Osmosis is the process by which water enters our tissues. All of our cells are surrounded by a membrane that allows water to enter or leave the cell, but selectively allows other things to enter or leave. This works because the membrane has several tiny holes that will let small molecules through, but will stop big molecules from entering or leaving the cell. Water is small enough to get through and enter or leave by a process called diffusion. Diffusion means that the water molecules will pass from an area with a higher water conentration to an area of lower concentration until it is balanced out with both substances having the same concentration (isotonic). May be referred to as reaching an equilibrium. An egg also has a membrane surrounding it so we can use it to represent a cell and see how osmosis works. In the following experiment you will see the action of osmosis.

Try this experiment.

These supplies are needed:

3 eggs
4 cups vinegar
2 cups tap water
2 cups corn syrup
It is important that you read through the experiment in its entirety before beginning. You will need to write a hypothesis before you begin that predicts the results of your experiment. Write your hypothesis based on the following questions: What do you think will happen when an exposed egg (egg without its outer shell) is place in water? What do you think will happen when an exposed egg is placed in corn syrup?

Instructions. 1. Place 2 eggs in jars with 2 cups vinegar each. The acetic acid (CH3COOH) in the vinegar will cause a chemical reaction with the calcium carbonate (CaCO3) eggshell and dissolve the shell, leaving only a rubber-like semi-permeable membrane around the liquid portion of the egg. This may take a few days – be patient. The reaction may be written as follows: 2CH3COOH + CaCO3 --> Ca(CH3COO)2 + CO2 + H2O; or reads like this: 2 molecules of acetic acid combined with calcium carbonate yields calcium acetate and carbon dioxide and water. 2. Remove the shell-less eggs from the vinegar. 3. Place one shell-less egg in a jar with 2 cups tap water. 4. Place one shell-less egg in a jar with 2 cups corn syrup. 5. Observe the eggs after one day and two days.
What two molecules (chemicals) are involved in dissolving the egg shell? 6. Each time, compare the egg in water and the egg in corn syrup to the egg that had nothing done to it. 7. Answer the questions to the best of your ability. Questions What do you observe after twenty-four hours? After 48 hours? What two molecules (chemicals) are involved in dissolving the egg shell in the first portion of experiment? When one of the eggs was first placed in tap-water, was the concentration of water greater ¬inside or outside the egg? Explain. When one of the eggs was first placed in the corn syrup, was the concentration of water greater ¬inside or outside the egg? Explain. Based on what you have learned about semi-permeable membranes and osmosis, write a conclusion that explains the results of this experiment. Conclusion: Begin by stating whether the hypothesis was true or false. Use data and calculations to support your answer. Consider the following questions as you write your conclusion: Why or what happened to result in the outcome you observed? Did you learn anything new? If not, what previously concepts did this lab reinforce? Is there anything you would or could do differently that would improve the experiment? Do you have any other comments/observations you would like to share about this lab?