KEVI Chemistry
It’s that time of year when we can’t walk into a store without seeing displays of chocolate bunnies, marshmallow
chicks, and vibrant bouquets of owers. Along with all these springtime treats, perhaps the most memorable
and engaging tradition (and my personal favorite) is the dyeing of Easter eggs.
Decorating eggs is a deeply rooted, international tradition. The oldest examples of this activity are the engraved
ostrich eggs found in Africa 60,000 years ago. Eggs across many countries and cultures are celebrated, and
whether these activities are based on religion or the coming of spring, eggs represent rebirth and life.
For those who have participated in egg dyeing, you may have wondered: Why is vinegar added to the dye
solution? This can be explained through simple chemistry. You've probably heard of acids and bases - it turns
out that all solutions have a degree of acidity or basicity. Acids chemically react with bases to create solutions
that are more neutral – that is, closer to pure water.
So, back to the initial question – why is vinegar needed to dye an egg? The answer is that most egg dyes need acid
to bind the dye to the eggshell. Vinegar is an acid, and eggshells are bound together by a basic molecule called
calcium carbonate. The eggshells base molecules assure that neutral and basic solutions will not change the
eggshell. However, vinegar will react with the calcium carbonate shell to dissolve it slightly, allowing the dye
molecules to stick to the eggshell, giving you vibrantly colored eggs. Without adding vinegar to your dye
solution, you will likely get very faint coloring.
( Egg in vinegar. The bubbles on the shell are from gas released when the vinegar reacts with the calcium
carbonate. Leave this overnight and the eggshell will dissolve! )
Have you ever tried changing the amount of vinegar added to your dye solution? Because acid is needed for the
dye molecule to stick to the egg, you might predict that adding more vinegar to the solution will give you more
colorful eggs. This may be true to an extent, but be careful! The acid reacts with calcium carbonate to produce
carbon dioxide gas, which will oat out of the solution, like carbonation in soda. This gas forming on the surface
