To 900 ml of glacial acetic acid add 8.5 ml of perchloric acid, mix, add 30 ml of acetic anhydride, dilute to 1000 ml with glacial acetic acid, mix and allow to stand for 24 hours.
Wigth accurately about dissolve 0.35 g of potassium hydrogen phthalate in 50 ml of anhydrous acetic acid, warming gently if necessary. Allow to cool protected from the air and titrate with the perchloric acid solution using 0.05 ml of crystal violet solution as indicator. Each ml of 0.1M perchloric acid VS is equivalent to 20.42 mg of C8H5KO4.
Perform a duplicate and calculate the molarity factor.(MF)
Note down the average value .
MF = W/ 0.02042 x V
V = Volume of perchloric acid consumed in ml.
W = Weight of potassium hydrogen phthalate in g.
Restandardise before use.
Store in amber bottle with well fitted suitable stoppers which prevents access to atmospheric carbon dioxide.
Discard the solution after 30 days.
For storage and labeling follow the general procedure.