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D2896_11

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Calculate the quantity of sample required from its expected base number, BN, as follows. Approximate weight of sample, grams, g, equals 28 divided by the expected base number. For the back titration procedure, see 16.2 of the written standard. Or, when analyzing used oils, it may be necessary to use a smaller sample weight. Weigh the sample into the titration beaker, applying the limits shown as follows. A maximum of 20 grams should be taken for analysis. Add 120 milliliters of titration solvent to the sample. Place the beaker on the titration stand and stir the solution until the sample is dissolved. If solution of the sample proves difficult, dissolve it in 80 milliliters of chlorobenzene in the titration beaker. Then add 40 milliliters of glacial acetic acid. Many used oils contain some solid materials that will not dissolve. This is a frequently observed condition. Prepare the electrodes as directed in 10.1, 10.2, and 10.3 of the written standard. Position the electrodes in the solution so that they are immersed as far as possible. Continue stirring throughout the determination at a rate sufficient to produce vigorous agitation without spattering and without stirring air into the solution. Adjust the meter so that it reads in the upper part of the millivolt scale-- for example, 700 millivolts. For simple meters without this adjustment, it is necessary to incorporate a source of potential in series with the electrode. A 1.5-volt dry cell and potential divider is suitable. Fill the buret with 0.1N, normal, perchloric acid solution and place the buret in position in the titration assembly, taking care that the tip is immersed below the level of the surface of the liquid in the beaker. Record the initial buret and meter cell potential readings. Add suitable small portions of titrant and, after waiting until a constant potential has been established-- note 12 of the written standard-- record the buret and meter readings. At the start of the titration and in any subsequent regions, inflections, where 0.1 milliliters of titrant consistently produces a total change of more than 0.03 volts corresponding to 0.5 pH scale unit in the cell potential, add 0.05 milliliters portions in the intermediate region's plateaus, where 0.1-milliliter increments change the potential by less than 0.03 volts. Add large portions sufficient to produce a total potential change approximately equal to but not greater than 0.03 volts. Titrate in this manner until the potential changes less than 0.005 volts, corresponding to 0.1 pH scale unit per 0.1 milliliters. Consider the cell potential constant when it changes less than 0.005 volts per minute. Adjust the instrument in accordance with the manufacturer's instructions and set the titration speed at 1.0 milliliters per minute maximum. On completion of the titration, remove the beaker and rinse the electrodes and buret tip with titration solvent, then with water, then again with titration solvent. See 10.3 of the written standard. Store in water when not in use. See 10.1 of the written standard. For each set of samples, make a blank titration using 120 milliliters of titration solvent. For a manual titration, add 0.1 normal perchloric acid solution in 0.05 milliliter increments, waiting between each addition until a constant cell potential is established. Record meter and buret readings after each increment. Follow the procedure in 11.6.2 of the written standard for an automatic titration.

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Duration: 5 minutes and 34 seconds
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Language: English
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Posted by: abuckmaster on Sep 14, 2018

D2896_11

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