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Titration for Acetic Acid in Vinegar Lab Experiment Summary Titration for Acetic Acid in Vinegar lab Exercise 1 Objectives 1.
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Titration for Acetic Acid in Vinegar Lab
Students will have the opportunity to use titration techniques to determine
the concentration of an acetic acid solution. They will define molarity,
normality, and weight percent.
Peter Jeschofnig, Ph.D. Version 09.2.06
Review the safety materials and wear goggles when working with chemicals. Read the
entire exercise before you begin. Take time to organize the materials you will need
and set aside a safe work space in which to complete the exercise.
Hands On Labs, Inc. LabPaq CK-101 166
To develop familiarity with the concepts and techniques of titration.
To determine the concentration of an acetic acid solution.
Hands On Labs, Inc. LabPaq CK-101 167
Materials From: Label or Box/Bag: Qty Item Description
Student Provided 1 Distilled water
From LabPaq 1 Beaker, 100 mL, glass
Experiment Bag Titration for Acetic
1 Phenolphthalein Solution, 1 - 0.5 mL in
1 Sodium Hydroxide, 0.5 M - 30 mL in
1 Vinegar, 20 mL in a Dropper Bottle
Note: The packaging and/or materials in this LabPaq may differ slightly from that which is
listed above. For an exact listing of materials, refer to the Contents List form included in the
Hands On Labs, Inc. LabPaq CK-101 168
Household vinegar is diluted acetic acid. Its chemical formula is HC2H3O2 and its molecular
weight is 60 grams per mole. A minimum content of 4 acetic acid is required for a product
to legally be labeled vinegar, but commercial household vinegar may actually contain
anywhere from 4 to 8 of acetic acid. The actual quantity of acetic acid in a vinegar
sample may be found by titrating the sample against a standard basic solution.
Titration is the process for determining the exact volume of a solution that reacts, according
to a balanced chemical equation, with a given volume of a second solution of known
concentration. The endpoint of a titration of acids and bases is usually indicated by an acidbase
indicator that has an abrupt and distinctive color change at the point of neutralization.
A popular indicator is phenolphthalein which is colorless in acidic solutions and pink to red
In the past the term molarity M was used when talking about concentration. When dealing
with titrations, the term for the concept of normality N is preferred. The relationship
between normality and molarity is best expressed by the equation
For monoprotic acids M N. Since this experiment deals with a monoprotic acid, this M N
relationship applies, but this would not be true when dealing with diprotic or triprotic acids.
Refer to a chemistry textbook for a more detailed discussion on normality, equivalents,
monoprotic, diprotic, and triprotic acids.
The product of the concentration of the acid expressed as normality and its volume in mL or
drops is equal to the product of the concentration of the base expressed as normality and its
To calculate the normality of the acid, simply rearrange the previous equation and solve:
Once the normality of the acid is determined in moles per liter, the mass of the acid in
grams/moles can be determined by multiplying the normality by the gram-molecular-weight
Assuming the density of vinegar to be 1000g/L, the weight percent of acetic acid in vinegar
The example below reflects a balanced equation of an acid-base neutralization reaction:
Hands On Labs, Inc. LabPaq CK-101 169
It is important to read all instructions and assemble all equipment and supplies before
beginning work on this experiment.
1. Prepare a data table similar to the following to record observations:
Data Table 1: Quantity of NaOH needed to Neutralize 5 mL of Acetic Acid
Brand of Vinegar Used _________________ Label Notes______________________
2. Place a thick text book on top of the
LabPaq box to use as a titrator holder.
3. Use the test tube holder to clamp the
titrator which is simply a 10-mL syringe
4. Place a 100 mL beaker next to the
box/book stack where it will sit under the
5. Place a small piece of white paper under
the beaker to help in the observation of
6. Slip the clamp handle into the textbook at
a level where the stop cock tip is
approximately 1 – 2 cm above the top of
the beaker as shown in the photo.
7. Fill the syringe directly from the NaOH dropper bottle with 9 -10 ml of 0.5 M NaOH
8. Allow a few drops of the NaOH solution to drip into the beaker. This fills the tip of the
titrator and removes any air bubbles from the tip.
Hands On Labs, Inc. LabPaq CK-101 170
9. Pour the few drops of NaOH solution from the beaker down a sink or toilet drain, and
then flush with lots of water. Wash the beaker well with soap and water to remove all
the NaOH solution. Well rinse the beaker, first with tap water and then with distilled
water. Dry the beaker thoroughly before further use.
Performing the Titration of the Vinegar Sample of Unknown Concentration:
1. Read and record in the data table the initial volume of NaOH solution remaining in
the titrator. Read from the bottom of the meniscus and try to interpolate between
calibration lines for as exact a reading as possible.
2. Use a graduated cylinder to measure exactly 5 ml of the vinegar sample and pour it
3. Add 2 drops of phenolphthalein solution to the vinegar sample in the beaker.
4. Place the beaker with the vinegar sample and phenolphthalein drops under the
titrator. Open the stop cock to add only one drop of NaOH at a time to the water
5. Gently swirl the sample in the beaker after each drop and observe the color for five
seconds. Continue adding only one drop of NaOH solution at a time until the
colorless vinegar changes to pink or burgundy and remains that color for at least 30
seconds. Note: Just prior to reaching the endpoint the solution may turn pink when a
drop is added but the color quickly disappears upon swirling or stirring.
6. In the data table record how much NaOH was used by subtracting the final level of the
NaOH solution in the titrator from the initial level of NaOH solution in the titrator.
7. Save the titrator with its remaining NaOH solution for further use. Depending on how
much NaOH you used for the first titration, you may have to add additional NaOH from
the NaOH dropper bottle to the titrator before the next trial.
8. Wash the harmless content of the beaker down the drain. Well rinse the beaker with
distilled water and dry it thoroughly with a paper towel before reusing.
9. Repeat the above titration process two more times. Average the results.
10. Thoroughly clean all your equipment and wash any left over acid or base down the
sink with lots of water. Remember, acids and bases will neutralize each other when
Hands On Labs, Inc. LabPaq CK-101 171
1. Calculate the average number of mL of NaOH used for the 3 trials and record.
2. Calculate the Normality of the vinegar using the previously given equation which is
3. Calculate the mass of the acetic acid in grams using the previously given equation.
4. Calculate the percentage of acetic acid using the previously given equation.
A. What is the average acetic acid in your vinegar sample. How does this compare
with the value stated on the vinegar bottle label.
B. Why is it better to use white vinegar rather than dark vinegar for this titration.
C. Write a balanced equation for the neutralization of acetic acid with NaOH.
D. How would your results have differed if the tip of the burette was not filled with
sodium hydroxide before the initial volume reading was recorded.
E. How would your results have differed if you had over-titrated, i.e. added NaOH beyond
F. What happens if you don t wear goggles and get some NaOH in your eyes.
G. A 5.0 mL sample of vinegar was titrated with 7.2 mL of 0.55 M NaOH aq. If the
density of the vinegar solution is 1.00 g/mL, what is the mass percent of acetic acid present.
