Soumit par Elise Farmer
Grades: 4th – 6th
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.
Material
Bomb
 Coffee can with
plastic lid and
straw
 Cornstarch
(should be in
the container)
*To the kids
this is
SPECIAL
powder, ONLY
available at the
university
 Scrap paper to
burn
 Lighter
Acid base
reaction
 Clear glass or
cup
 Bromthymol
blue
 HCl
 Tums
 Pipette
 Spoon
Lava lamp
 Vegetable oil
 Vinegar
 Baking soda
 Food colouring
 Pipette
 Clear cups
(enough for
whole class)
 Spoon
Styrofoam in
acetone
 1 glass
 Acetone
 Styrofoam
pieces
Slime
 Bowl
 Wood glue
 Borax/water
mix
 Food colouring
 Film canisters
(enough for the
whole class)
Material to replace
 Scrap paper
 Styrofoam
pieces
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. Acid base neutralisation
- First place the pH indicator (bromothymol blue) in a beaker of water. It should be light blue
- Add a few drops of HCl. The solution should turn yellow.
-
Crush up some Tums and add them to the solution. After a few minutes, the solution should be light
blue again.
3. Lava lamp
- Place students in groups of 2 or 3 and give each group a clear cup.
- Fill each cup to about ¾ with vegetable oil, then add vinegar (about 1/8 of the cup) and a few drops of
food colouring.
- Add a spoonful of baking soda and watch what happens.
4. Styrofoam in acetone
- Pour some acetone into the glass, to about ¼ of the glass full.
- Put the Styrofoam in the cup, and watch it dissolve.
5. 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.
Safety
Be careful with the combustion reactions, the fire is very real! If you get chemicals on your hands, make sure
to rinse them well with water. Be careful with the HCl, the solution is quite strong and can burn.
Atelier
What 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 ---- 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!
Acids, bases, and the pH scale
The pH scale measures the acidity of a substance; it runs from 1 to 14 where 1 is the most acidic and 14 is
the most basic. Water is a neutral substance and is therefore right in the middle of the scale with a pH of 7.
Stronger acids have lower pH levels than weaker ones, while stronger bases have higher pH levels than
weaker bases. Some common acids that are used every day are citric acid (found in lemon juice), acetic
acid (found in vinegar), sulfuric acid (found in batteries), and carbonic acid (found in pop).
Just by looking at a substance, we usually can’t tell if it’s an acid or a base. For this reason, we use pH
indicators. There are a variety of different pH indicators: some are pieces of paper (litmus paper) that
become different colors when immersed in an acid or base. Others are liquids that change color depending
on whether they’re added to an acid or a base.
Hydrochloric acid (HCl) is a strong acid found in the stomach. Special mucus linings protect the stomach wall
from the HCl. When you eat food that’s too acidic, the acid content in your stomach rises too much and you
get heartburn. This is because the walls of your esophagus don’t have the protective mucus lining and gets
burned. At this point, you need a base to neutralize the acid. Neutralization takes place when an acid and
base are mixed together and always produces water (a neutral substance) and a salt. A common base that
neutralizes an excess of acid is an antacid such as Tums.
2. Demo
- Place the pH indicator (bromothymol blue) in a beaker of water to indicate the pH of a neutral
substance. The water will look a pale blue; this tells us that for our indicator, the blue colour means
neutral.
- Add 1 or 2 drops of HCl to the water. This should turn the solution a bright yellow. Since we know
the solution is now acidic, our indicator must mean that yellow is acidic.
- To neutralize the solution Tums are added (after grinding them up, as our teeth would do) and the
solution should turn a pale blue. What does blue mean? Neutral!
Note that now, we know exactly how our indicator works; we can take our observations and test any
substance we want, and will be able to tell if it`s acidic or neutral.
Density
Since we can`t see molecules, it can be really hard to tell them apart. One property that we can use to
separate them is density; basically, we ask which one is going to be heavier if we have the same amount of
each. Think about a pillow full of feathers (yay!) and a pillow full of bricks (ouch!), assuming the pillows are the
same size. Whichever one is heavier is also more dense, and clearly it`s going to be the bricks.
3. Lava lamp
- Place students in groups of 2 or 3 and give each group a clear cup.
- Fill each cup to about ¾ with vegetable oil, then add vinegar (about 1/8 of the cup) and a few drops of
food colouring.
- Add a spoonful of baking soda and watch the lava lamp go!
What happens?
Lots of people have seen the baking soda and vinegar reaction before when making volcanoes: sodium
bicarbonate (a fancy word for baking soda) and acetic acid (an even fancier word for vinegar) react to
produce lots and lots of bubbles. These, like all bubbles, contain a gas known as carbon dioxide. This is the
same gas that we breathe out, and it happens to be denser than the normal air around us, but it is still less
dense than the oil. Therefore, when the baking soda and vinegar react, the CO2 that is created will go to the
surface to create our lava lamp.
When the gas bubble passes from the vinegar into the oil it pulls a small amount of vinegar with it. Eventually,
when the bubble reaches the surface of the oil and pops, the vinegar falls back through the oil to be with the
rest of the vinegar again.
Why are the bubbles colored? It is because the vinegar and the food coloring are both hydrophilic, which
means they can mix together (they both like water and can mix with water). But, the oil is hydrophobic and
doesn’t mix with the food coloring.
Polymers
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.
4. Styrofoam in acetone
- Pour some acetone into the glass, to about ¼ of the glass full.
- Put the styrofoam in the cup, and watch it dissolve.
What happens?
Polystyrene is a linear chain made up of many units of its monomer, namely styrene. In acetone, the styrene
monomers lose affinity (attraction) for each other, and dissolve in solution (separate).
Depending on what you`re using, there may be some polyurethane present. Polyurethane is also a linear
chain made up of many units of its monomer, namely urethane. The difference is that these linear chains are
attached to each other in different places, making something that looks like a spider web. This is called
cross-linking. (Refer to the drawing on the board, and make some of the AAAAAAAA chains connect to each
other randomly). Because polyurethane is cross-linked, it is far more difficult for it to dissolve in acetone and
so some of the foam fails to melt.
5. 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.
- 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.
What happens?
When borax is added to water in solution, it forms a complex structure called sodium tetraborate B4O5(OH)4-2
2Na+. When a solution of borax is added to common household glue, the tetraborate forms bonds between
partially charged hydrogen atoms of one strand of a polymer and partially negatively charged oxygen (or
nitrogen) atoms of another polymer strand. The resulting mixture is a cross-linked hydrogen bonded polymer.
The substance formed has some unusual properties. If it is shaped into a ball and dropped from a height, it
will bounce like a rubber ball (it is elastic). If left sit on the table, the ball will flatten under its own weight. If a
low stress is applied (i.e. slowly pulling on the material), it will flow and stretch. If it is quickly twisted, it will
tear and shear. But mainly, if left alone, it will form into a jelly-like mass with a shiny surface. These are a
class of properties attributed to a class of substances called non-Newtonian fluids (i.e. materials whose
viscosity [thickness] increases when pressure is applied). The polymer is non-toxic and should be stored in a
plastic bag closed with a tie-top (or else it will become mouldy, yuck).
Wrap-Up
So today we stuck molecules together and ripped them apart, turned dangerous ones into water, found the
line between gases, and made others so excited that they burned and blew up! We didn`t see any of the
molecules themselves, but we know they`re present because we saw their properties through the use of
chemical reactions. That`s what chemistry is all about!