Summary
Let’s do some chemistry! Through many different experiments and demonstrations, students will get to observe the wonders of chemical reactions, and the interactions between molecules. Students will have the chance to observe different types of reactions, including combustion, polymerisation and exothermic/endothermic reactions.
MaterialBomb
v Coffee can with plastic lid and straw
v Cornstarch (should be in the container) *To the kids this is SPECIAL powder, ONLY available at the university
v Scrap paper to burn
v Lighter / Burning money
v 2:1 water:ethanol mix
v Tongs
v Plate or bowl
v Lighter
v $5 bill (bring one, or get from teacher) / Reaction in a bag
v Ziplocs (enough for the whole class)
v Baking soda
v 2 spoons
v Anhydrous calcium chloride
v Phenol red
v Film canisters (enough for the whole class) / Glow stick (luminol)
v 1 graduated cylinder
v Diluted hydrogen peroxide
v Luminol / Polymers
v Lightning gel
v Wendy’s cup
v Bowl
v Wood glue
v Borax/water mix
v Food colouring
v Film canisters (enough for the whole class)
Material to replace
v Scrap paper / v Ziplocs
Activities
1. Bomb
- Make a little pile of cornstarch in front of the straw, without actually covering the opening of the straw.
- Light the paper on fire and drop it into the container, then put the lid on it quickly.
- Blow into the straw to make the lid pop off and the flames appear. *Make sure you are well below the opening of the container to avoid burning your hair.
2. Burning money
- Dip the money into the bowl or plate containing the ethanol solution, making sure the bill is completely covered in liquid.
- Use the tongs to take the money out of the liquid, and hold it in the air above the table or desk. Make sure it is NOT above the plate or bowl.
- Light the edge of the bill on fire, and watch it burn.
3. Reaction in a bag
- Have the students place the calcium chloride in one corner of the plastic bag, and the baking soda in the other corner, making sure to keep both powders separate.
- Pour a bit of phenol red into the bottom of a film canister, and fill it to about ¾ full with water.
- Have the students pour the phenol red into the corner of the bag with the calcium chloride, take the film canister out and close the bag. Make sure to keep the solutions separated. The solution should get hot.
- Mix in the baking soda with the calcium chloride solution. The solution should get cold.
4. Glowstick
- Turn off the lights and close the shades to make the classroom as dark as possible.
- Pour luminol into the cylinder, to about halfway. Pour peroxide into the cylinder, so it isn’t quite full (you should be using less peroxide than luminol) and watch it glow!
5. Lightning gel
- Put a bit of lightning gel in a Wendy’s cup (or any other non clear cup), just enough to cover the bottom.
- Add just enough water for it to form a gel. If you add too much water, it will just become liquidy, so be careful.
- Once you’re certain the gel is fairly solid, you can surprise the class by putting the cup upside down over someone’s head.
6. Slime
- Put a bit of water in the bottom of the bowl, then add the glue and food colouring.
- Mix well, so the colour becomes uniform.
- Shake the borax solution WELL, until it becomes fairly uniform.
- Pour in the borax/water solution, a little bit at a time, until the glue takes on a slimy consistency. If you add too much borax, your slime will be too hard.
SafetyBe careful with the combustion reactions, the fire is very real! Make sure the money used to burn is completely submerged in the ethanol mix, any dry spot will make it burn for real. If you get chemicals on your hands, make sure to rinse them well with water.
WorkshopWhat is chemistry?
Everything is chemistry. Chemists study the composition of things, and how they react with each other. They study atoms, and chemical reactions.
What is an atom?
Atoms are the tiniest particles that make up a substance. Everything in the world is made up of atoms. Atoms are like puzzle pieces that get together to make molecules, and molecules make up the things that you see.
You can't see atoms and molecules, because they are so small.
- To demonstrate, ask the class how many atoms one drop of water contains. Give them a hint: it starts with a one, and ask them how many zeros there are after that one! The answer is one sixtillion (1 000 000 000 000 000 000 000) atoms!!!!! That's 21 zeros!
But if we can't see the atoms, how do we know they exist? We know, because of something called chemical reactions! Instead of trying to look at little dots in a microscope (boring!), we`ll look at how atoms interact in order to observe and study them. A reaction is when chemical A and B (called “reactants”) come together and interact in such a way to break and re-create bonds to form a new structure. This new structure creates a chemical called C. It’s important to remember that C is something completely new, and is neither A or B.
A + B ----à C
Combustion
The first thing we will look at is molecules that interact to create combustion. See if anyone knows that combustion is just a fancy word for explosion or something burning.
What are the three things we need for combustion? What do you need when you’re making a campfire? Fuel (the wood), oxygen and heat (or ignition; the match or lighter).
In our bomb, the fuel is the “special powder” (cornstarch), the oxygen is in the air, and the heat is from the burning paper we put into the container.
1. The bomb
- Make a little pile of cornstarch in front of the straw.
- Light the paper on fire and drop it into the container, behind the pile of cornstarch, then put the lid on it quickly.
- Blow into the straw to make the lid pop off and the flames appear. *Make sure you are well below the opening of the container to avoid burning your hair.
What happens?
