Chemistry
Name_______________________ Hour___
Titration of Vinegar
Introduction:
An acid base titration is a method used to determine an unknown molarity of acid or base. In this lab we will use
titration to determine the concentration of household vinegar, acetic acid (HC 2H3O2). When acids and bases are
mixed together, they react to form a salt and water. This is known as neutralization. When the moles of OH- ions
equal to the moles of H+ ions, the solution is said to be neutral. In this lab, you will titrate household vinegar with a
known concentration of NaOH in order to calculate the molarity of the vinegar (acetic acid).
Materials:
50 mL buret
1 erlenmeyer flask
1.0 M NaOH
household vinegar
phenolphthalein indicator
Procedure:
1. Prepare a base buret by rinsing once with distilled water and once with a small amount of
NaOH before filling the buret with NaOH. Be sure to remove all bubbles from the buret.
2. Measure 20.0 mL of acetic acid in a graduated cylinder. Transfer to an erlenmeyer flask.
3. Add two drops of phenolphthalein into your erlenmeyer flask.
4. Record the initial volume of your base buret in the data table.
5. Titrate with 1.0 M NaOH until a light pink endpoint is reached and remains for 20
seconds.
6. Record the final volume of the sodium hydroxide. Read all volume measurements to the
nearest 0.01 mL.
7. Repeat steps 1-6 for two more trials.
8. Leave the buret prepared for the next class. Last period should rinse burets with water
and leave upside down and open to dry out.
Data
Trial 1
Trial 2
Trial 3
Acetic Acid
Volume
____________________________________________
1.0 M NaOH Base
final volume
____________________________________________
-initial volume
____________________________________________
volume of base used
____________________________________________
Calculations: Show
all work and include all units.
1. Determine the experimental molarity of vinegar (acetic acid) for each of your trials, and
then determine the average.
Trial 1
Trial 2
Trial 3
2. The label for household vinegar states "5% acidity" which translates to a concentration of
0.83 M. Determine your % error using your average molarity calculated above.
Questions:
1. Write a balanced equation for the neutralization reaction between vinegar and sodium
hydroxide.
2. Explain how the use of phenolphthalein helped to determine the endpoint of the titration.
3. Explain how the concentration of H+ and OH- ions change over the course of the titration,
and how this affected the pH of the solution in the Erlenmeyer flask.
[H+]:
[OH-]:
pH: