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Thanks to Ridge Family Center for Learning for
having us recently!!
We encourage your interest in all things
scientific. We've described a few of the things we do in our
school science assemblies that are safe for you to try. Please be
sure to get adult help from your family or teachers before trying
any of these, and be sure to follow proper safety
procedures, including wearing safety glasses, when trying any of
these science demonstrations.
Pop Can Collapse
Description
A can is collapsed by atmospheric pressure and nothing else!!
Materials
Procedure
Pour two teaspoons of water into an empty pop can. Boil the water by
putting the can on a hot plate or over a candle. When steam begins
to leave the can, using gloves or tongs, turn it over quickly so the
hole is "down" and plunge it into the bowl of cold water. The steam
will condense, leaving a partial vacuum within the can. The can will
collapse rapidly due to air pressure pushing on the sides of the
can.
Theory
As the water inside the can turns to steam, the steam pushes the air
out of the can. When the can is plunged into cold water, the steam
condenses back into water, resulting in a partial vacuum inside the
can. With little or no air in the can, equilibrium is lost and
14.7 pounds per square inch of atmospheric pressure presses on the
can, causing it to collapse.
Pocket Rockets
Description
A film canister is launched using carbon dioxide to propel it.
Materials
Procedure
Put a level teaspoon of baking powder (not baking soda) in a film
canister. The canister has to be one of the white plastic canisters
from Fuji Film, not the black ones with the gray lid. To the baking
powder add one quarter film canister of water and quickly place the
lid on the canister. Shake well and place it lid end down on a flat
surface. After a few seconds the canister will be blown into the
air, leaving behind a splatter pattern similar to that seen on
launch pads when rockets blast off. This is best done outdoors or in
a room with a smooth floor and a high ceiling (like a gymnasium).
Theory
The chemical reaction between the water and baking powder causes
carbon dioxide to form, which builds up enough pressure to “pop” the
lid from the film canister and cause it to shoot into the air. Baking powder is a solid mixture that is used as a chemical
leavening agent in baked goods. It can be composed of a number of
materials, but usually contains baking soda (sodium bicarbonate, a base), cream of tartar (potassium bitartrate, an acid),
and cornstarch (an inert filler). When you
add water to baking powder, the dry acid and base go into solution
and start reacting to produce carbon dioxide bubbles.
Baking soda, has the chemical formula NaHCO3. Cream of tartar has the formula KHC4H4O6. Carbon
dioxide has the formula CO2. The chemical reaction when water is added to baking
powder is:
NaHCO3 + KHC4H4O6 ----> KNaC4H4O6 + H2O +
CO2
Gas Bags
Description
A chemical reaction between two solids creates a gas to fill up
a plastic bag.
Materials
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One gallon size Ziplock bag
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5 teaspoons of baking soda
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5 teaspoons of calcium chloride
(ice melt)
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6 teaspoons water
Procedure
Put the baking soda and the calcium chloride into the Ziplock
bag. Add the water and seal the bag. Move the bag around in your
fingers to mix the materials together. You should hear a fizzing
noise, and the bag will fill up with carbon dioxide gas.
Theory
A chemical reaction occurs between the calcium chloride and the baking
soda in which a double replacement reaction takes place. The two
solids switch partners and form a new substance--the precipitate
calcium carbonate. As the precipitate is formed, the bicarbonate
breaks down first to make hydrogen ions, an acid. This acid then
converts some of the bicarbonate to carbon dioxide gas which begins
to blow up the plastic bag. You will usually notice a warm spot on
the bag - this is where there is still a lot of calcium chloride,
which gets warm from an exothermic reaction (a reaction which
releases energy, in this case, in the form of heat).
If the two solid materials are
placed in separate corners of the bag without any mixing, when the
water is added, as part of the chemical reaction between the two
solids, a change in temperature can be felt--in one corner of the
bag, an exothermic reaction causes the calcium chloride gets warm,
while in the other corner an endothermic reaction makes the baking
soda gets cold.
Calcium chloride + baking soda
(sodium bicarbonate) = calcium carbonate + sodium chloride +
hydrogen ions
CaCl2 + 2 NaHCO3 ---> CaCO3 + 2 NaCl + H+ ions
Hydrogen ions + sodium bicarbonate
---> carbon dioxide + water + sodium ions
H+ ions + NaHCO3 ---> CO2 + H2O + Na+
Hovercraft
We made our hovercraft following these
plans by William J Beaty.
Click on this link: http://amasci.com/amateur/hovercft.html
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