BS ISO 685-2020 pdf free download.Analysis of soaps — Determination of total alkali content and total fatty matter content
8.2 Test portion Weigh, to the nearest 0,001 g, about 5 g of the laboratory sample into the beaker (6.1).
8.3 Determination
8.3.1 General Dissolve the test portion (8.2) in about 100 ml of hot water. Pour the solution into one of the separating funnels (6.2) or into the extraction cylinder (6.3) and wash the beaker with small quantities of water, adding the washings to the separating funnel or to the extraction cylinder. Add a few drops of the methyl orange solution (5.7) and then, from a burette, add, while vigorously shaking the separating funnel or the extraction cylinder, an accurately measured known volume of the sulphuric acid solution (5.4) until there is an excess of about 10 ml. Cool the contents of the separating funnel or of the extraction cylinder to about 25 °C and add 100 ml of the light petroleum (5.2). Insert the stopper and gently invert the separating funnel or the extraction cylinder, while maintaining a hold on the stopper.
Open the stopcock of the separating funnel or the stopper of the extraction cylinder gradually to release any pressure, then close, gently shake and again release the pressure. Repeat the shaking until the water phase is clearly separated from the organic phase (if the two‑phase layer is not obvious, the emulsification can be broken by adding ethanol that does not exceed the volume of the water phase), and then allow to stand.
a) In the case of use of separating funnels Run off the aqueous layer into a second separating funnel (6.2) and extract with 50 ml of the light petroleum (5.2). Repeat the process, collect the aqueous layer in a conical flask and combine the three light petroleum extracts in the first separating funnel.
b) In the case of use of an extraction cylinder Using a siphon, draw off the light petroleum layer completely as possible into a separating funnel (6.2). Repeat the extraction twice with 50 ml of the light petroleum (5.2), combine the three light petroleum extracts in the separating funnel, transfer the aqueous layer as completely as possible to a conical flask and wash the extraction cylinder with small quantities of water, adding the washings to the conical flask.
Wash the light petroleum extract by shaking with water (about 25 ml) until the washings are neutral to the methyl orange solution (5.7). Usually three washings are sufficient. Allow each wash to stand for at least 5 min or such a time as is required to give a clear line of demarcation between the layers, before running off the aqueous layer. After the final washing has been run off, impart a swirling motion to the contents of the separating funnel by rotating it sharply, but without inverting it, to remove any water droplets adhering to the sides. Allow to stand for at least 5 min and run off any separated water. Collect the washings of the light petroleum extract quantitatively in the conical flask already containing the aqueous layer.
8.3.2 Determination of total alkali content Titrate the mixed acid aqueous layer and washings with the sodium hydroxide solution (5.5) using the methyl orange solution (5.7) as indicator. If the soap colour interferes with the methyl orange end‑point, a pH meter can be used to indicate the end‑point (pH value 3,1 to 4,4, maintain 10 s) during titration.
8.3.3 Determination of total fatty matter content Carefully transfer the washed light petroleum solution to a weighed, flat-bottomed flask, filtering if necessary through a dry filter paper. Wash the separating funnel with two or three small quantities of the light petroleum and filter the washings into the flask, taking precautions to prevent evaporation of the light petroleum during the filtration. Thoroughly wash the filter with the light petroleum, collecting the washings in the flask.
Evaporate off nearly all the light petroleum on the water bath (6.4), taking all necessary precautions, and under a slow stream of cold dry nitrogen or air. Dissolve the residue in 20 ml of the ethanol (5.3), add a few drops of the phenolphthalein solution (5.8) and titrate with the ethanolic potassium hydroxide solution (5.6) to a faint permanent pink colour. Note the volume used.
Evaporate the ethanolic solution on the water bath (6.4). When the evaporation is near completion, rotate the flask in order to distribute the potassium soap in a thin layer on the sides and bottom of the vessel. Carry out a preliminary drying of the potassium soap by adding acetone (5.1) and evaporating off the acetone on the water bath under a slow stream of cold dry nitrogen or air. Then heat to constant mass in the oven (6.5), controlled at (103 ± 2) °C, i.e. until the difference in mass after heating for an additional 15 min does not exceed 3 mg. Cool in a desiccator and weigh.BS ISO 685 pdf download.