INDUSTRIAL AND ENGINEERING CHEMISTRY
4E6
yo so.
=
ml of iodate solution X normality X 3.203 -- weight of sample
Vol. 16. No. 8
Cnlculations. Weight of sample =
TOTALACIDITY. Weigh a dried platinum weighing bottle,
with cover, on a n analytical balance. (Type bottle as shown in Figure 3 may be used.) Transfer 7 to 8 ml. (7 to 8 ml. of the diluted acid will require between 75 and 95 ml. of N sodium hydroxide for titration) of the diluted acid sample with a Saran dropping pipet fitted with a rubber bulb a t the top. Cover the weighing bottle and reweigh. Transfer about 25 ml. of distilled water to a 200-ml. platinum dish. (A silver or Monel dish, or a 250-ml. glass beaker coated with wax, serves as an acceptable substitute.) Add 1 ml. of p h e n o l p h t h a l e i n indicator (0.i -0 phenolphthalein solution in denatured alcohol) and just enough N sodium hydroxide solution to give a pink color. (Only a fraction of a diop of N sodium hydroxide normally will be needed to produce a pink color.) Allow about 75 ml. of N sodium hydroxide solution to run from the chamber buret into the platinum dish. Immediately submerge the weighing bottle in the Dlatinum dish and loosen the cover. Stir, and titrate with N ~ i ~ platinum ~ ~ ~ sodium hydroxide to the first peFmaWeishins Bottle nent pink color of the indicator. Heat A~~~~~~~~~~ the solution to boiling and if the 22 grams color fades, add more sodium hydroxide to the firct permanent pink color. (If a wax-lined beaker is used, the solution must be transferred to an uncoated beaker befoce hcsting.) Calculations.
~-
Of
’%total acidity as H F =
weight of anhydrous HF -._____ weight of ice + weight of anhydrous HF
%,hydrofluosilieic acid = ml. of 0.1 N NaOH X normality X ~_ 0.036 X 100 weight of sample
F e Added Grams 72
HISiF6 Found Grams %
0.003 0.006 0.009 0.012 0.015
0.198 0.1S8 0.172 0.151 0.137 0.135
0.02 0.04 0.06 0.08 0.10
0.132 0.125 0 115 0.101 0.091 0,083
Error Caused by Iron, % EsSiFs 0.000
0.007
0.017 0 031 0.041 0 049
S ~ L F U RACID I C (Sulfuric Acid and Fluosulfonic Acid, Calculatcd as Sulfuric Acid). Weigh on a torsion bslance a 50.0gram aliquot of the sample into a 75-ml. platinum dish and evaporate to apparent dryness on a water bath. Add 10 ml. nf water and evaporate again to dryness on the water bath. Repeat, the evaporations with water until no odor of hydrofluorir acid is when hot, then add water and evaporate once more. 3detected . Usually two evaporations with water are sufficient for sulfuric wid rontents below 0.1 40. When all the hydrofluoric acid has been expellcd, add 25 ml of carbon dioxide-free water, 1 Pram of sodiurn fluoride. and 1 pram of potassium oxalate. Tkrate with 0.1 N alkali ‘using phenolphthalein indicator. The titration is equi-c-dent to sulfuric and fluosulfonic acid. Calculate as sulfuric acid and report to two significant figures. weight of sampie =
Weight of sample = weight
weight Of 'liquet
weight of anhvdrous HF weight of ice weight of anhydrous HE’
+
ml. of SaOH X normalitv x 0.02 weight of sample
x
100
HTDROFLL-OSILICIC ACID. Weigh 50 prarns of diluted hydrofluoric acid in a platinum beaker (dull fi:iish preferred) on a platform balance (i0.5-gram accuracy). Add 0.2 gram of sodium chloride and stir until the salt has dissolved. Place the beaker o n a steam bath and evaporate to dryness. Add 25 ml. of distilled water and stir until the solids have dissolved. Add 2 grams of potassium chloride and again stir until dissolved. Add 1ml. of phenolphthalein indicator. Place the beaker in a n ice bath and allow to cool for a t least 15 minutes. Carefully titrate the cold solution with silica-free N sodium hydroxide until the end point has nearly been reached. (If silica-free alkali is not readily available, the silica content of the alkali used may be determined and subtracted as a blank.) Complete the titration with 0.1 N silica-free sodium hydroxide to the first pink color that persists for a t least 15 seconds. Neglect the amount of alkali added to this point. ( I t is desirable to neutralize most of the acid fluorides with N alkali and to finish the neutralization with 0.1 N alkali as directed. If dilute sodium hydroxide is used for the entire neutralization, the large volume required dilutes the solution, and also raises its temperature. Both of these factors lead to a fading endpoint: some of the silica is hydrolyzed, and the results tend to be low.) Heat the solution to boiling and titrate with 0.1 N sodium hydroxide to a pink end point. Reheat to boiling and finish the titration of the hot solution to the first pink which persists for 45 seconds. With less than 0.1% of silica, this second heating is not necessary. Record the volume of sodium hydroxide used for the hot titration only, which is equivalent to the silica. (Ap,preciable quantities of iron interfere wit,h hydrofluosilicic acid determination, causing low values, as shown in the data table below. Present experience indicates the iron content of anhydrous hydrofluoric acid is generally less than O.Ol%, a s iron, on anhydrous hydrofluoric acid basis, even when the acid 1s shipped or stored in steel containtm. However, when iron content is 0.0270, or higher, a correction should be applied based upon the amount of iron present.)
weight of anhydrous HF weight of aliquot X -. weight of ice X weight of anhydrous H F
% (HzS04+ HSOIT) as H2SOI = ml. __ of 0.1 N NaOH
X normality X 0.049 X 100 weight of sample
Note. The sodium fluoride shouid be fluosilicate-free and neutral. I t is added to prevent-the hydrolysis of iron and aluminum salts. Potassium oxalate is added to fix salts of copper, pickel, leari, etc. Both these reagents may be omitted vhen the metal impurities are absent.
DETERMINATIOK O F WATER. For the alkVhtiOn grade O f anhydrous hydrofluoric acid, water is regarded as the difference. from loo’%, subtracting the assay and impurities LITERATURE CITED
(1) Lange, N. A . , “Handbook of Chemistry”, 4th ed., p. 997, Pandusky, Ohio, Handbook Publishers Co., 1938. (2) Manufacturing Chemists’ Association, Manual Sheet H-2 (adopted 1944). (3) Ibid., TC-5 (adopted 1943).
Physical Methods of Analysis of Synthetic and Natural Rubber-Correction In the article “Physical Methods of Analysis of Synthetic and Natural Rubber” [IND. ENC.CHEW,ANAL.ED., 16, 9 (194431 under the section “Dissolving Rubber Hydrocarbon and Separating If from Compounding Ingredients”, pagc 13. Method 11, the direct,ions should read: “Sheet the sample t o a thickness of approximately 0.0375 cm. (0.015 inch) on a tight cold 15 X 30 cm. (6 X 12) inch laboratory mill.” A. R . DAVIS
