1、BRITISH STANDARD BS4258-13: 1990 Methods of test for Phosphoric acid (orthophosphoric acid) for industrial use Part 13: Determination of soluble sulphate content (potentiometric method) UDC 661.634:543.4.062:546.226:543.257.3:620.1BS4258-13:1990 This British Standard, having been prepared under the
2、directionof the Chemicals Standards Policy Committee, waspublished under the authorityof the Board of BSI andcomes into effect on 31July1990 BSI 11-1999 The following BSI references relate to the work on this standard: Committee reference CIC/37 Draft for comment 87/50973 DC ISBN 0 580 18605 9 Commi
3、ttees responsible for this British Standard The preparation of this British Standard was entrusted by the Chemicals Standards Policy Committee (CIC/-) to Technical Committee CIC/37 upon which the following bodies were represented: Association of Public Analysts British Coal Corporation Chemical Indu
4、stries Association Department of Trade and Industry (Laboratory of the Government Chemist) Fertiliser Manufacturers Association Limited Institute of Trading Standards Administration Ministry of Agriculture, Fisheries and Food Ministry of Defence Amendments issued since publication Amd. No. Date Comm
5、entsBS4258-13:1990 BSI 11-1999 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 Principle 1 3 Reagents 1 4 Apparatus 1 5 Procedure 1 6 Expression of results 3 7 Test report 3 Table 1 Example of table used for determination of end-point and titre 2 Publications referr
6、ed to Inside back coverBS4258-13:1990 ii BSI 11-1999 Foreword This Part of BS4258 has been prepared under the direction of the Chemicals Standards Policy Committee. It describes a method of test for phosphoric acid (orthophosphoric acid) derived by the “wet process”, in which sulphate contents are g
7、enerally higher than in phosphoric acid (orthophosphoric acid) derived by the “thermal process”. For products having sulphate contents below0.4% (m/m), the method described in BS4258-3, by which the total sulphate content is determined, is applicable. A British Standard does not purport to include a
8、ll the necessary provisions of a contract. Users of 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, pages i an
9、d ii, pages1 to 4, aninside back cover and a back cover. 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.BS4258-13:1990 BSI 11-1999 1 1 Scope This Part of BS4258describes a potentiom
10、etric method for the determination of the soluble sulphate content of phosphoric acid (orthophosphoric acid) for industrial use. The method is applicable to products having sulphate contents, expressed as SO 4 , not lower than0.4% (m/m). NOTEThe titles of the publications referred to in this Part of
11、 this standard are listed on the inside back cover. 2 Principle Removal of phosphate from the sample by a controlled precipitation titration with lithium hydroxide solution, followed by filtration to remove the precipitate. Titration of the sulphate remaining in the filtrate with a solution of bariu
12、m perchlorate, the end point being determined by potentiometry. 3 Reagents Use reagents of recognized analytical grade and water complying with grade3of BS3978. 3.1 Orthophosphoric acid solution, 1.75g/mL, approximately about88% (m/m). 3.2 Lithium hydroxide solution, c(Li(OH) 2 ) = 100g/L. 3.3 Hydro
13、chloric acid solution, c(HCl) = 20g/L, approximately. 3.4 Sodium hydroxide solution, c(NaOH) = 20g/L, approximately. 3.5 Propan-2-ol 3.6 Sodium sulphate solution, corresponding to1.0g of sulphate per litre. Dry sodium sulphate for2h at105 2 C. Weigh1.4786g into a1000mL one-mark volumetric flask, dis
14、solve in water and dilute to the mark. Mix thoroughly. NOTE1mL of this solution contains1mg of sulphate. 3.7 Barium perchlorate solution, c(Ba(ClO) 4 ) 2 )=0.02mol/L, approximately. Weigh7.0g of Ba(ClO 4 ) 2 .3H 2O into a1000mL one-mark volumetric flask. Add50mL of water and mix. Once dissolved, dil
15、ute to the mark with water. Standardize this solution by following the procedure described in 5.3, using10.0mL of the sodium sulphate solution (3.6) in place of the test solution and determine the titrant volume, V (see clause 6). 3.8 Phenolphthalein indicator, 10g/L solution in ethanol. NOTEFor the
