Special Science Teleclass: Chemistry

This is a recording of a recent live teleclass I did with thousands of kids from all over the world. I’ve included it here so you can participate and learn, too! (Click here if you’re looking for the more recent version that also includes Chemical Engineering.)


When you think of slime, do you imagine slugs, snails, and puppy kisses? Or does the science fiction film The Blob come to mind? Any way you picture it, slime is definitely slippery, slithery, and just plain icky — and a perfect forum for learning real science. But which ingredients work in making a truly slimy concoction, and why do they work? Let’s take a closer look…


Materials:


  • Sodium tetraborate (also called “Borax” – it’s a laundry whitener) – about 2 tablespoons
  • Clear glue or white glue (clear works better if you can find it) – about 1/2 cup
  • Yellow highlighter
  • Pliers or sharp razor (with adult help). (PREPARE: Use this to get the end off your highlighter before class starts so you can extract the ink-soaked felt inside. Leave the felt inside highlighter with the end loosely on (so it doesn’t dry out))
  • Resuable Instant Hand Warmer that contains sodium acetate (Brand Name: EZ Hand Warmer) – you’ll need two of these
  • Scissors
  • Glass half full of COLD water (PREPARE: put this in the fridge overnight)
  • Mixing bowl full of ice (PREPARE: leave in freezer)
  • Salt
  • Disposable aluminum pie place or foil-wrapped paper plate
  • Disposable cups for solutions (4-6)
  • Popsicle sticks for mixing (4-6)
  • Rubber gloves for your hands
  • Optional: If you want to see your experiments glow in the dark, you’ll need a fluorescent UV black light (about $10 from the pet store – look in cleaning supplies under “Urine-Off” for a fluorescent UV light). UV flashlights and UV LEDs will not work.
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The Breaking Point

If you’ve ever teetered on the edge of a diving board, you know that the board flexes under your weight.  The heavier you are, the more it bends.  The top of the board gets slightly stretched further than the normal length (tension) while the underside gets slightly shorter (compressed). We’re going to duplicate this without needing to visit the pool.


We’re going to expand on the topic covered in the Tension and Compression section of this article. All you need for this experiment is:


  • a pencil or a craft stick that you don’t mind breaking
  • a pair of hands
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Moon Sand

A non-Newtonian fluid is a substance that changes viscosity, such as ketchup.  Ever notice how ketchup sticks to the bottom of the bottle one minute and comes sliding out the next?


Think of viscosity as the resistance stuff has to being smeared around.   Water is “thin” (low viscosity); honey is “thick” (high viscosity).  You are about to make a substance that is both (low and high viscosity), depending on what ratio you mix up. Feel free to mix up a larger batch then indicated in the video – we’ve heard from families that have mixed up an entire kiddie pool of this stuff!


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Microwaving Soap

soapWhen you warm up leftovers, have you ever wondered why the microwave heats the food and not the plate? (Well, some plates, anyway.) It has to do with the way microwaves work.


Microwaves generate high energy electromagnetic waves that when aimed at water molecules, makes these molecules get super-excited and start bouncing around a lot.


We see this happen when we heat water in a pot on the stove. When you add energy to the pot (by turning on the stove), the water molecules start vibrating and moving around faster and faster the more heat you add. Eventually, when the pot of water boils, the top layer of molecules are so excited they vibrate free and float up as steam.


When you add more energy to the water molecule, either by using your stove top or your nearest microwave,  you cause those water molecules to vibrate faster. We detect these faster vibrations by measuring an increase in the temperature of the water molecules (or in the food containing water). Which is why it’s dangerous to heat anything not containing water in your microwave, as there’s nowhere for that energy to go, since the electromagnetic radiation is tuned to excite water molecules.


To explain this to younger kids (who might confuse radio waves with sounds waves) you might try this:


There’s light everywhere, some of which you can see (like rainbows) and others that you can’t see (like the infrared beam coming from your TV remote, or the UV rays from the sun that give you a sunburn). The microwave shoots invisible light beams at your food that are tuned to heat up the water molecule.


The microwave radiation emitted by the microwave oven can also excite other polarized molecules in addition to the water molecule, which is why some plates also get hot. The soap in this experiment below will show you how a bar of Ivory soap contains air, and that air contains water vapor which will get heated by the microwave radiation and expand. Are you ready?


