BS-5688-14-1979 ISO-3119-1976.pdf
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1、BRITISH STANDARD BS 5688-14: 1979 ISO 3119:1976 Methods of test for Boric acid, boric oxide, disodium tetraborates, sodium perborates and crude sodium borates for industrial use Part 14: Determination of chromium content of boric acid, boric oxide and disodium tetraborates ISO title: Boric acid, bor
2、ic oxide and disodium tetraborates for industrial use Determination of chromium content Diphenylcarbazide photometric method NOTEIt is recommended that this Part be read in conjunction with the information in the “General introduction”, published separately as BS 5688-0. UDC 661.65:546.273:543.062:5
3、46.76 Licensed Copy: sheffieldun sheffieldun, na, Mon Dec 04 15:49:21 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 5688-14:1979 This British Standard, having been prepared under the direction of the Chemicals Standards Committee, was published under the authority of the Executive Board on 28 Februa
4、ry 1979 BSI 12-1999 The following BSI references relate to the work on this standard: Committee reference CIC/16 Draft for comment 74/53496 DC ISBN 0 580 10547 4 National foreword This Part of BS 5688 is identical with ISO 3119 “Boric acid, boric oxide and disodium tetraborate for industrial use Det
5、ermination of chromium content Diphenylcarbazide photometric method” published by the International Organization for Standardization (ISO). Terminology and conventions. The text of the International Standard has been approved as suitable for publication, without deviation, as a British Standard. Som
6、e terminology and certain conventions are not identical with those used in British Standards; attention is drawn to the following. The comma has been used throughout as a decimal marker. In British Standards it is current practice to use a full point on the baseline as the decimal marker. Where the
7、words “International Standard” appear, referring to this standard, they should be interpreted as “British Standard”. Additional information Water. Water complying with the requirements of clause 3 is specified in BS 3978 “Water for laboratory use”. Reagents. Sulphuric acid, approximately 1.84 g/ml,
8、about 98 % (m/m) solution, which is the corresponding reagent normally obtainable in the United Kingdom, is suitable for use in place of the solution specified in 3.3. Similarly, phosphoric acid, approximately 1.75 g/ml, about 90 % (m/m) solution, is suitable for use in place of the solution specifi
9、ed in 3.4. Principle. In addition to the reactions described in clause 2, it should be noted that the chromium present in the test solution is oxidized to the hexavalent state with ammonium persulphate prior to reaction with diphenylcarbazide. A British Standard does not purport to include all the n
10、ecessary 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 and ii, pa
11、ges 1 and 2 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. Amendments issued since publication Amd. No.Date of issueComments Licensed Copy: sheffieldun sheffieldu
12、n, na, Mon Dec 04 15:49:21 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 5688-14:1979 BSI 12-1999i Contents Page National forewordInside front cover 1Scope and field of application1 2Principle1 3Reagents1 4Apparatus1 5Procedure1 6Expression of results2 7Test report2 Licensed Copy: sheffieldun sheffi
13、eldun, na, Mon Dec 04 15:49:21 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ii blank Licensed Copy: sheffieldun sheffieldun, na, Mon Dec 04 15:49:21 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 5688-14:1979 BSI 12-19991 1 Scope and field of application This International Standard specifies a diphenyl
14、carbazide photometric method for the determination of the chromium content of boric acid, boric oxide and disodium tetraborates for industrial use. 2 Principle Fusion of a test portion with sodium carbonate followed by neutralization with sulphuric acid. Measurement of the absorbance, at a wavelengt
15、h of about 540 nm, of the complex formed by chromium with diphenylcarbazide, sodium azide being added to destroy any colour due to manganese present in the sample. 3 Reagents During the analysis use only reagents of recognized analytical reagent grade and only distilled water, or water of equivalent
16、 purity. 3.1 Ammonium persulphate 3.2 Sodium carbonate, anhydrous. 3.3 Sulphuric acid, approximately 1,84 g/ml, about 96 % (m/m) solution, diluted 1 + 1 by volume. 3.4 Phosphoric acid, approximately 1,70 g/ml, about 85 % (m/m) solution, diluted 1 + 1 by volume. 3.5 Diphenylcarbazide, 2 g/l solution.
17、 Dissolve 0,2 g of diphenylcarbazide melting point in the range 175 3 C and molar absorptivity for the chromium complex (CrO4) of about 42 000 in 10 ml of glacial acetic acid ( 1,05 g/ml), approximately 17,4 N solution, and dilute with water to 100 ml. Prepare this solution immediately before use. 3
18、.6 Silver nitrate, 25 g/l solution. 3.7 Sodium azide, 50 g/l solution. 3.8 Chromium, standard solution, corresponding to 0,10 g of Cr per litre. Dissolve 0,282 9 g of potassium dichromate, previously dried at 105 C and cooled in a desiccator, in water, add 0,2 g of the sodium carbonate (3.2) and dil
19、ute to the mark in a 1 000 ml one-mark volumetric flask. 1 ml of this standard solution contains 100 4g of Cr. 3.9 Chromium, standard solution, corresponding to 0,001 0 g of Cr per litre. Dilute 10,0 ml of the standard chromium solution (3.8) to the mark in a 1 000 ml one-mark volumetric flask. 1 ml
20、 of this standard solution contains 1 4g of Cr. 4 Apparatus Ordinary laboratory apparatus and 4.1 Platinum dish, about 100 ml capacity, with platinum lid. 4.2 Spectrophotometer, fitted with cells of 4 cm optical path length, or 4.3 Photoelectric absorptiometer, fitted with the same cells and with fi
21、lters allowing a maximum transmission at about 540 nm. 4.4 pH meter 5 Procedure 5.1 Test portion Weigh, to the nearest 0,01 g, approximately 2 g of the test sample into the platinum dish (4.1). 5.2 Blank test Carry out a blank test at the same time as the determination, following the same procedure
22、and using the same quantities of all the reagents as used for the determination. 5.3 Preparation of calibration graph 5.3.1 Preparation of standard colorimetric solutions, for photometric measurements with cells of 4 cm optical path length. Into a series of six 100 ml one-mark volumetric flasks, tra
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