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
20、cing or increasing the mass of sample taken(5.5.1). 5.2 Principle. Comparison of the turbidity, obtained by the addition of silver nitrate to a solution prepared from the test sample in presence of nitric acid, with that similarly obtained from a chloride solution of known concentration. 5.3 Reagent
21、s. Distilled water, or water of at least equal purity 2)should be used in the test. All reagents and filter paper should be chloride free. 5.3.1 Nitric acid, approximately5N solution. 5.3.2 Standard chloride solution containing0.1g/l of Cl . Place28.2ml of a0.1N hydrochloric acid solution in a1000ml
22、 one-mark volumetric flask. Dilute to the mark and mix thoroughly. 1ml of this standard solution contains0.0001g of Cl . 5.3.3 Silver nitrate, 50g/l solution. 5.4 Apparatus. Normal laboratory apparatus. 5.5 Procedure 5.5.1 Test portion. Weigh to the nearest0.5g,50g of the laboratory sample(seeSectio
23、n2). where V 1is the volume, in millilitres, of the0.1N sodium hydroxide solution(4.3.3) used for the titration of sample solution, V 2is the volume, in millilitres, of the0.1N sodium hydroxide solution(4.3.3) used for the titration of the blank, A is the mass, in grammes, of acetic acid(CH 3 COOH)
24、corresponding to1ml of0.1N sodium hydroxide solution, (theoretical value1ml=0.0060g of CH 3 COOH; seeNote in3.2.1) and E is the mass, in grammes, of the test portion. 2) Attention is drawn to BS3978, “Water for laboratory use”. V 1 V 2 ()A E -100 BS4341:1968 BSI 12-1999 3 5.5.2 Preparation of test s
25、olution. Transfer the test portion(5.5.1) to a250ml one-mark volumetric flask, dilute to the mark and mix thoroughly. If the solution is not clear, pass it through a filter paper. This should remove turbidity due to impurities such as aluminium. If there is turbidity in the filtrate due to contamina
26、tion with wax, remove it by shaking with a suitable solvent, for example, light petroleum. 5.5.3 Comparison of chloride content. Place1.0ml of standard chloride solution (5.3.2) into a100ml Nessler cylinder, dilute to the mark, add2ml of the nitric acid solution(5.3.1) and mix. For a sample required
27、 to contain not more than x%(m/m) of chloride expressed as Cl , transfer to a100ml Nessler cylinder an aliquot,0.05/x ml 3)of the test solution(5.5.2), dilute to the mark, add2ml of the nitric acid solution(5.3.1), and mix. Add to each Nessler cylinder1ml of silver nitrate solution(5.3.3) and mix. A
28、llow the cylinders to stand in the dark for5minutes, then compare the turbidities produced by the aliquot of the test solution with that produced by the standard chloride solution(5.3.2). 5.6 Expression of results. If the turbidity produced from the test solution is less than that produced from the
29、standard chloride solution, report that the sample contains less than x%of inorganic chloride expressed as Cl , otherwise report it as containing not less thanx %. 6 Limit test for inorganic sulphates 6.1 Field of application. This method is applicable where the sulphate content, expressed as SO 4 ,
30、 is not greater than0.1%and not less than0.001%(m/m). If the sulphate content is above or below that range, the method is applicable by reducing or increasing the mass of the test portion taken(6.5.1). 6.2 Principle. Comparison of the turbidity, obtained by the addition of barium chloride to a solut
31、ion prepared from the laboratory sample in presence of hydrochloric acid, with that similarly obtained from a sulphate solution of known concentration. 6.3 Reagents. Distilled water, or water of at least equal purity 4)should be used in the test. 6.3.1 Sodium carbonate, approximately N solution. 6.3
32、.2 Hydrochloric acid, approximately N solution. 6.3.3 Barium chloride, (BaCl 2 .2H 2 O)10g/l solution. 6.3.4 Standard sulphate solution containing 0.1g/l of SO 4 . Place20.8ml of0.1N standard volumetric solution of sulphuric acid in a1000ml one-mark volumetric flask. Dilute to the mark and mix thoro
33、ughly. 1ml of this solution contains0.0001g of SO 4 . 6.4 Apparatus. Normal laboratory apparatus. 6.5 Procedure 6.5.1 Test portion. Weigh to the nearest1g,1001g of the laboratory sample (seeSection2), into an evaporating basin. 6.5.2 Preparation of test solution. To the test portion(6.5.1), add0.2ml
34、 of the sodium carbonate solution(6.3.1) and evaporate to dryness on a boiling water bath. Dissolve the residue in water containing1ml of hydrochloric acid solution (6.3.2), transfer the solution to a250ml one-mark volumetric flask, dilute to the mark and mix. If the solution is not clear, pass it t
35、hrough a filter paper. This should remove turbidity due to impurities such as aluminium. If there is turbidity in the filtrate due to contamination with wax, remove it by shaking with a suitable solvent, for example light petroleum. 6.5.3 Comparison of sulphate contents. Place4.0ml of the standard s
36、ulphate solution(6.3.4) into a100ml Nessler cylinder, dilute to the mark, add2ml of the hydrochloric acid solution(6.3.2) and mix. For a sample required to contain not more thanx%(m/m) of inorganic sulphate expressed as SO 4 , transfer to a100ml Nessler cylinder an aliquot0.1/xml 5)of the test solut
37、ion(6.5.2), dilute to the mark, add2ml of the hydrochloric acid solution(6.3.2) and mix. Add to each Nessler cylinder2ml of barium chloride solution(6.3.3) and mix. Allow the cylinders to stand for5minutes, mix again and compare the turbidities produced by the aliquot of the test solution with that
38、produced by the sulphate solution of known concentration. 6.6 Expression of results. If the turbidity produced from the test solution is less than that produced from the sulphate solution of known concentration(6.5.3), report that the sample contains less than x % of inorganic sulphate expressed as
39、SO 4 , otherwise report it as containing not less than x %. 3) If the mass of the test portion(5.5.1) was reduced or increased (see5.1), adjust accordingly the numerator of this fraction. 4) Attention is drawn to BS3978, “Water for laboratory use”. 5) If the mass of the test portion(6.5.1) was reduced or increased(see6.1), adjust accordingly the numerator of this fraction.