Here’s what you need:


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Rock Candy Crystals

Crystals are formed when atoms line up in patterns and solidify.  There are crystals everywhere — in the form of salt, sugar, sand, diamonds, quartz, and many more!


To make crystals, you need to make a very special kind of solution called a supersaturated solid solution.  Here’s what that means: if you add salt by the spoonful to a cup of water, you’ll reach a point where the salt doesn’t disappear (dissolve) anymore and forms a lump at the bottom of the glass.


The point at which it begins to form a lump is just past the point of saturation. If you heat up the saltwater, the lump disappears.  You can now add more and more salt, until it can’t take any more (you’ll see another lump starting to form at the bottom).  This is now a supersaturated solid solution.  Mix in a bit of water to make the lump disappear.  Your solution is ready for making crystals.  But how?


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Penny Crystal Structure

penny-structureThe atoms in a solid, as we mentioned before, are usually held close to one another and tightly together. Imagine a bunch of folks all stuck to one another with glue. Each person can wiggle and jiggle but they can’t really move anywhere.


Atoms in a solid are the same way. Each atom can wiggle and jiggle but they are stuck together. In science, we say that the molecules have strong bonds between them. Bonds are a way of describing how atoms and molecules are stuck together.


There’s nothing physical that actually holds them together (like a tiny rope or something). Like the Earth and Moon are stuck together by gravity forces, atoms and molecules are held together by nuclear and electromagnetic forces. Since the atoms and molecules come so close together they will often form crystals.


Try this experiment and then we will talk more about this:
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Laundry Soap Crystals

Can we really make crystals out of soap?  You bet!  These crystals grow really fast, provided your solution is properly saturated.  In only 12 hours, you should have sizable crystals sprouting up.


You can do this experiment with either skewers, string, or pipe cleaners.  The advantage of using pipe cleaners is that you can twist the pipe cleaners together into interesting shapes, such as a snowflake or other design.  (Make sure the shape fits inside your jar. )


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Salt & Vinegar Crystals

We’re going to take two everyday materials, salt and vinegar, and use them to grow crystals by creating a solution and allowing the liquids to evaporate.  These crystals can be dyed with food coloring, so you can grow yourself a rainbow of small crystals overnight.


The first thing you need to do is gather your materials.  You will need:


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Eggshell Crystals

Geodes are formed from gas bubbles in flowing lava. Up close, a geode is a crystallized mineral deposit that is usually very dull and ordinary-looking on the outside.  When you crack open a geode, however, it’s like being inside a crystal cave.  We’ll use an eggshell to simulate a gas bubble in flowing lava.


We’re going to dissolve alum in water and place the solution into an eggshell. In real life, minerals are dissolved in groundwater and placed in a gas bubble pocket.  In both cases, you will be left with a geode.


Note: These crystals are not for eating, just for looking.


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Salt Stalactites

This is a continuation of the Laundry Soap and Rock Candy experiments, so make sure you’ve done those before trying this one.


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Water Glass & Metal Crystals

This experiment is for advanced students. Water Glass is another name for Sodium Silicate (Na2SiO3), which is one of the chemicals used to grow underwater rock crystal gardens. Metal refers to the metal salt seed crystal you will use to start your crystals growing.  You can use any of the following metals listed.  Note however, that certain metals will give you different colors of crystals.


Your crystals begin growing the instant you toss in the seed crystals.  These crystals are especially delicate and fragile – just sloshing the liquid around is enough to break the crystal spikes, so place your solution in a safe location before adding your seed crystals.


After your garden has finished growing to the height and width you want, simply pour out the sodium silicate solution and replace with fresh water (or no water at all).  Due do the nature of these chemicals, keep out of reach of small children, and build your garden with adult supervision.


Here’s what you need to get:


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Charcoal Crystals

Charcoal crystals uses evaporation to grow the crystals, which will continue to grow for weeks afterward.  You’ll need a piece of very porous material, such as a charcoal briquette, sponge, or similar object to absorb the solution and grow your crystals as the liquid evaporates.  These crystals are NOT for eating, so be sure to keep your growing garden away from young children and pets! This project is exclusively for advanced students, as it more involves toxic chemicals than just salt and sugar.


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