Experiment 10: Acid-Base Titrations - Ethanoic Acid in Vinegar

Background

• Vinegar contains 4-5% ethanoic acid (CH3COOH).
• This experiment determines the ethanoic acid content in vinegar through titration.
• The process involves diluting a vinegar sample and titrating it with a standardized 0.100 mol/L sodium hydroxide (NaOH) solution.
• Phenolphthalein is used as an indicator to determine the endpoint of the reaction.
• The chemical reaction is: CH3COOH(aq) + OH^-(aq) \rightarrow H2O(l) + CH3COO^-(aq)

Pre-Lab Work

• Review Module 9 in the Study Guide and Module 9 Lecture ppt slides on Canvas.
• Watch the following videos:
  • Video 1: Indicators
  • Video 2: Introduction to Titration
  • Video 3: Titration Calculations: Strong Acid - Strong Base
  • Video 4: Acid and Base Concentrations - Concept
  • Video 5: How to read a Burette
  • Video 6: RACI Titration Competition Videos

Learning Outcomes

• Laboratory safety (safe handling of chemicals, personal protective equipment)
• Prepare standard solution of particular concentration.
• Develop skills in using glass pipette and performing titration.
• Perform titration calculations.

Safety Notes

• NaOH is a base; handle with care to avoid spillage. Wash hands thoroughly after handling.
• Do not force the pipette into the pipette filler to prevent shattering and subsequent lacerations.
• When filling the burette, place it on the ground with a stand.

Procedure

• Watch the video on determining the concentration of ethanoic acid in commercial vinegar.

Identify Indicator Colors

• Place one drop of vinegar and one drop of sodium hydroxide on a piece of paper towel, ensuring the drops do not touch.
• Add a drop of phenolphthalein indicator solution to each spot and note the colors.

Dilution of Original Vinegar Solution

• Record the code number of your vinegar solution.
• Using a pipette, measure 25.00 mL of vinegar into a 250.00 mL volumetric flask.
• Add deionized water to make the solution up to 250.00 mL and mix thoroughly.

Titration of the Diluted Vinegar Solution

• Rinse the burette with 0.100 mol/L NaOH solution, then fill the burette. Record the initial reading.
• Use a glass pipette to measure out a 25.00 mL sample of diluted vinegar into a clean conical flask.
• Place 3 drops of phenolphthalein indicator into the flask.
• Slowly add the NaOH solution from the burette until one drop gives the required color change, indicating the endpoint of the titration.
• Record the final reading on the burette.
• Determine the volume of NaOH added by calculating the difference between the initial and final burette readings.
• Repeat the titration using a fresh sample of diluted vinegar and a clean conical flask each time until you have at least two titration volumes within 0.1 mL.