16、 purposes of 3.8, the ethanol may be replaced by industrial methylated spirits95% (V/V) complying with BS3591. It should be noted that the use of industrial methylated spirits is governed by the Methylated Spirits Regulations, 1983 (S.I. 1983No. 252). It is not permissible to use duty-free ethanol,
17、received under the provisions of the Alcoholic Liquors Duties Act1972, Section10, for purposes for which industrial methylated spirits is an acceptable alternative. 4 Apparatus 4.1 Ordinary laboratory apparatus 4.2 Magnetic stirrer, fitted with a hot plate and a PTFE-coated stirrer bar40mm long. 4.3
18、 Ion activity/pH meter, with glass and reference electrodes. 4.4 Two platinum electrodes NOTETo avoid any electrode drift, the electrodes should have been lightly polished using a proprietary abrasive strip. 4.5 Bchner funnel, 60mm in diameter. 4.6 Glass microfibre filter pads, 60mm in diameter. 4.7
19、 Two one-mark volumetric flasks, 250mL, complying with BS1792, class B. 5 Procedure 5.1 Test portion Weigh, to the nearest0.001g, a test portion containing between100mg and200mg of sulphate and not more than15g of diphosphorus pentaoxide. 5.2 Preparation of the test solution Place the test portion (
20、5.1) into a250mL beaker and dilute to approximately50mL with water. Add several drops of the phenolphthalein indicator solution (3.8). Place the beaker on the magnetic stirrer (4.2), insert the stirrer bar and commence stirring. Add, from a burette, the lithium hydroxide solution(3.2) at a rate of10
21、mL to15mL/min untilthe solution is just pink. Place the pH electrodes(4.3) into the solution and continue to addthe lithium hydroxide solution until the pH reaches11.6 0.1. Note the volume, V 1 , in millilitres, of lithium hydroxide solution added. Remove the pH electrodes and rinse them into the be
22、aker with a little water. Continue the stirring and warm the solution to80 5 C on a hotplate. Cool the beaker and solution to room temperature in a stream of water. Filter the solution under suction through three of the filter pads (4.6) contained in the Bchner funnel (4.5). Wash the beaker and the
23、filter with water without exceeding a total volume of200mL.BS4258-13:1990 2 BSI 11-1999 Transfer the filtrate quantitatively to the250mL one-mark volumetric flask (4.7), dilute to the mark with water and mix thoroughly. 5.3 Preparation of the blank solution Follow the procedure described in 5.2, rep
24、lacing the test portion with between2.5g and3.0g of the orthophosphoric acid (3.1) and recording the volume, V 2in millilitres, of lithium hydroxide solution (3.2) added. 5.4 Determination of the test solution 5.4.1 Measurement solution Take an aliquot portion of the test solution (5.2) containing a
25、pproximately10mg of sulphate and place this in a100mL beaker. Dilute to25mL if necessary and add50mL of the propan-2-ol (3.5). Place the beaker on the magnetic stirrer, insert the magnetic stirrer bar, commence stirring and introduce the pH electrodes. Adjust the pH of the solution to3.5 0.1using th
26、e hydrochloric acid solution (3.3) or the sodium hydroxide solution (3.4). Remove the pH electrodes and rinse them into the beaker with about5mL of water. 5.4.2 Titration Introduce the platinum electrodes (4.4) into the measurement solution (see 5.4.1). Set the meter (4.3) for potentiometric titrati
27、on, referring to the operating manual as necessary. While continuing the stirring, add the barium perchlorate solution (3.7), in1mL portions, from the burette, noting the meter reading after each addition. Towards the expected end-point reduce the portions added to0.1mL, continuing to note the meter
28、 readings. Continue this procedure until the differences, % 1 E, in millivolts, between successive readings remain essentially constant. Record the volume of barium perchlorate solution added and the corresponding millivolt readings and construct a table as shown in Table 1. Calculate the successive
