Calcium - an experiment with chalk and lemons answers questions
Upgrade /Log in
Options /Log out
Early Europe
Central Asia
Islamic Empire
Native Americans
S./Central America
American History

Chalk and Lemons

Need chalk? Buy chalk

Take a piece of regular white chalk, like for writing on a blackboard. Make sure the chalk is calcium carbonate like the kind in the picture and not made of plaster of paris. Drop the chalk in a cup of vinegar or lemon juice. Vinegar is made of water and acetic acid, a kind of hydrocarbon. It should fizz up as the oxygen in the acetic acid combines with the calcium carbonate. The bubbles are carbon dioxide that is formed when the oxygen from the acetic acid joins with the carbon from the calcium carbonate.

When it is done fizzing, you should see a layer of little particles of calcium acetate at the bottom of the cup. This is the calcium left over from the calcium carbonate, together with the hydrogen left over from the acetic acid.

Now try the same experiment with an egg. Eggshells are also made of calcium carbonate, so they should do the same thing. If you leave an egg in vinegar for two hours and then take it out, it will feel as if it were made of rubber, and you'll be able to see through it. Be careful so it doesn't break - the shell has dissolved. You may need to change the vinegar once or twice to get it to dissolve all of the shell.

To see that bones are also made of calcium carbonate, try dropping a scrubbed chicken bone in vinegar. How about somebody's baby tooth? Or a piece of marble?

By adding baking soda back to the calcium, you can make it back into calcium carbonate again. Baking soda is made of sodium bicarbonate - molecules of sodium combined with carbon. If you add baking soda and water to the dissolved calcium, the carbon from the baking soda will combine with the calcium to make calcium carbonate again. You should see white particles appear in the liquid.

More about calcium atoms
More chemistry projects

Bibliography and further reading:

Chemistry home

Professor Carr

Karen Eva Carr, PhD.
Assoc. Professor Emerita, History
Portland State University

Professor Carr holds a B.A. with high honors from Cornell University in classics and archaeology, and her M.A. and PhD. from the University of Michigan in Classical Art and Archaeology. She has excavated in Scotland, Cyprus, Greece, Israel, and Tunisia, and she has been teaching history to university students for a very long time.

Professor Carr's PSU page

Help support! (formerly "History for Kids") is entirely supported by your generous donations and by our sponsors. Most donors give about $10. Can you give $10 today to keep this site running? Or give $50 to sponsor a page?

'Tis the season: read all about the history of Thanksgiving, Hanukkah, and Christmas. Who invented Christmas trees? Who were the Maccabees? When was Jesus really born? How did people celebrate Hanukkah in the Middle Ages? Plus, some great gift ideas.