Eggs are good to eat. But eggs can also teach us science. Here are two experiments that you can do with eggs. Remember—even though eggs are food, you should not eat the eggs that you use for these experiments! Eggshells are made of a chemical—calcium carbonate. You can perform a chemical reaction and make the calcium carbonate dissolve. This may sound messy, but eggs actually have a membrane between the shell and the white/yolk that will remain after the shell dissolves. (You can see this membrane when you peel a hard boiled egg.)
The membrane surrounding the egg has a special property. It will allow small molecules (like water) to pass through it, but it keeps large molecules like proteins and fats (the white and the yolk) inside. This process is called osmosis. You can observe this process using the shell-less eggs, water and corn syrup.
Disappearing Egg Shells
• Container large enough to hold eggs
1) Put some eggs in the jar/container. Add enough to completely cover the eggs. What do you see? Bubbles will start to form on the eggs. Cover the container and place it in the refrigerator.
2) Check your eggs after 12-24 hours. What has happened? Carefully remove the eggs from the container and gently rinse them under running water. If some eggshell still remains, put the eggs back into the container and add fresh vinegar. Check the eggs again after another 12-24 hours.
3) When the shell is all gone, make some observations. Carefully hold the egg and notice how it feels. Hold it up to a light—what do you see? With an adult helper, working over the sink, see what happens if you gently squeeze the egg.
Disappearing Egg Shells, Part Two
• Shell-less eggs (3 or more)
• 3 containers
• Corn syrupFood coloring (optional)
1) Label the containers ‘water’, ‘corn syrup’ and ‘control’. Place an egg in each container.
2) Cover the egg labeled ‘water’ with water. Add food coloring, if you’d like. Cover the egg labeled ‘corn syrup’ with corn syrup. If you want use food coloring, add it to the corn syrup before you pour the corn syrup over the egg. Leave the egg in the control container alone.
3) Put the eggs in the refrigerator for at least 6 hours.
4) Carefully remove the eggs from their containers and observe them. What has happened to each egg? Use the uncovered egg (the control) to remind you what each egg looked like before you put it in water or corn syrup. Try putting the egg from the corn syrup into water for a few hours. What happens?
Why does this work?
Eggshells are made of a chemical called calcium carbonate. Calcium carbonate is a base. Vinegar is another name for a chemical called acetic acid which is (of course!) an acid. Acids and bases react with each other. In this case, the reaction makes new chemicals that are soluble in water so the eggshell dissolves. The reaction also creates carbon dioxide gas. If you looked carefully when you put the eggs into the vinegar you probably noticed small bubbles forming. These are carbon dioxide bubbles.
Once the eggshell dissolves, the white and yolk are held in a membrane. Scientists call this membrane semi-permeable because only some things can pass through it. It will allow small molecules (like water) to pass through it, but it keeps large molecules like proteins and fats (the white and the yolk) inside. This process is called osmosis.
In osmosis, the water molecules move from the area with more water molecules to the area with fewer water molecules. The inside of the egg is mostly, but not all water (about 90% water). When you put the egg into pure water, some of the water molecules from the solution move into the egg and the egg swells up. You can tell this happens easily if you use food coloring because the egg will change color. You can also observe that the egg is slightly bigger than the untreated egg.
Corn syrup is only about 25% water. When you put an egg in corn syrup, water will move out of the egg and it will appear shriveled. If you use food coloring in the corn syrup, you may wonder why the egg turns color, if the water is flowing out of the egg. This happens because, while most of the water molecules flow out of the egg, after some time passes, water molecules pass into the egg at the same rate as they are flowing out. This is called a dynamic equilbrium.
If you want to try something else, take the egg that was in the corn syrup and put it into water. What do you think will happen? This picture may give you a clue!
Marshmallows are a soft, chewy, sugary treat. Marshmallows are mostly made from sweeteners (a combination of sugar and corn syrup), which is why they are so sweet. Marshmallows also contain gelatin, which gives them their chewy consistency. What you won’t find on the ingredient list is air—that’s right—air is important for good marshmallows. When marshmallows are made, air bubbles are created during the mixing process, and these air bubbles give marshmallows their puffiness. You can use these air bubbles, and a little science to make marshmallows change size.
Expand Marshmallows by Making a Vacuum
• Glass or thick plastic bottle
• Drinking straw
1) Put some marshmallows in the bottle.
2) Use the clay to seal the top of the bottle. Poke a hole in the clay and put the drinking straw through it. Seal the hole by pressing the clay up against the straw
3) Suck on the straw to remove the air from the bottle. Watch the marshmallows carefully! They will begin to expand as the air is removed. If you have trouble seeing the marshmallows expand, watch what happens when you stop sucking on the straw. The air rushes back into the bottle and the marshmallows will contract immediately. It’s easier to see this because it happens suddenly
Expand Marshmallows by Heating
Be careful—the marshmallow gets very hot!
1) Put a marshmallow on a paper plate and place it in the microwave oven.
2) Set the timer on the microwave oven for 30 seconds (start with this time and make it longer, if necessary)
3) Watch what happens! (This is a dramatic demonstration) Take the marshmallow out of the oven and watch what happens as it cools off. Be very careful, the marshmallow will be extremely hot.
Fun With Ice
Here’s a magic trick you can do to amaze your friends! You can lift an ice cube without tying any knots! Unlike most magic tricks, which use illusions, this one uses science.
Magic Trick Materials
Salt (in a shaker works best)
1) Put the ice cube on a plate. Put a little bit of water on top of it.
2) Cut a piece of string (about 6 inches long). Put one end of the string in the water on the ice cube. Show everyone that the string is not attached to the ice cube.
3) Sprinkle a little salt on top of the ice cube. If you want to be mysterious, you can tell everyone that it is magic powder. If you want to be scientific, you can explain that the salt will melt a little bit of the ice so the string sinks into the cube. Then the coldness of the cube will refreeze the water around the string.
4) Wait a minute or so (it’s a good idea to practice this beforehand, so you know how long it will take). You will probably be able to see the string sink into the ice a little bit.
5) Once you feel confident the string is in the cube, pick it up and amaze your friends!
Why does this work? (And another experiment to try)
Almost everyone knows that water freezes (or melts) at 32oF (0oC). That’s a physical constant, which means that under normal conditions, water always freezes or melts at this temperature. But, we can do something to change the melting point of water. In the winter ice forms on roads and sidewalks, making travel slippery and dangerous. When the temperature is below 32oF (0oC), ice will not melt by itself. To make it melt, people put salt on the ice. Adding salt to the ice lowers the freezing point of the ice (now an ice-salt mixture).
You can see this for yourself, with this easy experiment.