The egg’s membrane is permeable to water. While random molecular motion will cause individual molecules to continue moving back and forth across the membrane, the overall concentration on each side will remain in equilibrium, with equal concentrations on both sides. This movement will continue until the concentration on both sides is the same.
They will move through the membrane from the side where they are at a higher concentration to the side where they are at a lower concentration (click to enlarge the diagram below). Substances that can pass easily through the membrane of the egg will follow the principles of diffusion. This membrane, like those in human cells, is selectively permeable, allowing certain substances to pass through while blocking others. After the eggshell is removed, a thin membrane (actually, two membranes held tightly together) remains. The de-shelled eggs serve as good models of human cells. Eggs buried in salt or other dry media should lose mass. Eggs in dilute salt solutions will gain mass, and even those in very concentrated solutions might gain mass. Eggs soaked in distilled water will gain mass and appear dramatically swollen. Eggs submerged in corn syrup will have lost considerable mass and have the appearance of flabby sacks. In general, the most dramatic changes to the mass, color, and shape of the eggs will occur within the first 24 hours of the experiment. How did each egg change? Did its mass increase or decrease? Do you see anything in common with the treatments that enlarged the eggs? Which treatments made the eggs shrink, and which did not? In a separate bowl, carefully dissect the egg by piercing the membrane. Calculate the percentage change in mass for each egg by dividing the final mass by the starting mass and multiplying by one hundred percent. Remove the plastic wrap from the control egg and measure its mass too. Then, gently remove your sample eggs from their treatments to measure and record the mass of each one (see photo below). Observe any changes in the color, size, or shape of your experimental eggs. Observe any changes that occur in the eggs during the first hour or so of soaking and record your observations. Place the treatment containers somewhere they can sit for at least a day at room temperature. After taking its mass, cover the control egg with plastic wrap, and set it in a container alongside the treatment eggs. Be sure to set aside an untreated "control" egg. Place one egg in a labeled container and cover it with your chosen treatment. (If the egg floats, you may use something to hold it down, such as a glass jar see photo below.) Repeat for each of the remaining treatments. Use a scale to find the mass of each de-shelled egg before treatment. Remember to label your containers as you work. You can make solutions of food coloring by adding a few drops of each color into containers of water. You can make salt-water solutions by dissolving different amounts of table salt in containers of water (e.g. Determine the treatments you’ll be using on your eggs, and prepare the substances you’ll need.Try to keep them off carpeted areas, and soak several extra eggs, just in case. But despite your best efforts, some eggs will break. Note: Be sure to handle the de-shelled eggs gently. Cover and refrigerate the de-shelled eggs until ready to be used. Gently rinse the eggs in water to remove any traces of softened shell. The eggshells will leave residue in the vinegar bath (see photo below).Note: Changing out the vinegar halfway through and replacing it with fresh vinegar will speed up the process. Allow the eggs to sit for 24 to 48 hours at room temperature. Add vinegar to cover the eggs (see photo below), and cover the container. De-shell the eggs by placing them in a large container so that they touch as little as possible.
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