Once we blow inside the straw, the powder comes in contact with the heat and the air over a larger surface area, which is crucial for any chemical reaction. Once the combustion starts, the particles are suddenly very excited. They move in all different directions, colliding into the sides of the can, and into each other. At this point, the pressure inside the can rises considerably. The can is not strong enough to keep all this pressure in, so the top pops off!
2. Burning money
Cars, fires, and bombs use combustion, but liquids such as ethanol are often used in combustion as well. Cars in the Indie 500 use ethanol as a fuel and can produce a flame that can be up to 600ºC. So what can we do with ethanol?
- Dip the money into the bowl or plate containing the ethanol solution, making sure the bill is completely covered in liquid.
- Use the tongs to take the money out of the liquid, and hold it in the air above the table or desk. Make sure it is NOT above the plate or bowl.
- Light the edge of the bill on fire, and watch it burn. Afterwards, the bill should only be a little wet.
What happens?
Ethanol has a lower boiling point than water, so the fire burns off all the ethanol, but once that is done, the temperature isn’t high enough to burn off, or vaporize, the water. So, the water acts as a protective barrier around the money, so only the ethanol burns and not the actual money.
Exothermic and endothermic reactions
An endothermic reaction is one that absorbs energy from its surroundings, causing the surroundings to become colder. Example: Instant snap cold packs.
An exothermic reaction is one that gives off energy to its surroundings, causing the surroundings to become warmer. Example: Dynamite.
3. Reaction in a bag
- Have the students place the calcium chloride in one corner of the plastic bag, and the baking soda in the other corner, making sure to keep both powders separate.
- Pour a bit of phenol red into the bottom of a film canister, and fill it to about ¾ full with water.
- Have the students pour the phenol red into the corner of the bag with the calcium chloride, take the film canister out and close the bag. Make sure to keep the solutions separated. The solution should get hot.
- Mix in the baking soda with the calcium chloride solution. The solution should get cold.
The calcium chloride reaction in this case is the exothermic reaction (it gives off heat), while the baking soda reaction is the endothermic reaction (it takes heat from the environment, making it colder).
Glowsticks
Chemical reactions can also cause energy to be released in the form of light; when the right reagents are mixed, the energy released is pumped into the electrons, tiny particles that circle around every molecule. The energy absorbed and released by these electrons has to go somewhere, and in many cases is converted into light energy, which gets released as visible light. These reactions are useful in making novelty toys and other stuff that glows in the dark.
Chemicals, such as a mixture known as luminol, can be used with peroxide to produce the same sort of glow in glowsticks. The tube of a glowstick encases two smaller glass tubes, one of which contains peroxide and the other contains the luminol. When the glowstick is bent, the two glass tubes crack and the luminol and peroxide mix, exciting the electrons and producing an aswesome glow. To make different colours of glowsticks, you can mix your luminol solution with the powder of a different metal; in our case we used copper, giving us a blue glow.
4. Demo:
- Turn off the lights and close the shades to make the classroom as dark as possible.
- Pour luminol into the cylinder, to about halfway. Pour peroxide into the cylinder, so it isn’t quite full (you should be using less peroxide than luminol) and watch it glow!
- If you turn on the light, you’ll see that the solution becomes a brown colour. Light causes luminol to lose its reactivity.
Why do you keep a glowstick in the freezer?
1) It’s dark, so the luminol doesn’t lose its reactivity.
2) It’s cold and therefore harder for any reaction to take place between the two compounds, as the molecules aren’t moving as fast and colliding as much as they would at a higher temperature (less excitement).
Polymerization
Polymers are very long molecules consisting of small repeating subunits (called monomers), connected by chemical bonds. The term is derived from the Greek words: polys meaning many (mono means one), and meros meaning parts or units. The monomers are linked to each other during a chemical reaction called polymerization.
Draw a few random chains on the board (that are not interconnected), made up of AAAAAAAAAAAAAAA. The single A represents a monomer, but the collection of A represents a polymer. Have the kids stand up as monomers and spin in circles; now link them together as polymers and see how much harder it is to move! This change in chemical properties is reflected in the materials that we see every day; being free to move around makes for liquid-like properties, whereas the restriction on movement solidifies the object considerably. It`s often easier and cheaper to produce chemicals as liquids (usually called solutions because they are a mixture), but we can then combine solutions to make versatile and diverse solids.
5. Lightning gel
- Put a bit of lightning gel in a Wendy’s cup (or any other non clear cup), just enough to cover the bottom.
- Add just enough water for it to form a gel. If you add too much water, it will just become liquidy, so be careful.
- Once you’re certain the gel is fairly solid, you can surprise the class by quickly putting the cup upside down over someone’s head and watching their surprise when the person isn’t covered in a liquid mess.
What happens?
The Lightning Gel is a loosely cross-linked polymer, meaning it`s made up of monomers that are almost ready to become polymers. All they need is a catalyst, in this case water. Although we can`t see the molecules interacting, we see the liquid become solid; clearly, something is restricting the movement of the molecules! The only explanation is that they must be polymerizing, just like when we all linked arms; the water sticks in between the monomers and forces them to create a polymer.
6. Slime
- Put a bit of water in the bottom of the bowl, then add the glue and food colouring.