Summary

In this demonstration, students will first observe a reaction between vinegar (acetic acid) and an egg shell (calcium carbonate) to produce a naked egg. Using these eggs, student will analyze how certain substances can move through a membrane and also determine if the membrane is affected.

Grade Level

Elementary and Middle School

Objectives

By the end of this demonstration, students should be able to

• Understand the definition of osmosis.
• Make observations.
• Analyze the concentration of a solution based on its interaction with a membrane.

Chemistry Topics

This demonstration supports students’ understanding of:

• Solutions
• Concentration
• Solute
• Solvent
• Passive Transport
• Chemical Reactions
• Chemical Change

Time

Teacher Preparation: 10 minutes

Lesson: 45 minutes

Materials

• 4 raw eggs
• 4 wide glasses (should hold an egg and approximately 2 cups of liquid)
• 8 cups of white vinegar
• Red food coloring
• 4 cups of water
• 2 cups corn syrup
• 2 cups molasses
• Permanent marker
• Tape measure
• 4 toothpicks
• Soup spoon
• Plastic wrap or foil to cover the eggs in the glasses (optional)

Safety

• Students should wear proper safety gear during chemistry demonstrations. Safety goggles and lab apron are required.
• Do not consume lab solutions, even if they’re otherwise edible products.
• Food in the lab should be considered a chemical not for consumption.

Teacher Notes

• Show the video, “Osmosis" from Khan Academy during class or assign it for homework (8 minutes in length).
• Before class begins, set up a table with the materials in the front of the classroom. Make sure that every student will be able to observe the demonstration from where they are sitting.
• Day 1: Explain/review/discuss the following terms and their definitions. Explain to your students that you are about to demonstrate these.
  • diffusion
  • osmosis
  • solute
  • solvent
  • solution
  • passive transport
• Display the following chart on a SmartBoard or dry erase board. Keep this visible while discussing this topic and add to the chart as a part of whole class instruction.

Demonstration Procedures:
Day 1:

1. Place one egg in each of the four glasses.
2. Fill the glasses with 2 cups of white vinegar each (or until egg is completely covered).
3. Explain to the students that the vinegar will react with the shell to slowly remove it. It will take time for the shell to disappear so it must be left in the vinegar for 72hrs.

Day 2:

1. Allow students to observe the eggs and see that the shell is no longer visible and the inner membrane is left holding the egg together.
2. Empty the vinegar and rinse the eggs before placing them back in the glasses. Use caution when handling the eggs as they are very delicate and the yoke could break.
3. Label the glasses #1-4.
4. Ask a few students to use the tape measure to record the length of each egg. Record it in the class data table.
5. Each egg will be covered with approximately 2 cups of a different substance. Egg #1 will be covered with corn syrup, egg #2 with molasses, egg #3 with water, and egg #4 with 2 cups of water and a drop of red food coloring.
6. Optional: Students can make predictions about what will happen, but they will have to wait until the next day to see the results.

Day 3:

1. Remove the eggs from each container and rinse them carefully with water.
2. Ask a few students to use the tape measure to record the length of each egg. Record it in the class data table.
3. Explain that water moves through the membrane easily. Bigger molecules—like the sugar molecules in the corn syrup—don’t pass through the membrane. When you put a naked egg in corn syrup, you are creating a situation where the egg membrane separates two solutions with different concentrations of water. The egg white is about 90% water; corn syrup is about 25% water. In this situation, movements of water molecules cause them to move from the side of the membrane where they are more abundant to the side where they are less abundant. So water migrates from inside the egg to outside the egg, leaving the egg limp and flabby. Record observations in the table.
4. After students have observed and analyzed each of the eggs, use a toothpick and pop each egg and ask questions about the student’s observations.
   • “What does the increase in the width of the egg tell you?”
   • “What does it mean if the width stayed the same?”

• Differentiation: Use additional/different solution, such as salt water, pure water, etc.
• For older or more advanced students, you may consider doing this as a lab activity, and have students carry out the procedures on their own.
• Movies that could tie-in to the lesson: Osmosis Jones (2001)
• Post-demo real world connection: I found that you could relate this to several different things.
  • The egg in vinegar can be used as a way to show your students how acid interacts with calcium to cause tooth decay. Of course, putting an egg in vinegar isn't exactly the same as not brushing your teeth, but the bacteria in your mouth stick to the hard surfaces of your teeth. Some of these bacteria create acids when they are combined with the sugar in foods and beverages. These acids can break down the enamel of your teeth if you don't brush often so we should be careful about how the amount of sweets we eat.
  • Connect this into a biology lesson relating it to cells in the human body and what happens when eating foods with high salt.