BS EN 938:2009 pdf free download – Chemical ls used for treatment of water intended for human consumption一Sodium chlorite.
Dissolve 24,8 g of Na2S2O3.5H20 in water. Add 0,5 ml of chloroform as preservative, dilute to volume with water in a 1 000 ml one-mark volumetric flask and mix thoroughly.
To standardize: Weigh, to the nearest 0,1 mg, (160 ± 10) mg (m)of primary standard potassium dichromate into a tared glass beaker. Place the contents of the beaker in a 500 ml stoppered conical flask, add 100 ml of water and (2 ± 0,5) g of potassium iodide and stir to dissolve. Add (15 ± 1) ml of hydrochloric acid solution (diluted 1 + 1 by volume), swirl, and allow to stand for 5 mm. Titrate with the sodium thiosulfate solution until the solution is pale yellow. Add (5 ± 1) ml of starch solution 1 %(mass fraction) and titrate to the end point, i.e. to the disappearance of the blue-black colour. Record the volume (V) used.
The concentration, c, of the sodium thiosulfate standard volumetric solution (Na2S2O3.5H20), expressed in moles per litre is given by the following equation:
V is the volume, in millilitres, of the sodium thiosulfate standard volumetric solution used.
5.2.1.3.4 Potassium iodid
5.2.1.4 Apparatus
5.2.1.4.1 Ordinary laboratory apparatus and glassware with together the following:
5.2.1.4.2 Automatic potentiometric titrimeter.
5.2.1.4.3 Automatic burette, 10 ml, equipped with an injection tip.
5.2.1.4.4 Electromechanical stirrer.
5.2.1.4.5 Glass titration beaker, 400 ml.
5.2.1.4.6 Platinum —Silver/Silver-chloride combination electrode with a porous plug electrolytic junction.
5.2.1.5 Procedure
5.2.1.5.1 Test solution
Weigh, to the nearest 0,1 mg, a test portion (m) between 0,11 g and 0,15 g the laboratory sample.
5.2.1.5.2 Determination
Transfer the test solution (5.2.1.5.1) to a 400 ml titration beaker with 300 ml of water and 4 g of potassium iodide (5.2.1.3.4) and add, with stirring, 20 ml of H2S04 (5.2.1.3.2).
Input the calculation data in the titration microprocessor in accordance with the instruction manual.
Introduce the electrode into the titration beaker and titrate with the sodium thiosulfate standard volumetric solution (5.2.1.3.3).
5.2.2 Impurities
5.2.2.1 Determination of sodium chlorate content (NaCIO3)
5.2.2.1.1 General
This method is used to determine the chlorate content, in the range between 3,75 g/l and 15 g/l, in sodium
chlorite solutions for commercial use; it is specific for these species.
5.2.2.1.2 Principle
Direct determination of chlorate ion in a diluted solution of sodium chlorite by separation and chemical suppressed conductimetric detection (ionic chromatography).
NOTE Calibration is linear for concentration of chlorate ion between 3,75 mg/I and 15 mg/I in the diluted solution.
5.2.2.1.3 Reagents
5.2.2.1.3.1 All reagents shall be of a recognized analytical grade and the water used shall conform to grade 3 in accordance with EN ISO 3696.
5.2.2.1.3.2 Sodium carbonate and sodium hydrogen carbonate, eluant solution:
Mix one volume of sodium carbonate c(Na2CO3) = 2 mol/l with one volume of sodium hydrogen carbonate c(NaHCO3) = 0,75 mol/l.
5.2.2.1.3.3 Sulfuric acid solution c(H2SO4) = 0,025 mol/l regenerant solution.
5.2.2.1.3.4 Helium gas, high purity, for degassing eluant and regenerant solutions.
5.2.2.1.3.5 Water, ultra pure, conductivity 0,056 iS/cm.
5.2.2.1.3.6 Sodium chlorate stock solution at 1 g/l:
Weigh, to the nearest 0,000 1 g, 0,255 1 g of NaCIO3. Dissolve in 200 ml of the ultrapure water (5.2.2.1.3.5).