1、BRITISH STANDARD BS 6075-4: 1981 ISO 984:1974 Methods of Sampling and test for sodium hydroxide for industrial use Part 4: Determination of silica content ISO title: Sodium hydroxide for industrial use Determination of silica content Reduced silico-molybdic complex photometric method NOTEIt is recom
2、mended that this Part be read in conjunction with the information in the “Generalintroduction” published separately as BS6075-0. UDC 661.322.1:546.33 36:543.42.062:546.284 31BS6075-4:1981 This British Standard, having been prepared under the directionof the Chemicals Standards Committee, was publish
3、ed under the authority ofthe Executive Board and comesinto effect on 27February1981 BSI 11-1999 The following BSI references relate to the work on this standard: Committee reference CIC/22 Draft for comment 73/54863 DC ISBN 0 580 12054 6 Amendments issued since publication Amd. No. Date of issue Com
4、mentsBS6075-4:1981 BSI 11-1999 i Contents Page National foreword ii 1 Scope and field of application 1 2 Reference 1 3 Principle 1 4 Reagents 1 5 Apparatus 1 6 Procedure 2 7 Expression of results 3 8 Test report 3 Publications referred to Inside back coverBS6075-4:1981 ii BSI 11-1999 National forewo
5、rd This Part of BS6075 is identical with ISO984 “Sodium hydroxide for industrial use Determination of silica content Reduced silico-molybdic complex photometric method”, published in1974 by the International Organization for Standardization (ISO). Terminology and conventions. The text of the Interna
6、tional Standard has been approved as suitable for publication as a British Standard without deviation. Some terminology and certain conventions are not identical with those used in British Standards; attention is especially drawn to the following. The comma has been used throughout as a decimal mark
7、er. In British Standards it is current practice to use a full point on the baseline as the decimal marker. Wherever the words “International Standard” appear, referring to this standard, they should be read as “British Standard”. Additional information Water. Water complying with the requirements of
8、 clause4 is specified in BS3978“Water for laboratory use”. Calibration graph. For some grades of sodium hydroxide it may be necessary to adjust the range of the calibration graph (see6.3) to cover the expected silica content. In BS4130 “Sodium hydroxide (technical grades)” details of a suitable rang
9、e for the grades specified are given. 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 itself confer immunity from legal obligations. Cro
10、ss-reference International Standard Corresponding British Standard BS 6075 Methods of sampling and test for sodium hydroxide for industrial use ISO 3195:1975 Part 5:1981 Sampling and preparation of main test solution (Identical) Summary of pages This document comprises a front cover, an inside front
11、 cover, pages i and ii, pages1 to 4, 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 indicated in the amendment table on the inside front cover.BS6075-4:1981 BSI 11-1999 1 1 Scope and field of applicati
12、on This International Standard specifies a reduced silico-molybdic complex photometric method for the determination of the silica content of sodium hydroxide for industrial use. The method is applicable to products having silica (SiO 2 ) contents exceeding10mg/kg. 2 Reference ISO 3195, Sodium hydrox
13、ide for industrial use Sampling Test sample Preparation of the main solution for carrying out certain determinations 1) . 3 Principle Formation of the yellow oxidized silico-molybdic complex at pH1,1 0,2, in the presence of boric acid to suppress interference by fluorides. Selective reduction of thi
14、s complex with a mixtureofamino-naphthol sulphonic acid (4-amino-3-hydroxynaph-thalene-1-sulphonic acid), sodium metabisulphite and sodium sulphite, in the presence of oxalic acid and in a strongly acid medium so as to suppress interference by phosphates. Photometric measurement of the blue-coloured
15、 complex at a wavelength of about795nm. 4 Reagents During the analysis use only reagents of recognized analytical reagent grade and only demineralized water. Store all the reagents in polyethylene bottles. 4.1 Sulphuric acid, approximately9N solution. 4.2 Hydrochloric acid, approximately2N solution.