29、 differences, % 1 E, and record these. The end-point of the titration is given by the largest increase, % 2 E, between the values of % 1 E. Table 1 Example of table used for determination of end-point and titre From the table prepared, determine the volume, V 3 , in millilitres, of titrant added, at
30、 the exact end-point of the titration, from the following expression: NOTEThe titration procedure may be simplified by the use of an automatic titration apparatus fitted with a recorder, to give adirect indication of the end-point. Titrant volume Meter reading % 1 E % 2 E mL mV mV mV 0 620 9 1.0 629
31、 6 3 2.0 635 5 1 3.0 640 8 3 4.0 648 7 1 5.0 655 8 1 5.1 663 7 1 5.2 670 15 8 5.3 685 9 6 5.4 694 6 3 5.5 700 5 1 5.6 705 In this example V 3is evaluated as follows. where a is the largest positive value of % 2 E (in mV); b is the first value of % 2 E following a (in mV); C is the increment of bariu
32、m perchlorate solution (3.7) added which gave rise to the largest value of % 1 E (in mL); D is the volume of barium perchlorate solution (3.7) which had been added prior to addition of the increment C (in mL).BS4258-13:1990 BSI 11-1999 3 5.5 Determination of the blank solution 5.5.1 Blank measuremen
33、t solution Follow the procedure described in 5.4.1 taking10.0mL of the standard sodium sulphate solution (3.6), and adding a15.0mL aliquot portion of the blank solution (5.3) in place of the test solution (5.2). 5.5.2 Titration Follow the procedure described in 5.4.2, using the blank solution (see 5
34、.5.1). Determine the titre, V 4in millilitres, at the exact end-point of the titration. Calculate the blank value, V O , (in mL) as the volume of barium perchlorate solution (3.7) corresponding to1mL of lithium hydroxide solution(3.2) from the following expression: 6 Expression of results The sulpha
35、te content of the orthophosphoric acid, expressed as a percentage by mass of SO 4 , is given by the following expression: Inserting the values for m sand V 6 , this simplifies to 7 Test report The test report shall include the following information: a) a complete identification of the test sample; b
36、) a reference to this Part of this BritishStandard, i.e. BS4258-13:1990; c) the results expressed in accordance with clause 6; d) any unusual features noted during the determination; e) any operation not included in this Part of this British Standard or regarded as optional. where V is the volume of
37、 barium perchlorate solution corresponding to10.0mL of sodium sulphate solution (see 3.7) (in mL); V 2 is the volume of lithium hydroxide solution(3.3) used in the preparation of the blank solution (5.3) (in mL); V 4 is the volume of barium perchlorate solution(3.7) used in the blank determination (
38、in mL); V a is the volume of the blank solution (in mL), i.e. 250mL; V b is the volume of the aliquot portion taken from the blank solution (in mL), i.e. 15mL where m is the mass of the test portion (in g) (see5.1); m s is the mass of the SO 4in10.0mL of sodium sulphate solution (3.6) (in mg), i.e.1
39、0mg; V is the volume of the barium perchlorate solution corresponding to10.0mL of the sodium sulphate solution (in mL) (see 3.7); V O is the blank value corresponding to1mL of lithium hydroxide solution (in mL) (see5.5.2); V 4 V V 2 - V a V b - V 1 is the volume of lithium hydroxide solution used in
40、 the preparation of the test solution (in mL) (see 5.2); V 3 is the volume of the barium perchlorate solution used in the actual determination (inmL) (see 5.4.2); V 5 is the volume of the aliquot of the test solution taken for the actual determination (in mL) (see 5.4.2); V 6 is the volume of the te
41、st solution (in mL) (see 5.2), i.e.250mL.4 blankBS4258-13:1990 BSI 11-1999 Publications referred to BS 1792, Specification for one-mark volumetric flasks. BS 3591, Specification for industrial methylated spirits. BS 3978, Specification for water for laboratory use. BS 4258, Methods of test for phosp
42、horic acid (orthophosphoric acid) for industrial use. BS 4258-3, Determination of sulphate content. BS 4258-13: 1990 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 sta
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