1、BRITISHSTANDARD BS7319-10: 1990 Analysis of sodiumchloride forindustrial use Part 10: Method for determination of pH and total alkalinityBS7319-10:1990 This BritishStandard, having been prepared under the directionof the Chemicals Standards Policy Committee, waspublished under the authorityof the Bo
2、ard ofBSIandcomes into effect on 30September1990 BSI11-1999 The following BSI references relate to the work on this standard: Committee references CIC/22, FAC/23 Draft for comment88/55623DC ISBN 0 580 18543 5 Committees responsible for this BritishStandard The preparation of this BritishStandard was
3、 entrusted by the Chemicals Standards Policy Committee (CIC/-) to Technical Committee CIC/22, upon which the following bodies were represented: British Association for Chemical Specialities Chemical Industries Association Man-made Fibres Producers Committee Soap and Detergent Industry Association Te
4、xtile Research Council (FRCA) The following bodies were also represented in the drafting of the standard, through Technical Committee FAC/23: AFRC Institute of Food Research Creamery Proprietors Association Department of Trade and Industry (Laboratory of the Government Chemist) Food and Drink Federa
5、tion Milk Marketing Board for Northern Ireland Royal Association of British Dairy Farmers Salt Manufacturers Association Amendments issued since publication Amd. No. Date CommentsBS7319-10:1990 BSI 11-1999 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 Principle 1
6、3 Reagents 1 4 Apparatus 1 5 Procedure 1 6 Expression of results 2 7 Precision 2 Table 1 Results of pH analysis 2 Table 2 Results of alkalinity analysis 2 Publication(s) referred to Inside back coverBS7319-10:1990 ii BSI 11-1999 Foreword BS7319 has been prepared under the direction of the Chemicals
7、Standards Policy Committee, at the request of Technical Committee FAC/23, Salt, primarily to provide appropriate methods for determination of vacuum salt for food use as specified in BS998:1990. The methods for determination were previously published as appendices to BS998:1969. A list of the Parts
8、of BS7319 is given in Part1. This Part of BS7319 is based upon a method developed on behalf of the European Committee for the Study of Salt. It supersedes Appendix F of BS998:1969 which is withdrawn. A British Standard does not purport to include all the necessary provisions of a contract. Users of
9、British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, pages1 and 2, an inside back cover and a back co
10、ver. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.BS7319-10:1990 BSI 11-1999 1 1 Scope This Part of BS7319 specifies a potentiometric method for the measurement of the pH of a sod
11、ium chloride solution, of concentration100g/L, and for the determination of total alkalinity. The method is applicable to products of total alkalinity content, expressed as Na 2 CO 3 , of lower than1000mg/kg. NOTEThe titles of the publications referred to in this Part of this BritishStandard are lis
12、ted on the inside back cover. 2 Principle The principles of this Part of BS7319 are as follows: a) the measurement, at20 C, of the pH of a sodium chloride solution of concentration100g/L in water, using a pH meter fitted with a glass electrode and a calomel reference electrode; b) after the measurem
13、ent of pH, the addition of a known excess volume of standard hydrochloric acid; c) the removal of carbon dioxide by boiling; d) checking that the pH of the solution is less than3; e) titrating the excess acid with a standard sodium hydroxide solution to pH5, using a pH meter. 3 Reagents 3.1 General.
