Preparation and standardization of 0.5 N Potassium Hydroxide, Alcoholic USP Volumetric Solution
Dissolve about 34 g of Potassium hydroxide in 20 ml of water, and add aldehyde-free alcohol to make 1000 ml. Allow the solution to stand in a tightly stoppered bottle for 24 hours. Then quickly decant the clear supernatant into a suitable, tight container.
Accurately measure about 25 ml of 0.5 N Hydrochloric acid VS. Dilute with 50ml of water, add 2 drops of Phenolphthalein TS, and titrate with the alcoholic Potassium hydroxide solution until a permanent, pale pink colour is produced.
Normality (N) = [Volume of HCl (in ml) x Normality of HCl]/ [Titration reading (in ml)]
Limit: 0.5 N ± 5 % (0.4750 N – 0.5250 N)
3. PREPARATION OF INDICATORS / REAGENTS:
a. 0.5 N Hydrochloric acid:
Preparation and standardization as per respective procedure.
b. Phenolphthalein TS:
Dissolve 1 g of Phenolphthalein in 100 ml of alcohol.
c. Aldehyde-free alcohol:
Dissolve 2.5 g of Lead acetate in 5 ml of water, add the solution to 1000 ml of alcohol contained in a glass stoppered bottle, and mix. Dissolve 5 g of Potassium hydroxide in 25 ml of warm alcohol, cool the solution, and add it slowly, without stirring, to the alcohol solution of Lead acetate. After 1 hour shake the mixture vigorously, allow it to stand overnight, decant the clear liquid, and recover the alcohol by distillation.
4. STORAGE CONDITION:
Store in tightly stoppered bottles, protected from light.