH measurements of aqueous solutions at temperatures in the range0 C to95 C using, for calibration, the operational standard solutions specified in Part 2 of this standard. NOTE 1Practical pH measurements are based on one or more of the operational

25、reference standard solutions according to circumstances and the reference value standard solution is included in the list of operational standard reference solutions from which the choice is to be made. NOTE 2The procedures described in Appendix B are suitable for all pH measurements, including thos

26、e where other solvents and suspended matter are present, but where the electrode system is calibrated against reference materials in aqueous solution. A.4 gives information about scales for non-aqueous and mixed aqueous solvents. The best repeatability generally obtainable is 0.003 but may be consid

27、erably worse than this in solutions containing reactive materials and suspended matter, especially at the extremes of the pH range0 to14 and at temperatures above60 C. Guidance on interpretation of pH measurements is given in Appendix A and guidance on accuracy of pH measurements is given in Appendi

28、x B. NOTE 3The titles of the publications referred to in this Part of this standard are listed on the inside back cover. 2 Definitions For the purposes of this Part of BS1647 the following definitions apply. 2.1 operational pH cell an electrochemical cell that is the basis of practical pH measuremen

29、ts, consisting of an electrode responsive to hydrogen ions (hydrogen gas electrode, or glass electrode) and a reference electrode dipping into the test solution 2.2 reference electrode an external electrode system that incorporates a filling solution and a means, such as a ceramic plug or frit, of f

30、orming the liquid junction NOTEUsually this reference system has either a mercury/calomel (dimercury dichloride) or a silver/silver chloride inner element in contact with a concentrated solution of potassium chloride as filling solution. 2.3 liquid junction any junction between two electrolyte solut

31、ions of different composition NOTEAcross such a junction there arises a potential difference called the liquid junction potential. In the operational cell (2.1) the junction is between the test solution or the pH standard reference solution and the filling solution or the bridge solution(2.5) of the

32、 reference electrode. 2.4 filling solution (of a reference electrode) a solution containing the anion to which the reference electrode of the operational pH cell is reversible,e.g. chloride for the silver/silver chloride electrode NOTEIn the absence of a bridge solution (2.5), a high concentration o

33、f filling solution, comprising cations and anions of almost equal mobility, is employed as a means of maintaining a small and approximately constant liquid junction potential on substitution of the test solution for the standard reference solution(s). 2.5 bridge solution (of a double junction refere

34、nce electrode) a solution of high concentration of an inert salt, preferably comprising cations and anions of almost equal mobility, optionally interposed between the reference electrode filling solution (2.4) and both the test solution and the standard reference solution, when the test solution and

35、 the filling solution are chemically incompatible NOTEThis procedure introduces a second liquid junction into the operational cell and is usually formed in a similar way to the first. 2.6 residual liquid junction (potential) error an error arising from the assumption that the liquid junction potenti

36、al does not vary with the composition and concentration of the test and standard solutions 2.7 pH glass electrode an electrode responsive to hydrogen ions, usually consisting of a bulb, or other suitable form, of special glass attached to a stem of high resistance material with internal reference el

37、ectrode and internal filling solution system (seeBS2586) NOTEOther geometrical forms may be appropriate for special applications, e.g. a capillary electrode for measuring the pH of blood. 2.8 pH meter a high impedance instrument by means of which either the pH of a solution or the potential differen

38、ce between a pair of electrodes immersed in a solution is indicated (seeBS3145).BS1647-1:1984 2 BSI 08-1999 2.9 slope factor, k the temperature-dependent proportionality factor between potential and pH, calculated from the expression (In 10) RT/F where NOTEThe slope factor is tabulated in Table 3. 2

39、.10 pH reference value standard solution a solution that is the basis for the definition of a pH scale in the temperature range0 C to95 C 2.11 pH operational reference standard solutions solutions with pH values assigned by the operational cell method (see Part 2 of this standard) with reference to

40、values of the reference value pH standard at each temperature 2.12 internal reference electrode (of a pH glass electrode) an electrode,e.g. silver/silver chloride, terminating the screened input cable of the pH meter, and in contact with the internal filling solution 2.13 test solution the solution

41、of which the pH value is required 2.14 accuracy class a classification of pH measurements, the accuracy of which is designated by a number representing the limit of error expressed as a percentage of the upper limit of the normal range of pH (0to14) as given in Table 1 Table 1 Accuracy classes for p

42、H measurements 3 pH scale The pH scale shall be a straight line drawn through a single pH value at a particular temperature specified for the reference value standard solution as specified in clause 4 and having a slope factor as specified in clause 5. NOTEThe procedure by which pH values have been

43、assigned to this reference value standard solution is that specified in Part 2 of this standard. The convention of Bates and Guggenheim 5 has been adopted for the single ion activity coefficient of the chloride ion using equation (1). where 4 Reference value standard solution The reference value sta

44、ndard solution shall consist of0.05mol of potassium hydrogen phthalate in1kg of pure water, prepared as specified in Part 2 of this standard. The pH value of the reference value standard solution at any temperature in the range0Cto95 C shall be in accordance with the following equation: where NOTE 1

45、Values of the pH of the reference value standard solution at various temperatures are given in Table 2. NOTE 2Values of the pH reference value standard solution for the temperature range100 C to 200 C, not covered by this standard, have been reported 6. NOTE 3Equation (2) is based on recent work 7 t

46、aking note of earlier work 8, 9, 10. pH values shall not differ from the values given in Table 1 by more than 0.003 at 25 C, by more than 0.005 between 5 C and20 C, by more than 0.01 between30 C and 65 C and by more than 0.02 above65 C. R is the universal gas constant; T is the absolute temperature;

47、 F is the Faraday constant. Accuracy class Tolerance of pH value, 0.02 0.1 0.3 1.5 0.003 0.014 0.042 0.20 lg* cl = AI 1/2 /1 + 1.5I 1/2 (1) I is the ionic strength (not greater than 0.1 molkg 1 ); A is the temperature dependent parameter of the Debye Huckel Theory (A = 0.5108 mol 1/2 kg 1/2at 25 C).

48、 pH(S) = A + B (T 298.15) + C (T 298.15) 2 (2) T = temperature (in K); A = 4.00480; B = 0.0010007; C = 0.000032745.BS1647-1:1984 BSI 08-1999 3 Table 2 pH values of the reference value standard solution at various temperatures 5 Slope factor The slope factor, k, shall be in accordance with the follow

49、ing equation: where NOTEValues of k at various temperatures are given in Table 3. Table 3 Values of the slope factor Temperature, t pH Temperature, t pH C C 0 5 10 15 20 25 30 35 37 40 45 4.000 3.998 3.997 3.998 4.001 4.005 4.011 4.018 4.022 4.027 4.038 50 55 60 65 70 75 80 85 90 95 4.050 4.064 4.080 4.097 4.116 4.137 4.159 4.183 4.21 4.24 (3) R is the universal gas constant = 8.31441 JK 1mol 1 ; T is the temperature (in K); F is the Faraday constant = 9.648456 10 4Cmol 1 ; In 10 = 2.302585