Vanishing Volume

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Written by: Casey Rogers (ChemDemo) on May 31, 2013.

When 50mL of water are added to 50mL of ethanol in a 100mL graduated cylinder, there are only ~97mL of liquid. Ethanol and water molecules are attracted to each other through hydrogen bonding. The two molecules pack closer together with each other than they do with just themselves.

Metamorphic Magic Plastic

Written by: Casey Rogers (ChemDemo) on July 27, 2012.

In this “trash-to-treasure” activity, polystyrene clamshell containers (#6 plastic) are used to make hard plastic art pieces. When polystyrene clamshell containers are produced, the material is heated and stretched into a mold, thus locking the material in an extended state. When this material is heated again, it returns to its unstretched size and shape. This property can be utilized to create a range of crafts, including buttons, key chains, luggage tags and jewelry. If students mass their plastic before and after, this could also be tied to the Law of Conservation of Mass.

Pressure Cooker

boiling water in a low pressure syringe
Written by: Casey Rogers (ChemDemo) on November 16, 2011.

In this demonstration, warm water is placed in a plastic syringe, the syringe is sealed, and the plunger is pulled back causing the water to boil. The water boils because the action of pulling back the plunger increases the volume, thus decreasing the pressure. The boiling point of a liquid is dependent on the pressure of the system, so a decrease in pressure leads to a decrease in boiling point.

Balloon Kabobs

balloon with a skewer through it
Written by: Casey Rogers (ChemDemo) on September 28, 2011.

In this demo, a skewer is pierced through a balloon without popping it. The balloon is made from a rubber polymer. The polymer is made of many long, elastic, overlapping chains, very similar to spaghetti. When a skewer pierces the balloon, these chains are stretched and pushed open to make a hole for the skewer and the balloon does not pop. It is important to pierce the balloon near the bottom & top, where the rubber has the least amount of stress. The polymer is more able to stretch and rearrange, allowing the skewer to pass through.

Marshmallow Magic

Written by: Casey Rogers (ChemDemo) on September 9, 2011.

When a marshmallow is placed in a large capped syringe and the plunger is pushed in, the air in the marshmallow contracts from the pressure. Conversely, if the plunger is pulled back, the pressure decreases causing the air in the marshmallow to expand.

Liquid Nitrogen Ice Cream

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Written by: Casey Rogers (ChemDemo) on July 21, 2011.

Liquid nitrogen is -196˚C and quickly freezes the ingredients into ice cream. The nitrogen boils out leaving deliciously creamy ice cream. The “fog” that we see is condensed water vapor though, not nitrogen gas.

Shrink A Balloon

shrink a balloon liquid nitrogen
Written by: Casey Rogers (ChemDemo) on June 14, 2011.

When a balloon is placed in liquid nitrogen the air inside it is condensed from the cold (-196°C), causing the balloon to shrink. Once the balloon is removed it will regain its size as the air heats up. Liquid nitrogen boils at room temperature. The “fog” that we see is condensed water vapor though, not nitrogen gas.

Shatter a Flower

Written by: Casey Rogers (ChemDemo) on June 14, 2011.

When a flower is dipped in liquid nitrogen (-196°C) it is instantly frozen. Liquid nitrogen boils at room temperature. The “fog” that we see is condensed water vapor though, not nitrogen gas.

Rainbow in a Beaker

densities of sugar solutions layering liquids
Written by: Casey Rogers (ChemDemo) on June 14, 2011.

Sugar solutions that have different concentrations have different densities; the more sugar in a solution the more dense it is. Therefore less dense solutions can be layered on top of denser ones.

Pepper in Water

Written by: Casey Rogers (ChemDemo) on June 14, 2011.

Water has a very high surface tension because of the strong hydrogen bonding between water molecules, which allows the pepper to float on top of the water. When a small amount of soap is added it forms a monolayer on the surface. The monolayer spreads away from the point of contact causing the pepper to move to the edges of the dish.

Mushroom Cloud

dry ice mushroom cloud bubble
Written by: Casey Rogers (ChemDemo) on June 14, 2011.

When dry ice is placed in warm water it sublimes very quickly forming a large amount of carbon dioxide gas. When a bubble is placed over this the bubble grows from the pressure.

M&M Color Wheel

M&Ms in water, candy coating dissolving
Written by: Casey Rogers (ChemDemo) on June 14, 2011.

When M&M’s are placed in water, the outer shell, which is made of sugar, dissolves. The sugar moves from a place of high concentration (the M&M) to a place of low concentration (the water away from the M&M). When the sugar shell dissolves and moves outward, it takes the layer of food dye with it. When more than one M&M is placed into a petri dish the colors do not mix because the concentration of sugar at the interface is approximately the same. Also, around the bottom of the M&M water appears cloudy because the sugar that is dissolved is more dense than the water, so it sinks.

Hot – Cold Water

hot water rises cold water sinks
Written by: Casey Rogers (ChemDemo) on June 14, 2011.

Hot water expands so it is less dense than room temperature water. Cold water contracts so it is more dense than room temperature water. The red hot water rises and the blue cold water sinks.

Dry Ice in Universal Indicator

dry ice universal indicator acid base reaction
Written by: Casey Rogers (ChemDemo) on June 13, 2011.

Universal indicator goes from red (pH 4) to violet (pH10) as the pH of a substance changes. Adding NaOH to water starts the solution off at pH 8-9 (blue). When dry ice is added to water it forms carbonic acid, and lowers the pH, which is the reason for the color changes. The “fog” that we see is condensed water vapor though, not carbon dioxide gas.

Diet and Regular Soda

diet soda floats regular soda sinks coke
Written by: Casey Rogers (ChemDemo) on June 13, 2011.

Diet soda contains artificial sweeteners while regular soda has sugar in it. Artificial sweeteners are so sweet so only a small amount is needed, where as much more sugar is needed to achieve the same sweetness. Because regular soda has more mass in the same size can, it is more dense than the diet soda.

Color Tornado

food coloring tornado in water on a hot plate
Written by: Casey Rogers (ChemDemo) on June 8, 2011.

In this demo, food coloring is added to a stirring beaker of water to create a tornado of color. This could be used as an example of a physical change, or to demonstrate the importance of properly mixing solutions.

Collapse a Soda Can

crushed can
Written by: Casey Rogers (ChemDemo) on June 8, 2011.

When a small amount of water is heated inside the can, steam is produced, filling the can. When the can is inverted into cold water, all of the steam condenses quickly causing the can to implode.

CO2 Bubbles

dry ice soap bubbles
Written by: Casey Rogers (ChemDemo) on June 8, 2011.

CO2 gas from subliming dry ice gets caught in a soapy solution creating a column of bubbles. When the bubbles are popped, the “fog” that we see is condensed water vapor, not carbon dioxide gas.

Camphor Particles

camphor sublimation
Written by: Casey Rogers (ChemDemo) on June 8, 2011.

In this demo, camphor particles are placed in water. They sublime at room temperature which is why camphor’s odor permeates the room so quickly. The gas that forms around the particles propels the particles in random directions. Earwax contains a large percentage of long chain fatty acids which form a monolayer in water, thus ceasing the motion of the camphor particles.

Bending Water

bending water with a balloon, charging by induction
Written by: Casey Rogers (ChemDemo) on June 8, 2011.

When the balloon is rubbed on a pair of jeans, electrons are wiped from the jeans to the balloon, causing a net negative charge on the balloon. The charged balloon is held near a thin stream of water. Charges in the water rearrange so that the positive charges in the water become attracted to the negatively charged balloon, and the stream of water bends. The rearranging of charges is pronounced because water is a polar molecule.