Science Bus
Summer 2007
18-19 September 2007
Paul SanGiorgio and Nicholas Breznay
Chemical Reactions
Goals: The students will learn that chemical reactions take place when one ore more chemicals
(or “thing” for the young ones) transforms into one or more other chemicals. They will learn to
define and identify reactants and products. They will write simplified chemical reactions and
descriptions of three fun chemical reactions.
Materials
For Introduction:
2 Packages Mentos® candy
A few 2-Liter bottles of Diet Coke (1-Liter bottles?)
For Penny Experiment:
60 or so Pennies from before 1982
A small bottle of white vinegar
A few teaspoons of table salt
A few clear plastic cups
Paper towels
A couple of stainless steel screws or nails
For Baking Soda / Vinegar Experiment:
A small bottle of white vinegar
Box of baking soda
A bunch of clear plastic bottles
A bunch of balloons
A spoon to measure out baking soda
Lesson Worksheet
Introduction
As stated above, the goals of this lesson are really simple: get the kids to understand that in
chemical reactions there are reactants and products. To introduce this lesson, we will just talk
very briefly about what a chemical reaction is (try to get the kids to come up with ideas, if
possible), and then we will move quickly onward to a very exciting demo (which the kids might
have seen before, but is still fun).
Assemble kids outside of the classroom. Prepare demo by putting 5 Mentos in a rolled-up piece
of paper, and punching a suitably sized holed in a replacement Coke bottle lid. Unscrew the lid
on a Coke bottle, drop in Mentos and (if possible) screw on the hole-punched lid. Shake if
necessary. Perform demonstration a few times (different hole sizes? numbers of Mentos? Coke
bottle sizes?). Return to classroom. Using the whiteboard, ask for suggestions for the before and
after “blanks” for this reaction (i.e. ____ + ____  ____ + ____ type of thing.) If need be, point
out that the Coke is “flat” after the reaction. How has it changed? Point out that the Mentos is
still Mentos, just in a different form. (Have a volunteer compare used and unused. Look same?
Taste same?) After listing ideas for the before and after, fill in “Bubbly Coke + Mentos  Flat
Coke + Mentos + Gas. (Can anyone think of how we could test what is happening? Combine
Mentos with another type of soda? Use other candy with Diet Coke?) Discuss as warranted.
After doing the Diet Coke & Mentos experiment, and completing the simplified chemical
reaction equation on the whiteboard, pass out the worksheet (which has blank simplified
reactions for the other two demos) to the kids. They will attempt to fill this out at the next two
stations. If there is time at the end, they can compare with the rest of the class. Split the kids up
into groups, and have the kids work on one of two experiments, pennies or baking soda &
vinegar. We should have enough materials that each group can work on whatever they want at
any pace. Switch to the other experiment when you are done with the first.
Penny Experiment
In this lesson, the kids will attempt to clean some very ugly pennies. We will be using pre-1982
pennies, as they are primarily copper (newer ones are just copper coated zinc). First off, ask the
kids why the pennies are dirty. Sure, there’s some dirt on them (maybe you could try wiping
them off), but what about the color of the pennies? Do new pennies look different? Try to
explain that this is due to a chemical reaction which takes place when the pennies are exposed to
air. The longer the penny has been in circulation, the more it is exposed to air and the more
brown and dull it looks (generally speaking). Lots of things can affect this, as different pennies
always behave differently, but this isn’t too broad a generalization.
Explain that instead of trying to reverse this process, we are just going to try and remove the
“dirty” or “oxidized” part on the outside of the penny and reveal a cleaner layer underneath.
Add a teaspoon of salt to ¼ cup of vinegar in a clear plastic cup. Stir until the salt dissolves.
You can explain that even this is a chemical reaction! Once the salt has dissolved, dip a penny
halfway into the solution. Hold it there for about thirty seconds, and pull it out to see what
happened. It should look a bit cleaner.
Take a bunch of pennies and toss them in. Let them sit for a few minutes, and try to get the kids
to fill in the left half of the chemical reaction work sheet. Maybe something like dirty penny +
vinegar + dissolved salt -> ???. Once the pennies have been sitting for a few minutes, take them
out put roughly half of them on a paper towel to dry (don’t wipe off the vinegar) and take the
other half and rinse them in water first before drying.
Now, we try to figure out what to put on the right side of the equation. One of the products is
definitely “clean penny”, but what happened to the “dirty penny” stuff (the oxide)? We will
attempt to prove that it exists in the vinegar solution by plating it out onto the stainless steel
screw. Lean the screw against the side of the cup so that half of it is in the solution and half out.
Let it sit for a while (a few minutes). You can go on to the other experiment at this point (if you
haven’t done it) or you can just kill time looking at the two sets of pennies you took out. Are
there any differences? (You should see some green verdigris on the ones that you didn’t wipe.
This is a result of a special oxidation in air).
After removing the screw and inspecting it, you should be able to fill in the right half of the
equation with “clean penny” and “dissolved copper” (and “vinegar” and “dissolved salt?”).
Baking Soda & Vinegar Experiment
All the kids have probably seen this about a thousand times now, but it’s still fun and they still
enjoy it. We will be doing the classic baking soda and vinegar experiment, but with a slight twist.
We will be using plastic water bottles to contain the whole thing, which allows us to keep all the
products and reactants together, and therefore identify them easily.
Do a quick demo of the experiment by placing a small amount of vinegar in the water bottle and
then dropping in a small scoop of baking soda. This should bubble nicely (not too nicely, you
don’t want a mess). Try to get the kids to fill out the “reactants” side of the chemical equation
with “baking soda” and “vinegar”. Ask them what should go on the products side? How do you
know what it produced? It definitely made a lot of bubbles, but that’s not very scientific. Try to
get them to figure out how you can contain the products so that you can analyze them.
The idea here is to use the balloon to catch the gas that is made. Put the vinegar in the bottom of
the bottle, but place the baking soda into the balloon. Then, seal the bottle with the balloon and
dump the baking soda into the vinegar. The reaction (if appropriate amounts are used) should fill
the balloon. Now, have the kids fill in the product side with “gas” and “muck at the bottom” or
something similar. Try to get them to reason how they would figure out what the muck at the
bottom is, or what type of gas is in the balloon. This is pretty tough, but maybe the older kids
will have some ideas.
If you have extra time, try adjusting the amount of baking soda/ vinegar and seeing the effects on
the size of the balloon. Is the amount of gas produced proportional to how much you start with?
Chemical Reactions Worksheet
Group Members:
REACTION 1:
MENTOS AND COKE
What was there before:
Reaction:
What was there after:
___________ + ___________
REACTION 2:
ACID + PENNY
What was there before:
Reaction:
What was there after:
___________ + ___________
REACTION 3:
 ___________ + ___________
BAKING SODA + VINEGAR
What was there before:
Reaction:
 ___________ + ___________
___________ + ___________
What was there after:
 ___________ + ___________