Osmosis vs. Diffusion

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The final lesson plan to go with Travis’s Backyard BBQ Raddish Kids kit was quite scientific and a little over a five-year-old’s head. But thanks to two yummy experiments, even my kindergartner could keep up with the concepts involved.

First, I came to the table with a cup of clear hot water and a tea bag. I put the tea in the cup and asked Travis what he observed happening. “It’s turning golden,” he noticed.

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I agreed, and more specifically told him he was seeing diffusion: molecules moving from an area of high concentration (close together) to low concentration (further apart). This actually wasn’t too foreign an idea for him, since he loves a book about Albert Einstein pondering molecules.

Explain to your child that osmosis is a specific case of diffusion, having to do with the movement of water molecules. Two suggested clips on diffusion and osmosis helped Travis understand a bit better, though to be honest, this part was over his head. To make it more accessible, you can give examples of each. Diffusion might mean:

the aroma you smell from a cake baking

food coloring dispersing in water

Osmosis might be:

wrinkled fingers in a bathtub

rehydrated dried fruit

Now it was time to experiment! For diffusion, I asked him what he thought would happen to a scent if we trapped it inside a balloon. Would we be able to smell it? His hypothesis was yes! We carefully added a few drops of vanilla extract to a balloon.

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Inflate the balloon and tie the end into a knot. Place it in a closed box and let rest for 10 minutes or so.

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When we lifted it out, the box smelled a bit like vanilla; in other words, the scent had diffused. The result was subtle, which I think underwhelmed Travis.

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You may want to leave your balloon inside longer, or put more vanilla in it, to wow your kids with the results.

Next up: osmosis! For this one, we tested out the affect on gummy bears of being in plain water, salt water, and no water.

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We filled out the provided chart with his guess for the results. After some prompting about those plump rehydrated raisins, he was able to surmise what might happen.

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Big kids can really get scientific with this, filling in measurements before and after for color, length, width, thickness, and mass.

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For the set up, you’ll need three clear jars. The first simply received a gummy bear. The second had the bear plus 1/2 cup plain water. The third had the gummy in a saturated salt solution; add 1 teaspoon salt at a time to 1/2 cup water until no more will dissolve.

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We left them overnight, then checked in on the bears the next morning! Again, the results were a bit underwhelming, which may have been the vegan gummy bears we were using. But our plain water one looked a bit more plump, and our salt one looked a bit scrunched.

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Well, if all else fails, you can watch this osmosis rap video!

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