14、 Use only reagents of recognized analytical grade and water complying with grade3 of BS3978 freed from carbon dioxide by boiling and cooling to room temperature, or by bubbling through with nitrogen or with carbon dioxide-free air for10min. 3.2 Hydrochloric acid, standard volumetric solution c(HCl)=
15、0.1mol/L exactly. 3.3 Sodium hydroxide/barium chloride solution, standard volumetric solution, c(NaOH)=0.1mol/L exactly, free of carbonates. Add to each litre of a solution of sodium hydroxide, c(NaOH)=0.11mol/L approximately, contained in an aspirator fitted with a guard tube to absorb atmospheric
16、carbon dioxide,10mL of a solution containing100g/LBaCl 2 .2H 2 O. Mix the solution to react and leave it to stand until the precipitate of BaCO 3has settled at the bottom of the aspirator. Adjust the concentration to0.1moL/L NaOH exactly. 3.4 Sodium tetraborate buffer solution. Dissolve3.81 0.01g of
17、 sodium tetraborate decahydrate (Na 2 B 4 O 7 .10H 2 O) in water, transfer the solution quantitatively to a1000mL one-mark volumetric flask, dilute it to the mark with water and mix well. Protect this solution from carbon dioxide and prepare a fresh solution each month. The pH of this buffer solutio
18、n at20Cis9.22. 3.5 Potassium hydrogen phthalate buffer solution. Dissolve10.21 0.01g of potassium hydrogen phthalate (KHC 8 O 4 H 4 ) in water, transfer the solution quantitatively to a1000mL one-mark volumetric flask, dilute to the mark with water and mix well. Keep this solution in a well-sealed c
19、ontainer and protect it from carbon dioxide. The pH of this buffer solution at20 C is4.00. 3.6 Methyl red solution. Dissolve1g of methyl red in1L of95% (V/V) ethanol. 4 Apparatus 4.1 Ordinary laboratory apparatus 4.2 pH meter, fitted with a glass measuring electrode and a calomel reference electrode
20、, of sensitivity0.05pH units. 4.3 Mechanical or magnetic stirrer 4.4 Burette, capacity10mL, graduated in0.01mL. 5 Procedure 5.1 Test portion Weigh, to the nearest0.1g, a test portion of approximately25g. 5.2 Preparation of the test solution Introduce the test portion (see5.1) stirring slowly, with a
21、 mechanical or magnetic stirrer(4.3), into a400mL beaker containing250mL of water. Continue stirring until dissolution is complete. 5.3 Calibration of the pH meter Calibrate the pH meter(4.2) at20 1 C using the buffer solutions(3.4 and3.5). Rinse the electrodes well with water to remove all traces o
22、f the buffer solutions. 5.4 Measurement of pH Introduce into the beaker the two electrodes of the pH meter and carry out the measurement at a controlled temperature of20 1 C and with constant stirring, under the same conditions as the calibration (see5.3). 5.5 Determination of total alkalinity Remov
23、e the two electrodes and the stirrer(4.3) and add10.0mL of the standard hydrochloric acid(3.2). Boil for2min and cool to20 1 C.BS7319-10:1990 2 BSI 11-1999 Replace the two electrodes of the pH meter in the beaker. If the pH is not below3.00add a known further excess of the standard hydrochloric acid
24、(3.2) and boil again. Introduce the stirrer(4.3) and titrate the excess acid with the standard sodium hydroxide/barium chloride solution(3.3) to pH5. Keep this solution for the blank test (see5.6). NOTEIf the determination of the pH is not to be carried out, replace the pH meter with five drops of m
25、ethyl red solution(3.6) and titrate with a colour change from red to orange at the end point. It is important to check that initially the pH was lower than3, using indicator paper. 5.6 Blank test Remove the two electrodes and the stirrer(4.3) from the solution obtained after the titration(see5.5), a
26、nd add the same volume of standard hydrochloric acid used in the determination(see5.5). Boil for2min, cool to20 1 C and back-titrate under the same conditions as5.5. 6 Expression of results 6.1 pH Express the results of this measurement in pH units, to the nearest0.1pH unit. 6.2 Total alkalinity, ex
27、pressed as Na 2 CO 3 Calculate the total alkalinity, expressed as milligrams of Na 2 CO 3per kilogram of sodium chloride on a moisture free basis, using the following expression: Express the results to the nearest milligram per kilogram. 7 Precision Analyses carried out on two samples gave the stati
28、stical results shown in Table 1and Table 2, each laboratory having given two results obtained by the same operator on two test samples. Table 1 Results of pH analysis Table 2 Results of alkalinity analysis where V 0 is the volume of the standard sodium hydroxide/barium chloride solution(3.3) used fo
29、r the blank test (see5.6) (inmL); V 1 is the volume of the standard sodium hydroxide/barium chloride solution(3.3) used for the determination (see5.5) (inmL); m is the mass of the test portion (see5.1) (ing); H is the moisture content determined in accordance with BS7319-2 in%(m/m). Sample Number of
30、 laboratories Mean Repeatability r Reproducibility R Vacuum salt 16 8.90 0.04 0.33 Sea salt 16 8.85 0.05 0.32 Sample Number of laboratories Mean Repeatability r Reproducibility R Vacuum salt 13 100 8 11 Sea salt 13 210 7 15BS7319-10:1990 BSI 11-1999 Publication(s) referred to BS998, Specification fo
31、r vacuum salt for food use 1) . BS3978, Specification for water for laboratory use. BS7319, Analysis of sodium chloride for industrial use. BS7319-1, Method for determination of sodium chloride content. 1) Referred to in the foreword only.BS7319-10: 1990 BSI 389 Chiswick High Road London W4 4AL BSIB
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