Preparation and standardization of 0.5 M Potassium hydroxide (Alcoholic) EP Volumetric Solution
Dissolve 3 g of Potassium hydroxide in 5 mL of water and dilute to 100 mL with aldehyde-free alcohol.
Dissolve 0.500 g of Benzoic acid in 10 mL of water and 40 mL of Ethanol (96 per cent). Titrate with the Potassium hydroxide solution, determining the end point potentiometrically or using 0.1 mL of Phenolphthalein solution as indicator.
1 mL of 0.5 M Alcoholic Potassium hydroxide is equivalent to 61.06 mg of C7H6O2
Molarity = [0.5 x wt. of Benzoic acid in g]/ [Titration Reading x 0.06106]
Limit: 0.5 M ± 5 % (0.4750 M – 0.5250 M)
3. PREPARATION OF INDICATORS / REAGENTS:
a. Phenolphthalein solution:
Dissolve 0.1 g of Phenolphthalein in 80 mL of Alcohol and dilute to 100 mL with water.
Test for sensitivity: To 0.1 mL of the Phenolphthalein solution add 100 mL of carbon dioxide free water. The solution is colourless. Not more than 0.2 mL of 0.02 M Sodium hydroxide is required to change the colour to pink.
Colour change: pH 8.2 (colourless) to pH 10.0 (red).
c. 0.02 M Sodium hydroxide:
Dissolve 0.84 g of Sodium hydroxide in carbon dioxide free water and dilute to 1000 mL with the same solvent.
4. STORAGE CONDITION:
Store in glass stoppered bottles.