16、 4.3 Boric acid, saturated solution (about48g/l). 4.4 Oxalic acid, 100g/l solution. 4.5 Sodium molybdate dihydrate Na 2 MoO 4 .2H 2 O,140g/l solution. Dissolve35g of this reagent in200ml of water at about50 C in a polyethylene beaker. Cool to room temperature, transfer to a250ml one-mark volumetric
17、flask, dilute to the mark and mix. Transfer to a polyethylene bottle. If necessary, filter the solution before use. 4.6 Reducing solution 4.6.1 Dissolve7g of anhydrous sodium sulphitein50ml of water. Then add1,5g of4-amino-3-hydroxynaphthalene-1-sulphonic acidand dissolve by trituration. 4.6.2 Disso
18、lve 90 g of anhydrous sodium metabisulphite in 900 ml of water. Mix the two solutions (4.6.1) and (4.6.2) and dilute to1000ml. Filter, if necessary, store the solution in a cool place away from direct sunlight and renew it every15 to20days. 4.7 Sodium chloride, 70 g/l solution. 4.8 Silica, standard
19、solution corresponding to0,500g of SiO 2per litre. In a platinum crucible, weigh, to the nearest0,001g: either0,500g of silica (SiO 2 ) produced from silicic acid (H 2 SiO 3 ) calcined at1000 C to constant mass and cooled in a desiccator; or0,500g of pure quartz, finely ground and previously calcine
20、d for1h at1000 C and cooled in a desiccator. Add 5 g of anhydrous sodium carbonate to the crucible. Mix well, preferably with a platinum spatula, and fuse carefully. Allow to cool, add warm water, heat moderately until completely dissolved, cool, transfer quantitatively to a1000ml one-mark volumetri
21、c flask, dilute to the mark and mix. Transfer immediately to a polyethylene bottle. 1 ml of this standard solution contains0,500mg ofSiO 2 . 4.9 Silica, standard solution corresponding to10mg of SiO 2per litre. Take 20,0 ml of the standard silica solution (4.8), transfer into a1000ml one-mark volume
22、tric flask, dilute to the mark and mix. 1 ml of this standard solution contains0,010mg ofSiO 2 . Prepare this standard solution at the time of use. 4.10 Phenolphthalein, 10g/l solution in95% (V/V) ethanol. 5 Apparatus Ordinary laboratory apparatus and 5.1 Spectrophotometer or 5.2 Photoelectric absor
23、ptiometer with2cm cells and fitted with suitable filters ensuring a maximum transmission at about795nm. NOTEIf such filters are not available, operate at about680nm, with4cm cells. 1) At present at the stage of draft.BS6075-4:1981 2 BSI 11-1999 6 Procedure 6.1 Test portion 6.1.1 Weigh, to the neares
24、t0,01g, in a100ml polyethylene beaker,13 0,1g of the solution A (see4.3 of ISO3195) stored in a silica-free vessel and containing40g of the test sample in1000ml. During this operation, prevent the solution from coming into contact with glass. 6.1.2 In addition, determine the mass, to the nearest0,01
25、g, of10,0ml of the solution A, taken with the aid of a pipette or a burette, to enable the mass of the test portion (6.1.1) to be converted to a volume when the results are calculated. 6.2 Blank test Carry out a blank test at the same time as the determination, following the same procedure and using
26、 the same quantities of all the reagents used for the determination (6.4) but replacing the10,0ml of the solution A by10,0ml of the sodium chloride solution (4.7). 6.3 Preparation of calibration curve 6.3.1 Preparation of the standard colorimetric solution, for photometric measurements with2cm cells
27、 at a wavelength of about795nm or with4cm cells for photometric measurements at about680nm. Into a series of four100ml polyethylene beakers, introduce the volumes of the standard silica solution(4.9) shown in the following table: Treat the contents of each beaker as follows. Add 10,0 ml of the sodiu
28、m chloride solution (4.7), dilute to25ml and add, swirling after each addition,7,5ml of the hydrochloric acid solution(4.2),20ml of the boric acid solution (4.3) and10ml of the sodium molybdate solution (4.5). The pH of the solution should now be about1,1. Wait10min and then add, swirling after each
29、 addition,5ml of the oxalic acid solution (4.4) and20ml of the sulphuric acid solution (4.1). Allow to stand for2min, then add2ml of the reducing solution (4.6), transfer quantitatively to a100ml one-mark volumetric flask, dilute to the mark and mix. 6.3.2 Photometric measurements After at least10mi
30、n, but not more than40min, carry out the photometric measurements using thespectrophotometer (5.1), at a wavelength ofabout795nm, or the photoelectric absorptiometer (5.2), fitted with suitable filters, after having adjusted the instrument to zero absorbance against the compensation solution. 6.3.3
31、Preparation of the calibration chart Plot a graph having, for example, the numbers of milligrams of silica (SiO 2 ) contained in100ml of standard colorimetric solutions on the abscissa and the corresponding values of absorbance on the ordinate. 6.4 Determination 6.4.1 Colour development Add 1 drop o
32、f the phenolphthalein solution (4.10) to the test portion (6.1), already contained in a100ml polyethylene beaker, and neutralize with the hydrochloric acid solution (4.2). Add10ml of water and, swirling after each addition,7,5ml of the hydrochloric acid solution (4.2),20ml of the boric acid solution
33、 (4.3) and10ml of the sodium molybdate solution (4.5). Wait for10min then add, swirling after each addition,5ml of the oxalic acid solution (4.4) and20ml of the sulphuric acid solution (4.1). Allow to stand for2min, then add2ml of the reducing solution (4.6), transfer quantitatively to a100ml one-ma
34、rk volumetric flask, dilute to the mark and mix. 6.4.2 Photometric measurement After at least 10 min, but not more than40min, carry out the photometric measurement according to the procedure specified in6.3.2, after having adjusted the instrument to zero absorbance against the blank test solution (6
35、.2). Standard silica solution(4.9) Corresponding mass of SiO 2 ml mg 0 a 2,0 5,0 10,0 0 0,02 0,05 0,10 a Compensation solutionBS6075-4:1981 BSI 11-1999 3 7 Expression of results By means of the calibration curve (6.3.3), determine the quantity of SiO 2corresponding to the value of the photometric me
36、asurement. The silica content, expressed as milligrams of silica (SiO 2 ) per kilogram, is given by the formula where m 0 is the mass, in grams, of the test sample used to prepare solution A; m 1 is the mass, in milligrams, of SiO 2found by the determination; m 2 is the mass, in grams, of the test p
37、ortion(6.1.1); m 3 is the mass, in grams, of10,0ml of solution A (see4.3 of ISO3195), determined by the procedure specified in6.1.2. 8 Test report The test report shall include the following particulars: a) the reference of the method used; b) the results and the method of expression used; c) any un
38、usual features noted during the determination; d) any operation not included in this International Standard or the International Standard to which reference is made, or regarded as optional.4 blankBS6075-4:1981 BSI 11-1999 Publications referred to See national foreword.BS 6075-4: 1981 ISO984:1974 BS
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