Potentiometric Acid-Base Titration:
The tasks to be performed in Experiment #6 include:
A. Preparation of a 0.05 M solution of sodium hydroxide (titrant solution).
B. Standardization of the titrant solution.
C. Calibration of the pH-meter.
D. Determination of 2-acetoxybenzoic acid in aspirin tablets.
E. Determination of acetic acid in vinegar.
Could you suggest a potentiometric method for any of the analytes encountered thus far in our
experiments? Provide a short outline of the suggested procedure. ????
Sure! One potentiometric method that can be used for the determination of acetic acid in vinegar is acid-base titration using a pH electrode.
Outline of the suggested procedure:
1. Preparation of standard sodium hydroxide solution:
- Dissolve an accurately weighed quantity of sodium hydroxide pellets in distilled water.
- Transfer the solution to a volumetric flask and dilute to the desired concentration (0.05 M in this case).
2. Standardization of the titrant solution:
- Take a measured volume of the prepared sodium hydroxide solution (e.g., 25 mL) in a beaker.
- Add a few drops of phenolphthalein indicator to the beaker.
- Titrate the sodium hydroxide solution with a standardized solution of hydrochloric acid (0.1 M) until a color change is observed (from pink to colorless).
- Record the volume of hydrochloric acid required for neutralization.
- Repeat the titration 2-3 times to ensure accuracy and calculate the average volume of hydrochloric acid used.
- Use this volume to calculate the exact concentration of the sodium hydroxide solution.
3. Calibration of the pH-meter:
- Immerse the pH electrode in buffer solutions of known pH values (e.g., pH 4, 7, and 10).
- Adjust the readings on the pH-meter to match the known pH values of the buffer solutions.
- This calibration step ensures accurate pH measurements during the titration.
4. Determination of acetic acid in vinegar:
- Measure an aliquot of vinegar solution (e.g., 10 mL) using a volumetric pipette and transfer it to a titration flask.
- Add a few drops of an appropriate indicator, such as phenolphthalein or methyl orange.
- Titrate the acetic acid solution with the standardized sodium hydroxide solution while monitoring the pH using the calibrated pH-meter.
- Record the volume of sodium hydroxide solution required for neutralization and pH readings at regular intervals.
- The equivalence point of the titration is reached when the pH stops changing significantly.
- Calculate the concentration of acetic acid in the vinegar using the volume and concentration of sodium hydroxide, as well as the stoichiometry of the reaction between acetic acid and sodium hydroxide.
Note: It is important to rinse the pH electrode with distilled water between measurements and ensure proper handling and maintenance of the electrode for accurate results.