MHS AP Chemistry
Titration of Vinegar

Vinegar is a dilute solution of acetic acid.  It is a monoprotic acid that can be represented as "HAc."  Vinegar is typically 5% by volume acetic acid, and 95% water.

Part 1 - Preparation

  1. Look up Ka for acetic acid in the appendix of your textbook.
  2. Look up the density of acetic acid in the Merck Index or the CRC handbook.
  3. Use the density of acetic acid to determine the molarity of a 5% solution in water.
  4. Choose a solution of sodium hydroxide that is closest in concentration to vinegar.  Prepare your base dispensing buret.
  5. Calibrate your pH meter using fresh buffer solutions.
  6. Standardize your base solution if necessary.
Part 2 - Titration
  1. Titrate a vinegar sample until the pH is about 13.  Keep a record of pH vs. total mL of base added.  You may be instructed to use an indicator and include observations.
  2. Repeat for three trials.  Make sure you have as many points as possible in the range where the pH changes fastest.
  3. Rinse each solution down the drain with excess water.
  4. Rinse your buret with clean water several times, and leave it upside down in the clamp with the valve open.
Part 3 - Analysis
  1. Graph the data from each trial on separate sheets.  Put mL of base on the x-axis and pH on the y-axis.  The graph should be landscape and fill the page.
  2. Use a ruler to draw a vertical line at the steepest part of each curve.
  3. [If chapter 17 started] Use this information to determine Ka for each sample.
  4. [If chapter 17 started] Calculate your average Ka and percent error from the accepted Ka.
  5. Use your graph to calculate the actual molarity of your sample, and compare it to your predicted molarity (part 1#3).
[Syllabus 17][MHS AP Chem page]