Determining the Calcium Content of Eggshells
Purpose: To determine the calcium carbonate content of eggshells
Background: Calcium carbonate is a component of seashells and eggshells that gives
them their strength and hardness. When calcium carbonate reacts with hydrochloric acid,
the products are carbon dioxide, water, and calcium chloride.
CaCO3 (s) + HCl (ag)  CaCl2 (aq) + CO2 (g) + H2O (l)
You will be adding hydrochloric acid to an eggshell to dissolve all of the calcium
carbonate in the shell. The portion of the eggshell that is not calcium carbonate does not
react with the acid and remains a solid. You will be separating the solid parts of the
eggshell from the calcium carbonate by filtration. This will allow you to determine the
percent of the eggshell that was calcium carbonate.
Safety: You will be working with concentrated hydrochloric acid. Goggles must be worn
at all times during this lab. If you get any of the acid on your skin wash your hands with
soap and a lot of water.
Procedure:
1. Obtain a piece of eggshell and crush it. Transfer the eggshell to a 250 ml beaker and
find its mass.
3. Add 45 ml of 1.0 M HCl to the eggshell and stir with a glass stirring rod until there are
no more bubbles forming.
4. Find and record the mass of a dry piece of filter paper. Write your name and period
number on the filter paper with a pencil. Fold the filter paper and put it in the funnel. Set
the funnel over an Erlenmeyer flask.
5. Pour the dissolved eggshell and acid through the filter. Wash the filtrate with a little
deionized water.
6. Put your filter paper in an 80 ml beaker with your name on it and bring it to the oven to
dry until tomorrow. When the filtrate is dry find its mass.
Calculations:
- Calculate the mass of the filtrate by subtracting the mass of the filter paper from the
mass of the filtrate and the filter paper.
- Calculate the mass of the calcium carbonate by subtracting the mass of the filtrate from
the mass of the eggshell.
- Calculate the percent of calcium carbonate in the eggshell by dividing the mass of
calcium carbonate by the mass of the eggshell and then multiplying by 100.
- Calculate the number of moles of calcium carbonate in your sample.
- Calculate the number of formula units of calcium carbonate in your sample.