BS 576-2:1988 download free.Acetic acid for industrial use Part 2 : Methods of test for acetic acid.
1 Scope
This Part of BS 576 describes methods for testing acetic acid for industrial use.
NOTE The titles of the publications referred to in BS 576-2 are listed on the inside back cover.
2 Sampling and storage of sample
Take a representative sample from the bulk liquid.
NOTE Methods for sampling liquid chemical products are described in BS 5309.1 and BS 5309.3.
Store the laboratory sample in a clean, dry and airtight, ground glass stoppered bottle, or a screw-capped bottle fitted with a polyethylene cone insert, of such capacity that it is almost filled by the sample. Sufficient ullage should be left in the bottle to avoid excessive pressure changes that could arise from temperature variations during storage and handling. About 10 % ullage is recommended. If it is necessary to seal the bottle, take care to avoid any risk of contamination of the contents. Store the sample in a cool place in the dark.
3 Measurement of colour
Determine the colour by the method described in BS 5339.
4 Determination of crystallizing point
Determine the crystallizing point by the method described in BS 4633, using a thermometer no. A2OC/100 comp’ying with BS 593 in the inner tube.
NOTE A graph showing the relationship between crystallizing point and acetic acid content is given in Appendix B.
5 Determination of acetic acid content
5.1 Principle
A test portion of acetic acid is titrated with standard volumetric sodium hydroxide solution, using phenolphthalein as indicator. The acid content is then calculated, making allowance for any formic acid present.
5.2 Reagents
5.2.1 General. Use only reagents of recognized analytical grade, only methylated spirits complying with BS 3591, and only water complying with grade 3 of BS 3978.
5.2.2 Sodium hydroxide, standard volumetric solution, c(NaOH) = 1 mol/L,
5.2.3 Phenolphthalein, 5 gIL ethanolic solution. Dissolve 0.5 g of phenolphthalein in 100 mE of 95 % (VIV ethanol, or 95 % (V/14 industrial methylated spirits, and add 4 g/L sodium hydroxide solution until a pale pink coloration is obtained.
Add to each Nessler cylinder 1 mE of the silver nitrate solution (8.2.3) and mix. Allow the cylinders to stand in the dark for 5 mm and then compare the turbidity produced by the aliquot portion of the test solution with that produced by the standard turbidimetric solution (8.4.3).
8.5 Interpretation of results
The inorganic chlorides content does not exceed the limit of x % (rn/rn) of Cl if the turbidity produced by the test solution does not exceed that produced by the standard turbidimetric solution.
9 Limit test for inorganic suiphates
9.1 Principle
The turbidity obtained by adding a barium chloride solution to a test solution, acidified with hydrochloric acid, and the turbidity obtained from a sulphate solution, of known concentration, treated in the same manner are visually compared.
9.2 Reagents
9.2.1 General. Use only reagents of recognized analytical grade and only water complying with grade 3 of BS :3978.
9.2.2 Sodium carbonate, 53 gIL solution of the anhydrous salt.
9.2.3 Hydrochloric acid, 36.5 gIL solution of hydrogen chloride.
9.2.4 Barium, chloride dihydrate, 100 g/L solution.
9.2.5 Standard sulphate solution, containing 0.1 g of SO.12- per litre.
Transfer 20.8 mL of a standard volumetric sulphuric acid solution, c(112 H2S03) = 0.1 molfL, to a 1 000 mE one-mark volumetric flask. Dilute to the mark with water and mix.
1 mL of this solution contains 0.1 mg of SO42
9.3 Apparatus
Ordinary laboratory apparatus together with the following.
9.3.1 Filter papers, sulphate-free.
9.3.2 Two matched Nessier cylinders, graduated at 100 mE.
9.4 Procedure
9.4.1 Test portion. Weigh (M ± 0.01 M) g of the laboratory sample, where the value of Mdepends on the limit set for the inorganic suiphates content, y % (rn/rn), and is given in Table 3.
10.4.2 Preparation of the test solution. Transfer the test portion (10.4.1) quantitatively to a 250 mL one-mark volumetric flask containing about 50 mL of water. Dilute to the mark and mix.
