Sodium hydroxide volumetric solution is a common solution that is used in the pharmaceutical industry. It is an acid-base titration. Here we will see the preparation and standardization of sodium hydroxide volumetric solution as per USP.
Preparation And Standardization Of Sodium Hydroxide Volumetric Solution As Per USP:
Reagents Used in Preparation and standardization of sodium hydroxide volumetric solution:
- 95% Alcohol
- Phenolphthalein solution
- Carbon Dioxide free water
1. Preparation of 95 % Alcohol:
Mix 95 mL of absolute alcohol with 5 mL of water.
2. Phenolphthalein Solution:
Dissolve 1.0 gm of phenolphthalein in 100 mL of alcohol (95%)
3. Carbon Dioxide Free Water:
Water that has been boiled vigorously for a 5 min or more and allowed to cool protected from the absorption of carbon dioxide from the atmosphere or purified water that has a resistivity of NLT 18 Mohm-cm.
Preparation of 1N Sodium Hydroxide:
Dissolve 162 gm of sodium hydroxide in 150 mL of carbon dioxide free water, cool the solution to attain room temperature. Transfer 54.5 mL of above solution to 1000 mL of water.
Preparation of 0.1N Sodium Hydroxide:
Preparation of 0.1N sodium hydroxide and other strength are mentioned in the below table:
| Serial No. | Quantity of Sodium Hydroxide to be taken (in gm) | Strength of Volumetric Solution |
| 1 | 81 | 0.5N |
| 2 | 16.2 | 0.1N |
| 3 | 48.6 | 0.3N |
| 4 | 32.4 | 0.2N |
| 5 | 3.24 | 0.02N |
| 6 | 1.62 | 0.01N |
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Standardization of 1N Sodium Hydroxide:
Weigh accurately about 5gm of potassium biphthalate (Potassium Hydrogen phthalate), previously dried at 120°C for 2 hrs. and dissolve in 75 mL of carbon dioxide-free water.
likewise as per requirement by following the above table, weight for different strength volumetric solutions can be taken.
Titration of Sodium Hydroxide volumetric solution:
Titration can be perform by two ways 1. Manual titration and 2. Potentiometric Titration.
Manual Titration:
Add 2 drops of phenolphthalein solution and titrate with the 1N sodium hydroxide solution till permanent pink color appears.
Potentiometric Titration:
Titrate with the 1N sodium hydroxide solution, determine the endpoint potentiometrically using a combined pH glass electrode.
Note: Each 204.23mg potassium biphthalate is equivalent to 1 mL of 1N sodium hydroxide.
Weight of potassium biphthalate tobe taken for lower strength is given in below table: (As per USP)
| Serial No. | Quantity of potassium hydrogen phthalate to be taken (in gm) | Water (in mL) | Strength of Volumetric solution |
| 1 | 2.5 | 75 | 0.5N |
| 2 | 0.5 | 75 | 0.1N |
| 3 | 0.1 | 75 | 0.01N |
| 4 | 1.5 | 75 | 0.3N |
| 5 | 1 | 75 | 0.2N |
| 6 | 0.2 | 50 | 0.02N |
| 7 | 0.125 | 75 | 0.025N |
Calculation of sodium hydroxide volumetric solution:
Normality of Sodium Hydroxide = W/0.20422xV
Where, W= Weight of potassium biphthalate in g,
V= Volume of sodium hydroxide consumed in mL.
Important: Here, Benzoic acid also can be used for standardization of sodium hydroxide solution.
Take 200 mg benzoic acid in 100 mL of carbon dioxide-free water and perform as mentioned above procedure. But in such a case calculation formula will be different.
N= W/122.1xV
where, W= weight of benzoic acid in mg and,
V= Volume of sodium hydroxide consumed in mL
Storage of sodium hydroxide solution:
Protect from light and moisture. Solution should be stored in polyethylene container.
Incase of alcoholic solution, store in amber color glass-stoppered bottle.
Conclusion for preparation and standardization of sodium hydroxide volumetric solution:
In this article, you got an idea of how to do preparation and standardization of sodium hydroxide volumetric solution as per USP. Calculation of sodium hydroxide solution.
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