Handout: Determining the Percentage of Acetic Acid in Vinegar
Using Eggshells
Adapted from 40 Low-Waste, Low-Cost Chemistry Labs, J.
Weston Walch, 1997.
Time Allotted: 30 minutes
Objective: Eggshells are composed of calcium carbonate. The
products of the reaction between calcium carbonate and acetic acid are
carbon dioxide, water, and calcium acetate:
CaCO3 + 2HC2H3O2
CO2 + H2O + Ca(C2H3O2)2
In this experiment eggshells will be used to determine the percentage
of acetic acid in vinegar.
Materials:
Eggshells (membrane removed)
125 mL Erlenmeyer flask or a 5
oz cup
Stirring rod
25 mL vinegar
Coffee filter paper or filter paper
Balance
Graduated cylinder or a
syringe
Paper towels
Safety: Wear chemical splash goggles, gloves, and an apron. Use
caution in working with acids.
Disposal: Flush the neutralized solution down the drain. Return
unused acetic acid to the supply area.
Task:
1. List several questions you or your group members have
about determining the percentage of acetic acid in vinegar.
2. Perform the following procedures and record your data and
observations in the section provided.
Procedures:
1. Using the graduated cylinder or a syringe, transfer 25 mL of
vinegar to a cup. (1 cc = 1 mL)
2. Break the eggshell into small pieces (Do not grind).
Determine the mass of an empty coffee filter paper or filter
paper and determine the mass of the eggshell plus the filter
paper to +/- 0.01 grams by taking the difference in weight.
Record your results in the data table. Don’t discard the
filter paper used here!
3. Add the eggshell to the vinegar. Use the stirring rod to
ensure all the shell is below the surface of the vinegar.
4. Swirl the cup to speed up the reaction and then allow the
reaction to proceed for several hours (4-6 hours) until the
gas bubbles stop rising.
5. Filter the vinegar/eggshell mixture. To filter, take the coffee
filter paper or filter paper used in step 1 and make a filter
funnel by folding it in quarters. It should look like the
diagram below. At the top of the cone, pull 3 layers of the
filter paper to one side leaving one on the opposite side.
Hold the filter over a cup and pour the eggshell/vinegar
mixture into the filter. Allow gravity to help move the
vinegar away from the eggshells.
6. Allow the eggshells collected in the filter paper to dry
together with the filter during overnight.
7. On the following day determine the mass of the dry eggshell
to +/- 0.01 grams as you did in step 1. Record in the data
table.
Data and Table:
Mass of eggshell.
Volume of vinegar.
Mass of dried eggshell.
Calculations (record results in the calculations table):
1. Determine the mass of eggshell reacted by subtracting
the mass of the dry eggshell from the mass of the
entire eggshell.
2. Assuming the eggshell is 100% calcium carbonate;
determine the number of moles of calcium carbonate
used in the reaction.
3. Using the balanced equation, determine the mole ratio
of calcium carbonate to acetic acid. Determine the
number of moles of acetic acid neutralized using the
mole ratio.
4. Calculate the molar mass of acetic acid. Determine
the number of grams of acetic acid present by
multiplying the molar mass by the number of moles of
acid.
5. Determine the percentage (by mass) of acetic acid in
the vinegar sample using the volume of the sample
and the mass of acetic acid.
6. Were any of the questions you or your group had
answered by this activity? If so, which ones?
Calculations Table:
Mass of eggshell reacted.
Moles of CaCO3 reacted.
Mole ratio (CaCO3 : HC2H3O2).
Moles of Acetic acid.
Grams of Acetic acid in sample.
Experimental percentage.
Accepted percentage.
Percentage error.