Saturday, September 10, 2011

Osmosis Eggsperiment

This was the osmosis learning experiment from about a week ago!!
1. Soak three eggs in vinegar...You really only need two, but I did an extra, because I know my kid...He was gonna wanna squeeze and squish the 'goo' out of one of those poor eggs. You soak the eggs for 24 hours and the vinegar basically  eats the shell off. The real scientific explanation to this the child received was about the chemical reaction occurring as the vinegar reacts with the shell causing it to dissolve and allow the formation of the air bubbles in the vinegar as the gas escapes from the shells, allowing them to thin and just the egg lining or egg membrane to remain.
Acetic Acid + Calcium Carbonate = Carbon Dioxide release
We also discussed the calcium of the shell being much like the calcium found in a bone of an animal, which is why they are white. His contrasting statement to this is when scientists found dinosaur bones, they were more a dingy whitish brown color than white. We discussed the white calcium being a semipermeable substance once hardened...which is why x-rays and MRIs can be made of bones. (Side bar discussion occurred here about his knee (re)injury and upcoming MRI to be scheduled yet.) We got out the periodic table and discussed calcium being an element need for survival and plant growth and such.

starting to soak

carbon dioxide releasing

better picture of all the CO2 bubbles collecting at the top of the vinegar

We took the eggs out of the vinegar after about 1.5 days of them soaking. The remainder of the egg residue was easily washed off. I did explain to the child that the egg membrane was fragile and so he had to handle it carefully.






This was also a good lesson that referenced back to the original cell lesson many weeks back it seems like now. The egg is more like a cell and the child could see the yolk inside once the shell was washed away, because the egg membrane is porous and somewhat translucent. We discussed how the albumin or egg white was like cytoplasm. This is where the lesson on osmosis begins. We discussed what it was and how it could occur in cells. My husband gave him a simpler explanation and example later in the week to think of osmosis like a sponge soaking up water; it moves from the container to the sponge. Another thing that is observable about the eggs at this time is that the yolk is slightly centered.

The next step is to take two glasses filled with water. One glass contains plain water and one glass is mixed with an equal amount of dissolved sugar. You place one egg each in each glass of water.

The plain water glass contains the sinking egg. The floating egg is in the sugar water mixture.

top view of sank egg

top view of floating egg

The egg in the sugar solution floats because the sugar solution is dense, moreso than regular plain water. After soaking for slightly more than 1.5 days in the water and sugar mixtures, we removed the eggs. At this point is is observable that one egg is larger than the other. The egg on the right was the water egg. The egg on the left is the sugar egg. Notice how the yolk has sank to the botton of the sugar egg. The egg from the water is so waterlogged, it is difficult to see the the yolk anymore.

The dissolved sugar contains dissolved molecules that are too large to move through the semipermeable membrane of the egg. Water molecules are smaller than sugar molecules. Water molecules are small enough to pass through the egg membrane. Water is contained within the egg itself, before we ever soaked it in any solution. Osmosis seeks to make the concentration level the same on both sides of the gradient by moving through the membrane to stabilize the equality of water on both sides of the membrane. The water of the sugar solution egg will move out of the egg to the sugar solution to stabilize the solutions on both sides. There are more water moecules in the water solution than in the egg itself. Thus, the water molecules move across the cell membrane of the water solution egg to stabilize the water amount on both sides of the egg membrane. The water leaving the sugar solution egg causes the egg to shrink. The water entering the water solution egg causes the egg to swell.

The next step was to prick the water enlarged egg. It was supposed to spout the water out. Of course, my kid squeezed the egg once it started to spout and tried to make it spew...needless to say, the egg exploded...remember there was 3 day old, sitting out on my counter top and in vinegar) egg yolk still in that egg membrane.

pricking the egg - it spouted before I could snap another picture

straight from spouting water to exploding in his hand : /

leftover cell membrane

of course, the sensory side of him has to touch it before it is cleaned up

Next, place the sugar solution, shrunken egg into the older water solution. We had to start over with a new cup of water, because the child had thrown out the older water. When you place the sugar water egg back into regular water, it will slightly return to a more normal size. It reabsorbs water into the egg membrane to equalize the gradients again. Yes, the child had to prick the sugar solution egg once it was norml size again. Yes, he thought it would be equally cool to squish it too!!  Don't forget we had the extra vinegar egg in the fridge all this remaining time. He remembered the extra vinegar egg about 2 days after the experiment ended and promptly poked it with a stick pin to squish it as well.

While we were conducting the above, we also boiled another egg and then soaked it in vinegar to eat the shell off of it. The child washed the shell off of it and it was bouncy, from short heights only. Yes, it was eventually squished outside as well. Needless to say, the child enjoyed this eggsperiment.
egg after boiled water cooled

boiled egg soaking in vinegar

carbon dioxide release with boiled egg

shell is starting to dissolve
 we found this interesting that the part of the egg where the air sac is located at the end of the egg was able to be wrinkled. the shell is still on there at this time, though slightly dissolved...


water egg, sugar egg, and boiled egg all with shells gone...cell membrane of boiled egg is intact with slight wrinkles.

1 comment:

  1. the idea for this experiement came from http://www.science-sparks.com/2011/08/29/shrinking-eggs/

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