BS 4427-6-1974 Methods of test for sodium tripolyphosphate (pentasodium triphosphate) and sodium pyrophosphate (tetrasodium pyrophosphate) for industrial use - Estimation of pyroph.pdf

1、BRITISH STANDARD BS 4427-6: 1974 Methods of test for Sodium tripolyphosphate (pentasodium triphosphate) and sodium pyrophosphate (tetrasodium pyrophosphate) for industrial use Part 6: Estimation of pyrophosphate content of sodium pyrophosphate UDC 661.833.456+661.833.458:546.33185:543.062:546.185324

2、BS4427-6:1974 This British Standard, having been approved by the ChemicalsIndustry Standards Committee, was published underthe authority of the Executive Board on 7June1974 BSI 11-1999 The following BSI references relate to the work on this standard: Committee reference CIC/25 Draft for comment 72/5

3、5290 ISBN 0 580 08021 8 Co-operating organizations The Chemicals Industry Standards Committee, under whose supervision this British Standard was prepared, consists of representatives of the following Government departments and scientific and industrial organizations: British Steel Industry Chemical

4、Industries Association* Department of Health and Social Security Department of Trade and Industry-Chemicals and Textiles Division Department of Trade and Industry-Laboratory of the Government Chemist* Fertiliser Manufacturers Association Limited* Ministry of Agriculture, Fisheries and Food National

5、Sulphuric Acid Association Royal Institute of Public Health and Hygiene Soap and Detergent Industry Association The Government department and industrial organizations marked with an asterisk in the above list, together with the following, were directly represented on the committee entrusted with the

6、 preparation of this BritishStandard: British Pharmacopoeia Commission Campden Food Preservation Research Association Flour Milling and Baking Research Association Institute of Metal Finishing National Association of Soft Drink Manufacturers Society for Water Treatment and Examination Textile Instit

7、ute Amendments issued since publication Amd. No. Date of issue CommentsBS4427-6:1974 BSI 11-1999 i Contents Page Co-operating organizations Inside front cover Foreword ii 1 Scope 1 2 Field of application 1 3 Principle 1 4 Reactions 1 5 Reagents 1 6 Apparatus 1 7 Procedure 1 8 Expression of results 2

8、 9 Test report 2 Publications referred to Inside back coverBS4427-6:1974 ii BSI 11-1999 Foreword This British Standard has been prepared under the authority of the Chemicals Industry Standards Committee in order to provide methods for the analysis of sodium tripolyphosphate and sodium pyrophosphate.

9、 For some years the UnitedKingdom has participated in the work of preparing methods of test applicable to sodium tripolyphosphate and sodium pyrophosphate for industrial use, organized by Subcommittee6 (formerly Working Group 7), “Phosphoric Acid and Condensed Phosphates” of Technical Committee47 “C

10、hemistry” of the International Organization for Standardization (ISO). As international agreement is reached on the methods, it is proposed to publish them as Parts of this British Standard. This Part is based on International Standard ISO2999 “Sodium pyrophosphate for industrial use Estimation of p

11、yrophosphate content Potentiometric method”, modified to take into account comments made by the UnitedKingdom during its development. This standard specifies methods of test only and should not be used or quoted as a specification defining limits of purity. Reference to the standard should be in a f

12、orm of words indicating that the methods of test used conform to the requirements of BS4427. 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 no

13、t of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages1 and 2, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This w

14、ill be indicated in the amendment table on the inside front cover.BS4427-6:1974 BSI 11-1999 1 1 Scope This Part of BS4427 specifies a potentiometric method for the estimation of the pyrophosphate content of tetrasodium pyrophosphate for industrial use. NOTEThe titles of the British Standards referre

15、d to in this Part are listed on the inside back cover. 2 Field of application The method is applicable to products containing at least90% of tetrasodium pyrophosphate and in the absence of more condensed forms of phosphates. 3 Principle The tetrasodium pyrophosphate decahydrate in a test portion is

16、converted to disodium dihydrogen pyrophosphate by addition of hydrochloric acid. Zinc sulphate solution is added to precipitate zinc pyrophosphate and form sulphuric acid. The sulphuric acid formed is potentiometrically titrated with standard volumetric sodium hydroxide solution. 4 Reactions Na 4 P

17、2 O 7+ 2HCl = Na 2 H 2 P 2 O 7+ 2NaCl Na 2 H 2 P 2 O 7 + 2ZnSO 4= Zn 2 P 2 O 7+ Na 2 SO 4+ H 2 SO 4 5 Reagents The reagents used shall be of a recognized analytical reagent quality. Water complying with the requirements of BS3978 shall be used in the test. 5.1 Sodium pyrophsophate, anhydrous. Heat a

