0.1 N Perchloric Acid(HClO4) preparation

 

Perchloric Acid, Tenth-Normal (0.1 N) (in Glacial Acetic Acid) HClO4,                                                            100.46

10.05 g in 1000 mL

NOTE—Where called for in the tests and assays, this volumetric solution is specified as “0.1 N perchloric acid.” Thus, where 0.1 N or other strength of this volumetric solution is specified, the solution in glacial acetic acid is to be used, unless the words “in dioxane” are stated. [See also Perchloric Acid, Tenth-Normal (0.1 N) in Dioxane.]

Mix 8.5 mL of perchloric acid with 500 mL of glacial acetic acid and 21 mL of acetic anhydride, cool, and add glacial acetic acid to make 1000 mL. Alternatively, the solution may be prepared as follows. Mix 11 mL of 60 percent perchloric acid with 500 mL of glacial acetic acid and 30 mL of acetic anhydride, cool, and add glacial acetic acid to make 1000 mL.

Allow the prepared solution to stand for 1 day for the excess acetic anhydride to be combined, and determine the water content by Method I (see Water Determination         921  ), except to use a test specimen of about 5 g of the 0.1 N perchloric acid that is expected to contain approximately 1 mg   of water and the Reagent (see Reagent under Method Ia in Water Determination   921  ) diluted such that 1 mL is equivalent to about 1 to 2 mg of water. If the water content exceeds 0.5%, add more acetic anhydride. If the solution contains no titratable water, add sufficient water to obtain a content of between 0.02% and 0.5% of water. Allow the solution to stand for 1 day, and again   titrate the water content. The solution so obtained contains between 0.02% and 0.5% of water, indicating freedom from acetic anhydride.

Standardize the solution as follows.

 

Accurately weigh about 700 mg of potassium biphthalate, previously crushed lightly and dried at

120      for 2 hours, and dissolve it in 50 mL of glacial acetic acid in a 250-mL flask. Add 2 drops of

 crystal violet TS, and titrate with the perchloric acid solution until the violet color changes to blue- green. Deduct the volume of the perchloric acid consumed by 50 mL of the glacial acetic acid.

Each 20.42 mg of potassium biphthalate is equivalent to 1 mL of 0.1 N perchloric acid.