BS 4341-1968 Methods of test for formic acid《甲酸的试验方法》.pdf
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1、BRITISH STANDARD BS4341:1968 Methods of test for Formic acidBS4341:1968 This BritishStandard, having been circulated to the ChemicalsIndustry StandardsCommittee and endorsed by the Chairman oftheChemical Divisional Council, was published undertheauthority of the GeneralCouncil on 19 September1968 BS
2、I 12-1999 The following BSI reference relates to the work on this standard: Committee reference CIC/4/2 ISBN 0 580 00278 0 Co-operating organizations The Chemicals Industry Standards Committee, under whose supervision the formulation of the United Kingdom point of view in the international work lead
3、ing to the publication of this BritishStandard was carried out, consists of representatives from the following Government departments, and scientific and industrial organizations: Board of Trade British Steel Industry Chemical Industries Association* Fertiliser Manufacturers Association Ltd. Gas Cou
4、ncil Institution of Gas Engineers Ministry of Agriculture, Fisheries and Food Ministry of Health Ministry of Technology Laboratory of the Government Chemist* National Sulphuric Acid Association Royal Institute of Public Health withdraw the ampoule and invert it. Wipe the end that was immersed in the
5、 laboratory sample with a filter paper and seal rapidly. Weigh the ampoule again to the nearest0.5mg and determine to the nearest milligramme, by difference between the two weighings, the mass of test portion taken. Place the sealed ampoule in a250ml conical flask containing about50ml of water. Brea
6、k up the ampoule with a glass rod, shake, add0.5ml of phenolphthalein solution(3.2.2) and titrate with the sodium hydroxide solution(3.2.1). 3.4.2 For acids believed to contain less than 90%(m/m) of total acidity, expressed as formic acid. Place a test portion of1.5g to2.0g weighed to the nearest mi
7、lligramme, into a250ml conical flask containing about50ml of water. Add0.5ml of phenolphthalein solution(3.2.2) and titrate with the sodium hydroxide solution(3.2.1) to a faint pink end point. 3.5 Expression of results. Total acidity, expressed as formic acid(HCOOH), is given in per cent by mass by
8、the following formula: 4 Determination of acids other than formic acid 4.1 Field of application. This method is applicable to formic acid containing between0.5%and6.0%(m/m) of other acids calculated as acetic acid. 4.2 Principle. Titration with sodium hydroxide solution using a pH meter, of the acid
9、s remaining after quantitative oxidation of formic acid with excess mercuric oxide. 4.3 Reagents. Freshly boiled and cooled distilled water, or water of at least equal purity 1)should be used in the test. 4.3.1 Acetic acid, approximately0.5%(v/v) solution. Dilute5ml of glacial acetic acid to1000ml.
10、4.3.2 Mercuric oxide(red). 4.3.3 Sodium hydroxide, 0.1N standard volumetric solution(seeNote in3.2.1). 1) Attention is drawn to BS3978, “Water for laboratory use”. where V is the volume, in millilitres, of the N sodium hydroxide solution(3.2.1) used for the titration, A is the mass, in grammes, of f
11、ormic acid(HCOOH) corresponding to1ml of N sodium hydroxide solution (Theoretical value1ml=0.04603g of HCOOH; seeNote in3.2.1.) and E is the mass, in grammes, of test portion taken. VA E -100 BS4341:1968 2 BSI 12-1999 4.4 Apparatus. Normal laboratory apparatus together with: 4.4.1 Conical flasks, wi
12、th ground-glass necks, capacity250ml. 4.4.2 Reflux condenser, water cooled, with ground-glass joints to fit the flasks. 4.4.3 pH Meter with a glass electrode. 4.5 Procedure 4.5.1 Test portion a) For content of acids other than formic acid less than2%(m/m). Weigh5g of the laboratory sample(seeSection
13、2) to the nearest0.01g. b) For content of acids other than formic acid2%(m/m) and over. Weigh2g of the laboratory sample(seeSection2) to the nearest0.005g. 4.5.2 Blank test. At the same time as the analysis, carry out a blank test using the procedure described in4.5.3 and4.5.4 and the same quantitie
14、s of all reagents. 4.5.3 Preparation of test solution. Place the test portion(4.5.1) in one of the conical flasks(4.4.1). Add exactly5.0ml of acetic acid solution(4.3.1) and an amount of mercuric oxide(4.3.2) calculated on the basis of5.5g of mercuric oxide per gramme of formic acid present in the t
15、est portion. Then add sufficient water to bring the total volume to about30ml. Fit the flask with a condenser(4.4.2) and heat gently for10min. Fairly strong evolution of carbon dioxide from the solution containing the test portion occurs. Reflux gently for30min and rinse the condenser with20ml to25m
16、l of water. Cool the flask to room temperature and pour the contents without filtering into a250ml beaker. Rinse the flask into the beaker with20ml to25ml of water, and transfer the washings to the beaker. 4.5.4 Titration. Stir the solution vigorously, preferably using a magnetic stirrer, and keep s
17、tirring during the titration. Titrate the residual acids with the sodium hydroxide solution(4.3.3) using the pH meter(4.4.3). The end point of the titration is at pH8.6 for the test and at pH8.3 for the blank. Samples requiring more than10ml to15ml of the Sodium hydroxide solution(4.3.3) do not give
18、 a very sharp end point and a period of vigorous stirring is necessary in order to obtain a stable final pH. 4.6 Expression of results. The content of acids other than formic acid, expressed as acetic acid(CH 3 COOH), is given in per cent by mass by the following formula: 5 Limit test for inorganic
19、chlorides 5.1 Field of application. This method is applicable to samples in which the content of inorganic chloride, expressed as chlorine(Cl), is not greater than0.5%(m/m) and not less than0.0005%(m/m). If the inorganic chloride content is above or below that range, the method is applicable by redu
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