Preparation and standardization of 0.5 N Sodium Hydroxide USP Volumetric Solution
Dissolve 81 g of Sodium hydroxide in 150 ml of carbon dioxide free water, cool the solution to room temperature, and filter through hardened filter paper. Transfer 54.5 ml of the clear filtrate to a tight, polyolefin container, and dilute with carbon dioxide free water to 1000 ml.
Accurately weigh about 2.5 g of Potassium biphathalate, previously crushed lightly and dried at 120°C for 2 hours, and dissolve in 75 ml of carbon dioxide free water. Add 2 drops of Phenolphthalein TS, and titrate with the Sodium hydroxide solution to the production of a permanent pink colour.
Each 204.22 mg of Potassium biphthalate is equivalent to 1 ml of 1 N Sodium hydroxide.
Normality (N) = [Weight of KHC8H4O4 (in g)]/[ 0.20422 x Titration reading (in ml)]
Limit: 0.5 N ± 5 % (0.4750 N – 0.5250 N)
3. PREPARATION OF INDICATORS / REAGENTS :
a. Phenolphthalein TS:
Dissolve 1 g of Phenolphthalein in 100 ml of alcohol.
4. STORAGE CONDITION:
Store in glass stoppered bottles.