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Naked Eggs: Acid-Base Reaction

In this activity, students describe the effects of an acid on an eggshell. The reaction of the eggshell in vinegar is an acid-base reaction. When you submerge an egg in vinegar, the shell dissolves, leaving the inner semi-permeable membrane intact.

Vinegar (acid) breaks apart the solid calcium carbonate crystals (base) in the eggshell into their calcium and carbonate parts. The calcium ions stay dissolved in the vinegar (calcium ions are atoms that are missing electrons), while the carbonate goes on to make carbon dioxide — the bubbles that you see.

The acidic vinegar leaves the membrane that lines the inside of the shell intact. Some of the vinegar permeates the membrane due to osmosis, which is why the egg swells. If you shake the egg, you can see the yolk sloshing around in the white. If the membrane tears, the contents will spill out just the same as with any raw egg, only now they have been "pickled" in the vinegar.

Teacher Tip: Younger students may think that the outer shell has "transformed" into the membrane. Remind them that the outer shell and the inner membrane are two completely different layers. You can crack a raw egg to point out the layers.

Objectives

  • Describe the effects of an acid-base reaction.

  • Identify common acids found in the home.

Materials

  • Per Group of 3–4 students:
    1 raw egg (plus a few extras)
    vinegar (enough to cover an egg in a jar
    a jar or bowl slightly wider & deeper than the egg
    a large spoon
    a flexible measuring tape (like one used for sewing)

Key Questions

  • When you first cover your egg with vinegar, what are the bubbles on the shell’s surface?
  • What evidence is there of chemical change?
  • What reaction is involved to make the shell dissolve?
  • What is keeping the egg contents from spilling out?
  • Is there a difference between the size of the egg at the beginning and at the end of the experiment? What has caused this change?

What To Do

Preparation

Designate a “vinegar pouring station” at your desk so that you can monitor the amount of vinegar students are using (to avoid wasting).

Teacher tips: Repeat the same activity as your students to produce a couple of extra “naked eggs” to use as a control in the related activity Naked Eggs: Osmosis. Also keep the students’ naked eggs for this activity.

Activity

  1. Measure the circumference of the middle portion of the egg.
  2. Place the egg in a jar.
  3. Cover the egg with vinegar and store in a safe place. You should see bubbles forming at the surface of the shell.
  4. The next day, use the big spoon to scoop the egg out of the vinegar.
  5. Discard the old vinegar.
  6. Cover the egg with fresh vinegar and store in a safe place.
  7. Every morning, check on the state of the egg without taking it out of the jar, for about 2–7 days. You only need to replace the vinegar after the first day.
  8. After a week, the egg should be translucent but still pretty much egg-shaped.
  9. Measure the circumference of the middle portion of the egg.
  10. Do not break the egg unless your teacher says you can — you may use it in another experiment!

Extensions

  • Compare the effects of vinegar, plain water, cola, and orange juice on the eggshell. What do the three liquids have in common? How do they differ?
  • Repeat the same experiment with a hard-boiled egg. The eggshell will dissolve in the same way, leaving behind a rubbery egg that should actually bounce as long as it is only dropped from less than 50 cm.

Other Resources

Science World Resources | L’œuf nu : Réaction acido-basique | French version of this resource

Science World |YouTube | Using Purple Cabbage to Do Some Chemistry