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

• Bowl of cold water

• Source of heat (hot plate or candle)

• Water

• Tongs or oven mitts

• A clean soda pop can

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

• A white plastic 35mm film canister (Fuji Film Only)

• Baking powder

• Teaspoon

• Water

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 CO_2. 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

• One gallon size Ziplock bag

• 5 teaspoons of baking soda

• 5 teaspoons of calcium chloride (ice melt)

• 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