Preparation and standardization of 0.5 N Potassium Hydroxide, Alcoholic USP Volumetric Solution

1.  PREPARATION:

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.

2. STANDARDISATION:

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.

Calculation:

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.