A 2-for-1 experiment; Day 1 is an Acid-Base Reaction, Day 2-3 is the Osmosis Portion. Though it covers 3 days, the entire time spent on the project is 15-45 minutes.
Dissolving the shell
1) Place 4 eggs in a container, cover with white vinegar.
2) Add some “fresh” vinegar (or just replace with fresh vinegar)after about 8-12 hours.
Vinegar is an ACID; eggshells are made of calcium carbonate (BASE).
Reacting Acids and Bases
3) These are the eggs after about 2 hours. Look at all those CO2 bubbles!
4) You should have “naked eggs” (just the membranes) within 24-48 hours after starting
(For more on the chemistry: http://goo.gl/zOhCk)
1) Remove and gently rinse your naked egg under running water. Compare it to a fresh egg. It looks (and feels) MUCH different now that the shell is gone!
2) Hold the egg up to light and look at the yolk. Boo said the egg feels like a water balloon.
3) Once the shell is off, the egg will get MUCH larger! This is due to osmosis – there is more water in the vinegar than in the egg. The water will diffuse from the area of high concentration (vinegar), into the area of low concentration (egg), across the membrane. Diffusion occurs until equilibrium occurs, (after that, exchange takes place at a steady rate).
(For an easy-to-follow definition and animation of diffusion and osmosis: http://goo.gl/IRxXi)
Osmosis with Eggs
1. Label cups clearly for water, vinegar, and corn syrup.
2. Put one naked egg in each cup.
3. Cover each egg with the appropriate liquid.
Thing 2 helps Thing 1 demonstrate diffusion across a selectively permeable barrier. With Matchbox cars and a baby gate.*
After the demonstration, Thing 1 came up with his hypothoses:
1) The egg in corn syrup will shrink, because Corn syrup doesn’t have water in it. The water will diffuse from the egg into the syrup.
2) The egg in the vinegar will stay the same size, because it’s already been soaking in the vinegar long enough that it is in equilibrium (same concentration of water in AND out of the egg)
3) The egg in the water will get even bigger, since there is a higher concentration of water in the water (!) than in the egg.
*Large stuffed animals were also involved, but since this is a SELECTIVELY PERMEABLE barrier, they were unable to cross and stayed in a corner by themselves.
Edited: For that matter, the children are also unable to cross this particular selectively permeable barrier. Who says parenting isn’t a science.
Having soaked overnight, the eggs are dramatically different in size and feel.
1) The naked egg soaked in corn syrup is the smallest
2) The naked eggs soaked in vinegar and water aren’t significantly different from each other, visibly. However, you can tell a distinct difference by touch (the naked egg soaked in water is much more taut).
This observation seems to confirm Andrew’s hypotheses from yesterday, but the fun isn’t over yet!
3. How are the eggs different? How are they similar? What do you think caused the differences?
The egg soaked in corn syrup looks much different than the fresh egg, too.
Breaking the Water Egg
Scientists always make the best of any “woops”. This is true.
This surprised us! The absorbed water hadn’t been incorporated into the egg white or yolk. You can see the white and yolk intact in the middle of the huge splash of water. All of that water (plus the water on the boys’ shirts, plus the water on the floor) was inside the naked egg.
Breaking the Vinegar Egg
Squeezing till the egg broke was a bit grosser than he expected it to be (sometimes science is messy).
Breaking the Corn Syrup Egg
Because I’m the mean mommy, I didn’t let him squeeze this egg ’till it popped.
He *really* wanted to.
1) Look at the membrane (the consensus is that it feels like a flower petal).
2) Compare the volume of the broken Corn Syrup Egg to the volume of the broken Vinegar Egg. It’s pretty impressive; I wish we would have thought to measure the volume.
Who gets a Brownie Point? Did you notice we started with 4 Naked Eggs and finished with 3? That was my fault, not the kids!