10.4.3 Preparation of standard matching solution. Place 20 mL of water in one of the Nessler cylinders (10.3.1) and add 2.0 mL of the standard lead solution (10.2.4) and 1 mL of the ammonia solution (10.2.2). Dilute to the 50 mL mark with water and mix. Add 0.1 mL (two drops) of the sodium suiphide solution (10.2.3) and mix again.
10.4.4 Test. Transfer an aliquot portion of the test solution (10.4.2), as given in Table 4, to the second Nessler cylinder (10.3.1). Add the ammonia solution (10.2.2) until the solution is alkaline to the litmus paper (10.2.5) (blue colour), dilute to the 50 mL mark with water and mix. Add 0.1 mL (two drops) of the sodium suiphide solution (10.2.3) and mix again.
Compare the depth of colour of this solution with that of the standard matching solution (10.4.3).
10.5 Interpretation of results
The heavy metals content does not exceed the limit of z % (rn/rn), expressed as Pb, if the depth of colour produced by the test solution does not exceed that of the standard matching solution.
11 Determination of formic acid content
NOTE This method is applicable to products having formic acid contents between 0.02 % (rn/rn) and 0.35 % (rn/rn).
11.1 Principle
The total reducing matter in a test portion is determined by oxidation with an excess of sodium hypobromite solution and the excess sodium hypobromite is determined by iodometry.
The reducing compounds other than formic acid are determined in a further test portion by oxidation with an excess of potassium bromide-bromate solution, in an acid medium, and the excess potassium bromide-bromate is determined by iodometry.
The formic acid content is calculated from the difference between the two determinations.
11.2 Reactions
The following reactions occur during the test.
HCOOH + NaOBr — NaBr + CO2 + H90
NaOBr + 21(1 + 2HC1 — 2KC1 + NaBr + H20 + 19
KBrO3 + 5KBr + 6HCI —‘ 6KCI + 3Br2 + 3HO
3Br, + 6K! — 6K13r + 3J
2Na9S2O: + I., Na9S.1O + 2NaI
13.4 Apparatus
Ordinary laboratory apparatus together with the following.
13.4.1 Weighing pipette, of capacity 20 mL.
13.4.2 Distillation apparatus, as shown in Figure 2, with ground glass joints, consisting of the following items:
a) distillation flask, of capacity 250 mL, of borosilicate glass;
b) splash.head adapter with a recovery bend;
c) water condenser;
d) receiver adapter.
13.4.3 Gonical flask, of capacity 200 mL, graduated at 50 mLand lOOmL.
13.4.4 Burette, of capacity 50 mL. complying with class A of BS 846.
13.5 Procedure
13.5.1 Test portion. Using the weighing pipette (13.4.1), weigh, to the nearest 0.0001 g, approximately 10 mL of the laboratory sample.
13.5.2 Blank test. Carry out a blank test at the same time as the determination, following the same procedure (13.5.3). using the same amounts of all reagents [except the sodium thiosuiphate solution (13.3.5)1 as used for the determination, but omitting the test portion.
13.5.3 Determination. Transfer the test portion (13.5.1) to the distillation flask [13.4.2 a)] containing 100 mL of water. Add 2 g of the phosphoric acid solution (13.3.3) to the distillation flask and place 40 mL of water and 10.0 mL of the sodium hydrogen sulphite solution (13.3.2) in the conical flask (13.4.3). Assemble the apparatus as shown in Figure 2, partially immersing the conical flask in a bath containing a mixture of ice and water.
Heat the distillation flask so that its contents are gently boiling after a few minutes and then slowly distil about 50 mL of liquid into the conical flask. Remove the source of heat, disconnect the distillation flask and remove the bath of ice and water. Rinse the inner walls of the condenser and of the receiver adapter with water, collecting the washings in the conical flask and allow to stand at ambient temperature for 30 mm.
Add 30.0 mL of the iodine solution (13.3.4) to the conical flask and titrate the excess of iodine with the sodium thiosulphate solution (13.3.5), from the burette (13.4.4), to a pale yellow colour. Add 0.5 mL of the starch solution (13.3.6) and continue the titration until the blue colour is discharged.