Osmosis, An Accidental Experiment

Last week we finished our unit study of the world's oceans. We had a surprise or accidental experiment last night when the girls notice that one of those starfish toys that you put in water and it swells to way larger than it was to begin with had shrunk. It had been sitting in a bowl of water for the past week. They couldn't figure it out because a few days ago it had increased to three times the original size. They kept questioning why it had suddenly shrunk. Then McKenna looked at the water. That's when we discovered that little Miss McLarin had added salt to the water. A lot of salt!

We did a little investigating and learned that this was due to osmosis. When the toy had increased in size water was more abundant in the cells or fibers of the toy. Adding salt caused the water to be drawn into the salt water and out of the toy. The toy had more water and less salt and the water outside the toy had way more salt. Apparently the cells of this toy starfish were trying to equalize the amount of water inside and outside of itself.

The girls starfish toy has shrunk a size or two from the size it was a few days ago, but is still larger than when it was put into the water. How's that for a cool accidental experiment?




The picture of me holding the toy starfish
helps show the actual size of the starfish.
When it was put into the water it was about
3" across. It then swelled to about 9" across.
Now after the salt was added to the water

Can you see that big pile of salt under the starfish?

it has shrunk to about 5-6". Sorry I don't
 have a picture of it when it was at it's
 largest size. Hope you enjoyed sharing
in our fun learning experience!

Why Doesn't The Ocean Freeze Solid?

Ever wonder why the oceans don't freeze solid? Well we have and we decided to investigate to find out. We had to make some cccold water! If you try putting it in the freezer you'll find you end up with ice pretty quickly instead of super cold water. But we found an experiment that showed us how to cool water down to it's freezing point without freezing it solid!

Supplies Needed

Freezer
Spoon
Water
Salt
Ice
two plastic cups (we ended up using two glass canning jars)
marker

Deep Freeze Experiment

1. First fill both plastic cups with the same amount of water.
2. Add four heaping tablespoons of salt to one of the cups. Mark this cup with an S.
3. Place both cups in the freezer and make sure they won't fall over.
4. Check the cups every hour for the first four hours then leave them overnight and check the next morning. What's the difference between the two cups?

What's Going On?

Water normally freezes at around 0 degrees C, but adding salt to the water lowers it's freezing point. The salt makes it more difficult for the water to freeze solid so the water can be be colder that 0 degrees and still not freeze completely. Salty water will eventually freeze, but the water has to be a lot colder than ordinary water.

To prove this check the cup with the plain water. It should freeze in about four hours, but the other cup may not freeze at all. Instead there may be a tiny bit of ice that forms, but only after it gets rid of the salt. To do this the salt sinks to the bottom. The same thing happens in the ocean around Antarctica.