Reaction in a Bag

Description:  This video shows a chemical reaction of sodium bicarbonate (baking soda), calcium chloride (road salt), and an indicator phenol red. The chemicals react to form calcium carbonate, sodium chloride, and carbon dioxide gas. This changes the pH inside the bag resulting in a color change in the phenol red. As much air as possible should be removed from the bag as possible to show the production of the gas. This could be used as an example of chemical reaction that releases energy (exothermic). Since the bag is sealed it could be massed before and after to show the conservation of mass (atoms). This phenomenon was submitted by Brian Babulic.

Web Resources:  Reaction in a Bag - Flinn Scientific, American Chemical Society - Explanation

Burning Steel Wool

Description:  This is an excellent phenomenon to discuss chemical reactions and the conservation of mass. Steel wool is burned leading to an increase in mass. When doing this in class show the students the burning steel wool to begin with and have them predict the change in mass. Most students believe the mass will either increase or decrease. This phenomenon can be used at the beginning of a unit on chemical reactions and students can investigate their individual models. (e.g. mass comes from fire, oxygen, carbon, etc.)

Web Resources:  Combustion of Iron Wool - CFNS Experiment 36

Reusable Heat Packs

Description:  This phenomenon uses a supersaturated solution of sodium acetate. Clicking the metal disc releases a small number of crystals of sodium acetate which act as nucleation sites for the crystallization of the sodium acetate into a hydrated salt. Energy is released from the crystal lattice. The heating pack can be placed in boiling water and the sodium acetate can be dissolved again. This phenomenon shows how bond energy can be released.  It also shows the importance of chemical engineering and could lead to a section where students design a device (or application) of their own.

Web Resource:  Chemical Heat Pack - Wikipedia, Snappy Heat - Amazon

Limiting Reactant

Description:  In this phenomenon both magnesium metal and hydrochloric acid are limiting reactants.  I have used this in a chemistry class, framing it as "The Case of the Mixed Up Masses".  I tell them that I added varying amounts of magnesium metal but I forgot to label the flasks.  If done correctly they should get the curve seen below.  I learned about this on the NSTA Resource page.  

Web Resource:  NSTA Stoichiometry Balloon Race