This is a hands on activity that demonstrates how chemical reactions change the properties of a substance. In this case, borax (sodium borate) changes the sticky properties of Elmer’s glue, to make a fun to play with putty. Elmer’s glue is polyvinyl acetate, and when sodium borate is added to it, a cross-linked polymer is created giving the glue very different properties that make for a fun activity for students!
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.
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.
Candle wax is flammable as a vapor, so a candle can be relit by igniting the smoke trail of a recently blown out candle, which contains wax vapor. This can be used to demonstrate how caution needs to be taken with flammable vapors.
The reaction of sodium thiosulfate and hydrochloric acid produces colloidal sulfur which clouds the solution. As the sulfur concentration increases, shorter wavelengths are scattered and longer ones pass through, this causes an increase of reddish color to appear on the overhead.
Na2S2O3 + HCl → 2NaCl + SO2 + S + H2O
Anthocyanin, which is found in red cabbage, is a natural indicator that can be easily extracted.
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.
This demo picks up an ice cube without lifting it. The salt changes the melting point of the ice cube which “freezes” it to the string, allowing the demonstrator to pick the ice cube up.
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.
This demo has a solution in a flask that changes color from pink to blue to green to yellow to orange as the solution is stirred. The different colors are due to the different oxidation states of Mn.