SCH 3U Acid-Base Titration

Determining the Concentration of Acetic Acid

in Commercial Vinegars

Purpose: To determine the concentration of acetic acid in an unknown sample of vinegar.

Vinegar is a dilute solution of acetic acid CH3COOH. Only the hydrogen atom that is attached to the oxygen atom is acidic. As a consumer, you can buy vinegar with different concentrations. To maintain consistency and quality, the manufacturers of vinegar need to determine the percent concentration of acetic acid in each batch of vinegar.

Procedure:

• Label a clean dry beaker for each of the following liquids: NaOH and distilled water.
• Obtain your vinegar sample from the teacher and record your sample number.
• Setup the burette and retort stand. Rinse the burette with water, and then with 10mL of the NaOH solution.
• Fill the burette with NaOH (make sure there are no air bubbles in the burette) and record the initial volume.
• Prepare your vinegar sample:
• Pipette 10mL of vinegar into your Erlenmeyer flask, and add 20mL of distilled water. Record the volume of vinegar in your table.
• Add 2-3 drops of phenolphthalein to the vinegar sample.
• Titrate the NaOH until a pale pink colour remains in the Erlenmeyer flask. A sheet of white paper under the flask will help you see the neutralization point.
• Record the final burette reading.
• Repeat the procedure with two more samples of vinegar:
• Trial 2: 15mL vinegar with 15mL distilled water
• Trial 3: 20mL vinegar with 10mL distilled water
• Calculate the percent by volume of acetic acid.

Observations:

Flask #