Oil and Water DO Mix!

I started down this path because one of my scouts, H, was extremely interested in chemistry.  H was a 3rd grader Bear Scout who was asking me very insightful questions about how chemicals come together.  I had that in mind when I found a recipe for "Bubble Dough".  Just making Bubble Dough wouldn't cut it as a STEM Den meeting, so I combined it with an intro to polar and non-polar molecules, as well as the Color Changing Milk from Steve Spangler.


 Bubble Dough Recipe
amounts are approximate, just keep adjusting until it looks like play dough
1 part body wash or liquid hand soap
4 parts corn starch
Combine until it resembles dough. Store in an airtight container. Use dry hands to remove from container.  Use a pea sized amount to wash hands, about a small grape for a shower. When washing hand, rub until the bubble dough disappears (takes about 1 minute!)


I opened by telling showing oil layered on top of water.  I explained about polar and non-polar molecules.

Water is polar, which means on different parts of the water molecule, there's a little bit of a charge.  An important thing to remember is that polar molecules like other polar molecules.  Oil is non-polar, which means that whole molecule has the same "charge", which is "no charge".  Non-polar molecules like other non-polar molecules.

Then, I divided the group in half, and each kid got 2 pieces of paper.  For one group, both pieces were "0" which was the "non-polar" group.  The other group each got one "+" and one "-" and they were the polar group.  I told them to match up and explained how they looked like the glass of oil floating on the water.

There are two ways to get oil and water (or polar and non-polar) solutions together. The first is "emulsification", which is when you take a third substance called an emulsifier.  The emulsifier allows the non-polar and polar substances to combine.

I let them guess what an emulsifier would look like and then explained it as half polar and half non-polar.  I asked for one of the non-polar kids to be a volunteer and turned the rest of the group into an emulsifier by putting a "-" on their backs.  Have the non-polar kid stand in the middle of the room, and surround him with emulsifiers then with waters.

What you've formed is a micelle, which is when a bit of oil surrounded by an emulsified surrounded by water.  The micelles are so small that it looks like a solution.

Another way to get polar and non-polar solutions together is called homogenization, which is why you don't see a fat layer on top of milk any more. Back in the old days, you could still get milk with the cream floating on top. Now, they homogenize it, which is forcing it through extremely small holes at high pressure.  But, you can pull the fat out of the milk by using an emulsifier.

This is when we did the Color Changing Milk experiment.  Helpful hint: liquid food dye works better than gel or paste dye.

 Now that we know soap is an emulsifier, how do you think soap gets you clean? It surrounds the non-polar dirt and allows water to wash it away. Also, bacteria (germs) usually have a fatty outer layer and washing your hands with soap for enough time is an important way to stay healthy.

We finished by making the Bubble Dough recipe.