- Distilled water
- NaOH (sodium hydroxide) pellets
- Analytical balance
- Volumetric flask (1000 mL)
- Graduated cylinder (1000 mL)
- Safety goggles
- Gloves
- Magnetic stirrer or stirring rod
Procedure:
Step 1: Preparation of NaOH Stock Solution (approximately 1N)
- Put on your safety goggles and gloves.
- Weigh approximately 4 g of NaOH pellets using an analytical balance.
- Transfer the weighed NaOH pellets into a 1000 mL volumetric flask.
- Add approximately 500 mL of distilled water to the flask.
- Swirl the flask gently to dissolve the NaOH pellets.
- Add additional distilled water until the volume reaches 1000 mL.
- Mix thoroughly to ensure a uniform NaOH solution.
Step 2: Standardization of NaOH Solution (to determine exact concentration)
- Pipette 20 mL of the prepared NaOH solution into a clean 250 mL Erlenmeyer flask using a calibrated pipette.
- Add 2 drops of phenolphthalein indicator to the flask.
- Fill a burette with a standardized hydrochloric acid (HCl) solution of known concentration (e.g. 0.1N HCl).
- Slowly add the HCl solution from the burette to the NaOH solution in the Erlenmeyer flask, swirling continuously.
- Note the initial and final burette readings.
Step 3: Calculation of Exact Concentration of NaOH Solution
- Calculate the volume of HCl used for the titration:
_Volume of HCl_ = _Final burette reading_ - _Initial burette reading_
- Calculate the exact concentration of the NaOH solution using the formula:
- _Exact concentration of NaOH_ (N) = ( Molarity/normality of HCl) * ( Volume of HCl in liters / volume of NaOH used)
Step 4: Adjustment of NaOH Solution to 0.1N
- Determine the difference between the exact concentration of NaOH solution obtained in Step 3 and the desired concentration (0.1N).
- Adjust the concentration by adding more distilled water or concentrated NaOH solution, as needed.
- Mix the solution thoroughly to ensure uniformity.
- Repeat Steps 2 and 3 to verify the exact concentration of the adjusted NaOH solution.
By following these steps, you can accurately prepare an exact 0.1N solution of NaOH for your laboratory experiments or titrations.
