Preparation and Standardization of 0.1M Ethanolic Sodium Hydroxide Solution SOP

1.0 Scope:

This procedure can be used to prepare and standardize 0.1 Molar Ethanolic sodium hydroxide solution.

2.0 Apparatus:

• 1000 ml volumetric flask
• 250 ml glass-stoppered conical flask
• 100 ml graduated burette
• 100 ml volumetric flask

3.0 Reagents:

• Sodium hydroxide AR grade
• Benzoic acid AR grade
• Thymolphthalein solution
• Ethanol (95%v/v)

Preparation of Reagents:

Thymolphthalein solution:

Dissolve approximately 0.1g of Thymolphthalein in ethanol (95%v/v) and make to 100ml. and store in a clear glass stoppered bottle.

4.0 Preparation of 0.1M Ethanolic Sodium Hydroxide Solution:

• Dissolve approximately 4.2 g of sodium hydroxide in 5 ml of purified water and add enough aldehyde-free ethanol to make up to 1000 ml.
• Allow the solution to stand in a tightly-stoppered bottle for 24 hours.
• Then quickly pour off the clear liquid into a cleaned and dried plastic bottle.

5.0 Standardization of 0.1M Ethanolic Sodium Hydroxide:

• Transfer about 0.6 g (accurately weighed) of the powdered and dried Benzoic acid (Dried at about 120 °C for 2 hours) to a 250 ml glass stoppered conical flask, dissolve in a mixture of 30 ml ethanol (95%) and 6 ml purified water.
• Take 0.2 ml of thymolphthalein solution as indicator and titrate with the ethanolic sodium hydroxide solution (0.1 M) until a permanent pink colour is obtained.

Each ml of 0.1M ethanolic sodium hydroxide is equivalent to 0.01221 g of C₇H₆O₂.

6.0 Molarity Calculation:

Where:
M = molarity of 0.1M ethanolic sodium hydroxide
W = weight of benzoic acid in g
V = volume of 0.1M ethanolic sodium hydroxide in ml

7.0 Storage:

Store in a transparent glass stoppered bottle

8.0 Reference:

As per IP –1996