Practicing Science Together: A One-room Schoolhouse Model for Authentic Inclusive Secular Science Experiences

Water Lesson 3: Solvent Properties

People sometimes call water the “universal solvent.” This is absurd. It feels like the universal solvent because it’s the one that so many biological systems depend on, but it is only a solvent for molecules that are polar (charged particles that are positive at one end and negative at the other) or for ions (charged particles). That’s why lots of vitamins are fat-soluble. And why it’s important to “temper” or “bloom” spices and herbs in oil. Those big uncharged organic molecules that we sense with our noses and tastebuds? Guess what? They don’t dissolve in the “universal solvent” that is the ever-so-polar water. I learned this in the laboratory of Dr. Julia Kubanek.

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Dr. Kubanek is a Chemist and Biochemist who studies, “How do marine organisms use chemicals to solve critical problems of competition, predation, disease, and reproduction?” Her research involves a lot of finding out what chemical makes certain processes occur. That means that the laboratory researchers are separating mixtures of chemicals (often based on what solvent they dissolve in) and then putting the separate parts back into the test system until they get a single compound that causes the response. So, for example, if a blueberry muffin baking makes my mouth water and I want to know why, maybe I bake each individual ingredient to see what has the same effect. If I don’t know the recipe, I would need to maybe mash up the blueberry muffin and separate out the parts. I might start by what looks different because a blueberry muffin has separate parts we can see, but eventually I might try dissolving the thing in different solvents (water, isopropyl alcohol, ethanol, benzene)… It makes more sense when it’s not a blueberry muffin.

Introduction to the topic

This is an introduction to the vocabulary for those who are new to using the words. When I initially found this video, I thought it was awful and then I became sort of infatuated. In part because they overlay those water droplets coming out of the faucet to keep the little point tops only at the point where they’re attached to the faucet. Bravo.

Here’s a more verbal introduction:

Alright, I am putting soap here again, because surfactants change the solubility of many substances in water. This is something I learned from Dr. Kurt Pennell at Georgia Tech (Civil and Environmental Engineering) because when we want to get certain insoluble (“immiscible” is another word for liquids) substances out of groundwater we can use surfactants. The various contaminants (e.g., gasoline, dry cleaning solvents, coolants) “partition” into “stuck to soil,” being in the gas phase (you can smell this stuff, right?), and being sort of dissolved in water. Surfactants make more of it “dissolve,” so we can pump more of it out…but then you get the surfactant itself down there. It’s tricky. Not unlike the Deep Horizon oil spill problem we experienced in 2010. More on that in the response portion.

Experiencing the Science Part 1: Oil soluble vs. water soluble

Let’s focus on some things dissolving in oil and some things dissolving in water, but soap being a sort of Trojan horse that gets oily stuff into water.

Start by just dissolving some stuff in water. Making sweet tea is a good demo because, in the south we make sweet tea by adding sugar to hot tea and then icing it. If you bring us unsweet iced tea when we want “sweet tea,” it’s no good to us. You can’t get enough sugar into cold water to make “sweet tea.” Sweet iced tea is a super-saturated solution.

I did this salt dissolving thing for the floating ice lesson:

As of this writing, we’re still working on how much sea salt we can get to dissolve in our little ice cube tray. I’m using hot water and stirring with a toothpick. I like the sea salt because we don’t have to “measure,” we can count. Also, we can practice multiplication tables, which is apparently critical at this stage of my child’s mathematical career. We end up talking about all the things that impact solubility: temperature, surface area, stirring, etc.

Okay, now then, what’s more oil soluble than water soluble? Whatever you prefer to try. Maybe even compare oil to water using the salt demo (this makes it an experiment). By the way, people suggest making herb ice cubes you can store, but maybe it’s better to put them in oil? Discuss.

Experiencing the Science, Part 2 (Soap again): This time it’s about solubility.

Talk and talk and talk about what’s in the water at which stage and what that says about solubility. You know what else is cool? Tie dye and the tie dye fixative. What the bleeb is that stuff!?!

https://www.thespruce.com/set-and-stop-fabric-dye-bleeding-2146657

Responding to the science

Multisensory

We can feel how gritty undissolved salt can be. When I use my neti pot, I stir it with my finger. Try that. Use different temperatures of water.

That cooking demo is going to smell amazing. Should we try using our noses to determine how well aromatics dissolve? Maybe even our taste buds? We can try the ice cube experiment I mentioned above: Put herbs into ice cube trays and then cover some of them in oil and some of them in water. Then maybe smell the melted liquid. Maybe use it to make fancy popsicles.

Creative

Watercolor painting just keeps being interesting for experimenting with water. Solubility can be addressed with masking fluid, which is non-polar, using soap in your watercolor, putting salt on your watercolor…

There are questions to address about where the pigment is soluble also. When I googled “using soap with watercolor paint,” lots of funny interesting techniques came up.

What, for example, is gum arabic and why is it necessary for making watercolor paints out of pigments?

https://www.naturalpigments.com/artist-materials/water-based-paint-pigments

Check out the different solvents you use for different types of paint. Why?

Verbal

I promised, and now I will deliver: Check out that Deep Water Horizon oil spill controversy around surfactants. Holy bajoly.

Analytical

This is an excellent place to practice the 5×5 replication technique suggested by IB teachers the world over (it can be 3×3 or 2×2 for the beginning practice, but why?):

Make 5 different “treatments” or test categories or “concentrations” in this case: Look at that ice tray above and see how I did 0, 1, 2, 3, 4 grains of salt for the same volume of water. That’s 5 different concentrations. It’s your “independent variable” or your “test variable.” People call it the “I change” variable because you, the researcher made intentional decisions about how to change it.

Now “replicate” each concentration. My ice tray is a 5×4, so it only does 4 replicates. The idea now would be to measure something that you’re curious about. “How does salt concentration impact…?” You can try dog preference by asking how many times each cube gets carried away or eaten (it’s not too much salt for dogs at this concentration, but if you kept going up it would be unethical and unkind). You can try how long it takes to melt. I was going to try asking how well the ice cubes float, but so far all of them float. Apparently this works better if you make all the ice cubes out of fresh water and then make the water they’re floating in salty… Anyway, the thing you measure is your “dependent variable,” presumably because it might depend on the thing you changed.

The idea here is that you can combine your results and do statistics because you’ve replicated the data. You have five values of your independent variable and 5 replicates of the measured value. Try graphing the results individually and then, if you’re into math, try graphing averages with maximum and minimum values indicated (this is the range).

If all of this sounds confusing and overwhelming, think about how you would like to “analyze” the data. What makes sense to you in terms of describing/summarizing what you found?