pH 
791
—
Gently but thoroughly mix 10 mL with 0.3 mL of saturated potassium chloride solution in a 100-mL borosilicate volumetric flask. Dilute with carbon dioxide-free water having a pH of 7.0 ± 0.5 to volume. Completely purge the solution by vigorous nitrogen bubbling, and continue the bubbling during the pH measurement. Determine the pH potentiometrically when the reading stabilizes: it is between 6.0 and 7.5.
Assay—
Barium hydroxide solution—
Dissolve 75 g of barium hydroxide (octahydrate) in 1 L of water. Filter before using.
Procedure—
Flush a 250-mL iodine flask with nitrogen to expel the air, and insert the stopper in the flask to exclude carbon dioxide. Transfer 50.0 mL of Barium hydroxide solution and about 600 mg of Propylene Carbonate, accurately weighed, to the flask, and loosely reinsert the stopper. Moisten the stopper with 3 drops of water, and heat the flask on a steam bath for 10 minutes. Remove the flask from the steam bath, add 6 drops of phenolphthalein TS, and titrate while hot with 0.5 N hydrochloric acid VS until only a trace of pink color remains. Perform a blank determination, using the same Barium hydroxide solution. Each mL of 0.5 N hydrochloric acid consumed is equivalent to 25.52 mg of C4H6O3.
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