Vanishing Volume

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.

Pressure Cooker

boiling water in a low pressure syringe

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.

Marshmallow Magic

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.

Water Flowing Uphill

A candle is placed in a crystallizing dish containing water and lit. A beaker is placed upside-down over the candle. The candle will eventually go out and the water level in the beaker will rise.
CxHy­ (wax) + (x +y/4)O2 (g) → x CO2 (g) + (y/2)H2O (l)

Shrink A Balloon

shrink a balloon liquid nitrogen

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.

Pepper in Water

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.

Make Water A Gel

sodium polyacrylate forms a gel with water

This demo uses sodium polyacrylate, a super absorbing polymer found in diapers, to turn water into a gel. The sodium polyacrylate has carboxylate anion portions and sodium cation portions. Water is attracted to the sodium ions, thus it enters the polymer through osmosis and the polymer swells and the sodium carboxylate is ionized. The anionic carboxylates on the polymer repel each other, causing the polymer to swell, trap the water, and form a gel. When NaCl is added the increase of electrolytes (ions) in the water shield the repulsion of the carboxylates, thus contracting the polymer and expelling the liquid water.

Collapse a Soda Can

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.