Sodium hydroxide (NaOH) is a commonly used reagent in chemistry and analytical laboratories. Here’s how to prepare and standardize both molar (1.0 M) and normal (1.0 N) sodium hydroxide solutions.
Preparation of 1.0 M Sodium Hydroxide Solution:
A 1.0 M sodium hydroxide solution contains one mole of NaOH in one liter of solution.
Materials Required:
– Sodium hydroxide pellets (NaOH)
– Distilled water
– A balance
– A glass stirring rod
– A glass or plastic container
– A 1.0 L volumetric flask
Procedure:
1. Weigh the sodium hydroxide pellets (40.00 g/mol) to make a 1.0 M solution. To prepare 1.0 L of 1.0 M solution, you’ll need 40.00 grams of NaOH. Ensure that the substance is accurately weighed.
2. Transfer the weighed NaOH into a clean, dry glass or plastic container.
3. Add distilled water to the container and stir the mixture with a glass stirring rod until the NaOH completely dissolves. The final volume of the solution should be less than 1.0 L at this stage.
4. Transfer the solution into a 1.0 L volumetric flask. Rinse the container with distilled water to transfer all NaOH to the flask.
5. Fill the volumetric flask to the 1.0 L mark with distilled water while maintaining the temperature at a consistent level (usually 20°C). The solution is now a 1.0 M sodium hydroxide solution.
Standardization of 1.0 M Sodium Hydroxide Solution to Prepare 1.0 N Solution:
To standardize the 1.0 M sodium hydroxide solution and prepare a 1.0 N solution, you’ll need to determine its exact molar concentration.
Materials Required:
– Potassium hydrogen phthalate (KHP, C8H5KO4)
– Phenolphthalein indicator
– A burette
– A balance
– A 1.0 L volumetric flask
Procedure:
1. Weigh out a sample of KHP of known purity. Accurately weighs about 20.04 grams of KHP. The molar mass of KHP is 204.22 g/mol.
2. Dissolve the weighed KHP in distilled water and transfer it into a 1.0 L volumetric flask.
3. Add a few drops of phenolphthalein indicator to the KHP solution. Phenolphthalein will turn the solution pink at the endpoint of the titration.
4. Prepare the burette with the 1.0 M NaOH solution.
5. Titrate the KHP solution with NaOH until the pink color disappears, indicating that the acid has been completely neutralized.
6. Record the volume of NaOH solution used for the titration. Use this volume to calculate the exact molar concentration of the NaOH solution.
7. If the calculated molarity is close to 1.0 M, the solution can be considered a 1.0 N sodium hydroxide solution. If not, adjust the concentration and re-standardize if necessary.
