Osmosis (idea)

"Osmosis is the diffusion of a solvent across a selectively permeable membrane from an area of lesser solute concentration to an area of greater solute concentration towards equilibrium."

SAY WHAT?

Okay. You can see osmosis for yourself, and it looks pretty cool. All it requires are:

• an egg (raw works best ;-)
• something to put the egg in (such as a jar, mug, or a wide glass, something that's clear really helps)
• vinegar
• karo syrup
• water (distilled water is best, but as long as the water doesn't have a lot of stuff in it (if it's still clear), it's ok).

Here's what to do:

1. Important: You are working with a RAW EGG here. Raw eggs can cause various diseases, so make sure to wash your hands often during this experiment. It's a good idea for kids to get parental permission and supervision for this experiment.
2. Put the egg in the container.
3. Fill the container with enough vinegar to submerge the egg.
4. Wait overnight. The shell will dissolve.
5. Dump the vinegar out of the container, but make sure you don't dump the egg out too. Be EXTREMELY CAREFUL with the egg from now on, because the shell will not be able to protect it.
6. Observe the size of the egg.
7. Add enough karo syrup to submerge the egg.
8. Wait overnight again.
9. Observe the size of the egg. It should now be significantly smaller than before.
10. Dump out the karo syrup from the container.
11. Fill the container again with enough water to submerge the egg. You may want to rinse out the container and CAREFULLY rinse off the egg with water first, to wash away the karo syrup.
12. Wait overnight again. (Sorry about these waits, it just takes time)
13. Observe the size of the egg. It should now be even bigger than when you started off. If you have clean enough water, you can sometimes even get the egg to rupture!.
14. Dispose of the water and egg.

Here's how it worked:

You dissolved the shell, which protects the egg from (among other things) just the torture you were about to give to it!

You put it in karo syrup. The karo syrup is very thick and has a lot of stuff (solutes) in it, dissolved in water, (a solvent). The egg has some solutes in it, but significantly less than the karo syrup. The water in the egg moved outside the egg's plasma membrane, which all cells have. That's right: an egg is really an oversized cell. The water moved outside the egg to balance out the karo syrup.

You put it back in (somewhat) pure water. The water rushed into the cell to balance out the stuff in the cell, making it larger than before... even before the karo syrup. If enough water moves into the egg, the membrane, which is stretchy, like a balloon, will POP.

Look at these diagrams to see what I mean:

Cell in normal environment:

\                     /
 |~~~~~~~~~~~~~~~~~~~|
 | .:      :     .:  |
 |    ___________    |
 |   /  egg      \ . |
 |  | .      .    |  |
 |: |  . . :  .   |: |
 |   \___________/   |
 | .   :     .   .   |
  \_________________/

Cell in karo syrup

\                     /
 |~~~~~~~~~~~~~~~~~~~|
 | .:  ::::: ... .:  |
 |::: ___________   :|
 |   /  egg      \ . |
 |::| .      .    |  |
 |: |  . . :  .   |: |
 |:: \___________/   |
 | .  :::::::. : . ::|
  \_________________/

Cell then gets smaller due to
water going out:
Note how the egg gets more
densely packed with stuff
(solute), and the extra water
spreads the solute in the
karo syrup out

\                     /
 |~~~~~~~~~~~~~~~~~~~|
 | .:  :  :  ... .:  |
 | . ::    .:  :.    |
 |:   ___________   :|
 |   /  egg      \ . |
 |: | . :::  . .. |  |
 |:  \___________/   |
 | .  :: : : . : .  :|
  \_________________/

Cell placed in water:

\                     /
 |~~~~~~~~~~~~~~~~~~~|
 | .                 |
 |         .    .    |
 |    ___________    |
 |   /  egg      \ . |
 |  | . :::  . .. |  |
 |   \___________/   |
 | .             .   |
  \_________________/

Cell adjusts to water:
cell grows, and solutes
inside the cell space out.
The container's solutes
are pushed together by
the growing egg.

\                     /
 |~~~~~~~~~~~~~~~~~~~|
 |  . ___________    |
 |   /  egg    . \ . |
 |  |      . .    |  |
 | .|  ..         |  |
 |  | .   .  .  . |  |
 |   \___________/   |
 | .          .  .   |
  \_________________/

Now back to the original definition, stuff in parentheses are added to explain:

"Osmosis is the diffusion (free movement of something on a small scale) of a solvent (water) across a selectively permeable membrane (the egg's thin membrane) from an area of lesser solute concentration (less stuff dissolved in the liquid) to an area of greater solute concentration (more stuff dissolved in the liquid) towards equilibrium (so that the amount of stuff dissolved inside and outside the egg are about the same)."

Now doesn't osmosis sound a lot easier (and more fun?)