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

This video show the chemical reaction between phenol red liquid, sodium bicarbonate (white powder), and calcium chloride (white bits). There is a chemical reaction that produces carbon dioxide gas which inflates the bag, heat, and color changes to yellow. ScienceFix.com producer: Darren Fix

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

High School Chemistry Mass change during a chemical reaction Iron wool/steel wool is placed on an electric balance and ignited using a burning splint. The change in mass can be observed as the iron wool burns. Students should be able to explain why the mass reading on the balance increases at the end of the experiment.

A good experiment for youngsters.Ask first: Does iron burn? 'No' they say. Ask: When things burn do they get heavier or lighter? 'Lighter' they say. Use iron wool, not steel wool and get the finest grade you can get from the ironmongers.

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

Clicking the metal disk inside causes a few of liquid sodium acetate molecules to flip to a crystallized state causing a chain reaction. The solidifying liquid creates 130°F of exothermic heat in the process. You can boil the package to return the crystallized sodium acetate back to a liquid form for reuse.

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

Professor Jim Holler of the University of Kentucky demonstrates the concept of limiting reactants with magnesium and hydrochloric acid.