Preparation and standardization 0.1 M Potassium Hydroxide BP volumetric solution
Dissolve 6 g of Potassium hydroxide (Equivalent to 100 % of KOH ) in carbon dioxide free water and dilute to 1000 mL with the same solvent.
Dissolve 0.150 g of Potassium hydrogen phthalate RV in 50 mL of water. Titrate with the Potassium hydroxide solution, determining the end point potentiometrically or using 0.1 mL of Phenolphthalein solution as indicator.
1 mL of 0.1 M Potassium hydroxide is equivalent to 20.42 mg of C8H5KO4.
Molarity (M) = [0.1 x Weight of C8H5KO4 (in g)]/ [0.02042 x Titration reading (in mL)]
Limit: 0.1 M ± 5 % (0.0950 M – 0.1050 M)
3. PREPARATION OF INDICATORS / REAGENTS:
a. Phenolphthalein solution:
Dissolve 0.1 g of Phenolphthalein in 80 mL of Ethanol (96 %) 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).
4. STORAGE CONDITION:
Store in glass-stoppered bottles.