BS ISO 125:2020 pdf download – Natural rubber latex concentrate — Determination of alkalinity.
5.2 Sulfuric acid, c(H 2 SO 4 ) = 0,05 mol/dm 3 , or hydrochloric acid, c(HCl) = 0,1 mol/dm 3 , standard volumetric solution. 5.2.1 Standardization of sulfuric acid, standardize 0,05 mol/dm 3 H 2 SO 4 by pipetting 10 cm 3 of 0,05 mol/dm 3 Na 2 CO 3 solution (5.5) into a flask and titrating with 0,05 mol/dm 3 H 2 SO 4 , using methyl orange (5.4) as indicator. 5.2.2 Standardization of hydrochloric acid, standardize 0,1 mol/dm 3 HCl by pipetting 10 cm 3 of 0,05 mol/dm3 Na 2 CO 3 solution (5.5) into a flask and titrating with 0,1 mol/dm 3 HCl, using methyl orange (5.4) as indicator. 5.3 Methyl red, 0,1 % solution in ethanol of minimum purity 95 % (by volume). 5.4 Methyl orange, 0,1 % solution in ethanol of minimum purity 95 % (by volume). 5.5 Sodium carbonate solution, c(Na 2 CO 3 ) = 0,05 mol/dm 3 . Dry the Na 2 CO 3 used to prepare this solution at 120 °C ± 5 °C for 2 h before preparing the solution. 6 Apparatus Standard laboratory equipment together with: 6.1 Electrical stirrer, with earthed (grounded) motor and non-metallic propeller-type blade, or magnetic stirrer. 6.2 pH-meter, equipped with a combined electrode suitable for use in solutions up to pH 12, as specified in ISO 976, and capable of being read to 0,02 pH-units. 6.3 Balance, capable of being read to 0,01 g. 7 Sampling Carry out sampling in accordance with one of the methods specified in ISO 123.
8 Procedure 8.1 General Carry out the determination in duplicate. Add, while stirring, 10 cm 3 of stabilizer solution (5.1) to about 200 cm 3 of water in a 400 cm 3 beaker. Weighing to the nearest 10 mg, add between 5 g and 10 g of the latex concentrate by difference from a weighing bottle and stir until thoroughly mixed. Ensure that the latex is added so that none runs down the side of the beaker (which could result in loss of ammonia) or down the side of the weighing bottle. Titrate the resulting mixture either by the method described in 8.2 or by that described in 8.3. 8.2 Potentiometric titration Insert the electrode of the pH-meter and, with continual stirring, add sulfuric acid or hydrochloric acid solution (5.2) from a burette, adding the acid drop by drop on approaching the end point of pH 6,0 ± 0,05.