The egg osmosis experiment is a classic school project that shows how water can move through a thin membrane. First, vinegar dissolves the hard eggshell, leaving a soft, rubbery naked egg surrounded by its membrane. When the naked egg is placed in corn syrup or sugar syrup, it shrinks, and when it is placed in water, it swells.
This makes osmosis easy to see because the egg changes size in a way students can measure.
Key Facts
- Osmosis is the movement of water across a selectively permeable membrane from lower solute concentration to higher solute concentration.
- Vinegar removes the eggshell because acetic acid reacts with calcium carbonate in the shell.
- Calcium carbonate + acid produces carbon dioxide gas, which appears as bubbles on the egg.
- In syrup, water leaves the egg because the syrup has a higher solute concentration than the egg interior.
- In water, water enters the egg because the egg interior has a higher solute concentration than the surrounding water.
- Percent change in mass = (final mass - initial mass) / initial mass x 100
Vocabulary
- Osmosis
- Osmosis is the movement of water through a membrane toward the side with more dissolved particles.
- Membrane
- A membrane is a thin barrier that controls what can pass into or out of a cell or egg.
- Solute
- A solute is a substance that is dissolved in a liquid, such as sugar in syrup.
- Solution
- A solution is a mixture in which one substance is dissolved evenly in another substance.
- Selectively permeable
- Selectively permeable means a membrane lets some substances pass through but blocks others.
Common Mistakes to Avoid
- Skipping the vinegar step is wrong because the shell must be dissolved before water can move easily through the egg membrane.
- Poking or squeezing the naked egg is wrong because the membrane can tear and ruin the experiment results.
- Comparing eggs without measuring mass or size is wrong because visual changes can be hard to judge accurately.
- Thinking syrup pushes the egg smaller is wrong because the egg shrinks mainly because water moves out through the membrane.
Practice Questions
- 1 A naked egg has a mass of 62 g before being placed in syrup. After 24 hours, its mass is 44 g. What is the percent change in mass?
- 2 A naked egg has a diameter of 4.0 cm after soaking in syrup. After it is placed in water overnight, its diameter becomes 5.2 cm. How much did the diameter increase, and what is the percent increase?
- 3 Explain why a naked egg shrinks in syrup but swells in water, using the ideas of membrane, solute concentration, and water movement.