Preparation and standardization 0.1 M Potassium hydroxide EP of volumetric solution
1. PREPARATION:
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.
2. STANDARDISATION:
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.
1mL of 0.1 M Potassium hydroxide is equivalent to 20.42 mg of C8H5KO4.
Calculation:
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.