18、bout20g of tetrasodium pyrophosphate decahydrate (Na 4 P 2 O 7 .10H 2 O) in a platinum crucible at about400 C until the mass is constant, after having checked its purity by, for example, paper chromatography. Grind the anhydrous salt obtained in a porcelain mortar and store in a clean and well-dried

19、 container. 5.2 Hydrochloric acid, approximately0.2N solution. 5.3 Zinc sulphate, approximately12.5% (m/m) solution, pH3.8. Dissolve125g of zinc sulphate heptahydrate (ZnSO 4 .7H 2 O) in875ml of water. Adjust to pH3.8, using the pH meter (6.1), with approximately0.1N sodium hydroxide solution or app

20、roximately0.1N sulphuric acid solution as appropriate. 5.4 Sodium hydroxide. 0.1N standard volumetric solution, calibrated against the anhydrous sodium pyrophosphate (5.1). 6 Apparatus Ordinary laboratory apparatus and the following are required. 6.1 pH meter, fitted with a glass electrode, sensitiv

21、ity0.05pH units. Essential performance requirements are given in BS2586, BS3145 and BS3422. 6.2 Magnetic stirrer, with PTFE coated rod. 7 Procedure 7.1 Test portion. Weigh, to the nearest0.0002g, 5g of the test portion. 7.2 Determination 7.2.1 Preparation of the test solution. Dissolve the test port

22、ion (7.1) in water, dilute to the mark in a500ml one-mark volumetric flask (see BS1792) and mix. Filter, if necessary, and take50.0ml of the solution. Introduce this aliquot portion into a250ml beaker and add40ml of water. Add slowly, with stirring, the hydrochloric acid solution (5.2) until the pH

23、reaches3.8, checking with the pH meter (6.1). Maintain the solution at25 1 C during the addition. Add 50ml of the zinc sulphate solution (5.3) at25 1 C and stir for about2min. 7.2.2 Titration. Titrate, restoring the pH to3.8 as follows. Very slowly add, drop by drop and using the magnetic stirrer (6

24、.2), the standard volumetric sodium hydroxide solution (5.4) until the pH reaches3.60. When the pH has reached3.60 stop the addition of the standard volumetric sodium hydroxide solution(5.4) and stir the solution for2min until equilibrium has been reached. Continue the titration until pH3.80, adding

25、 small quantities of the standard volumetric sodium hydroxide solution(5.4), allowing at least30s to elapse after each addition. 7.3 Calibration of the sodium hydroxide solution (5.4). Weigh, to the nearest0.0001g, 0.500g of the anhydrous sodiumpyrophosphate (5.1), place in a250ml beaker and add90ml

26、 of water. Slowly add, with stirring, the hydrochloric acid solution (5.2) until the pH reaches3.80, checking with the pH meter(6.1). Maintain the solution at25 2 C during the titration. Then follow the procedure described in7.2.1, starting “Add50ml of the zinc sulphate solution(5.3) .”, and7.2.2.BS

27、4427-6:1974 2 BSI 11-1999 The mass (m 2 ), in grams, of pyrophosphate corresponding to1ml of the sodium hydroxide solution (5.4) is given by the formula: Repeat this calibration three times and take the mean of the results. 8 Expression of results The pyrophosphate content, expressed as a percentage

28、 by mass of Na 4 P 2 O 7 , is given by the formula; 9 Test report The test report shall include the following particulars: a) the reference of the method used, i.e.BS4427-6; b) the results and the method of expression used; c) any unusual features noted during the determination; d) any operation not

29、 included in this British Standard or regarded as optional. where m 1 is the mass of anhydrous tetrasodium pyrophosphate (5.1) taken (g); V 1 is the volume of the sodium hydroxide solution (5.4) used for the titration (ml). m 2 m 1 V 1 - = V 2 m 2 D 100 m 0 - where V 2 is the volume of the standard

30、volumetric sodium hydroxide solution (5.4) used for the titration (ml); m 0 is the mass of the test portion (g); m 2 is the mass of anhydrous tetrasodium pyrophosphate corresponding to1ml of the standard volumetric sodium hydroxide solution (5.4) (g); D is the ratio between the volume of the test so

31、lution and the aliquot portion taken for the determination (see7.2).BS4427-6:1974 BSI 11-1999 Publications referred to This standard makes reference to the following British Standards: BS 1792, One-mark volumetric flasks. BS 2586, Glass electrodes for measurement of pH. BS 3145, Laboratory potentiom

32、etric pH meters. BS 3422, Laboratory deflection pH meters. BS 3978, Water for laboratory use. BS 4427-6: 1974 BSI 389 Chiswick High Road London W4 4AL BSIBritishStandardsInstitution BSI is the independent national body responsible for preparing BritishStandards. It presents the UK view on standards

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