April 6, 2001
Introduce children to science concepts while coloring Easter eggs this spring, advises Diane Bunce, associate professor of chemistry at The Catholic University of America. The project presents several opportunities to demonstrate science concepts to curious kids.
Start with the spin test – a neat way to investigate whether an egg is hard-cooked or not. Spin two eggs on their sides. “The one that is cooked will spin smoothly because the contents of the egg are now solid and move in the same direction as the shell,” Bunce says. “When you spin the raw egg, the liquid contents of the egg don’t move with the shell so the spin you see is less dramatic than that of the cooked egg.”
Sacrifice the raw egg to prove your conclusion, Bunce says. “It’s worth it to teach your child we have the ability to investigate scientific questions and get an answer.”
Dyeing the eggs presents opportunities to teach kids about the attraction of positive for negative charges. Skip store-bought kits and use food coloring instead. Show children why simply dipping the egg in water and food coloring won’t do the trick. Vinegar is needed for the project.
The egg shell is made of calcium carbonate, but the shell also has an additional protein coating. That coating has no charge initially, and that’s why the dye does not stick to it, Bunce explains.
“You put the vinegar into the dye bath because the vinegar, being an acid, enables the protein to acquire a positive charge through a chemical reaction between the vinegar and the protein cuticle,” she says. “The dye molecules have a negative charge when they are mixed with water – thus the dye molecule is attracted to the now-positive end of the cuticle.”
Take your demonstration a step further: remove the protein cuticle by gently sanding a small part of the eggshell. You may have to rub with sandpaper for about five minutes until the section feels smoother than the rest of the shell. “With the cuticle gone, the vinegar will have nothing to react with and there will be no positive charge on the egg shell. Without a positive charge, there will be nothing to attract the negative dye molecule,” she says.
Orange and lemon juices can also be used in the dye bath because they contain citric acid, Bunce says.
For more information on the chemistry of Easter, contact Diane Bunce at 202-319-5390; or e-mail: firstname.lastname@example.org.
Any questions or comments? email@example.com
Revised: April 9, 2001
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