Chemical reactions: Analysis
Getting Started
Review with students the process of synthesizing a chemical compound--combining two elements to form a new substance. The definition now should include, "Cannot be taken apart by ordinary means" that is, cannot be mechanically separated by a magnet or a sieve or by dissolving in water. The compound is now glued together in a more or less permanent manner.
Is it possible to ever tear apart a molecule? Yes, indeed.
A Simple Demonstration or Student Experiment
Follow these steps:
STEP 1
• 1 tsp of dry yeast
• 75 ml of warm water
• Food coloring (if desired)
Mix these ingredients together so that the yeast is thoroughly dissolved in the warm water.
STEP 2
• Add 1 Tsp of dishwashing soap
• Mix thoroughly
• Pour this mixture into a 250 ml flask
STEP 3
• Pour 75 ml of Hydrogen peroxide into a beaker.
• Place the 250ml flask in a dish pan
STEP 4
• Pour the 75 ml of hydrogen peroxide into the flask
Observe!
Hydrogen peroxide is a molecule written,
H2O2
The yeast acts as a catalyst releasing oxygen from the molecule so that was we end with is
H2O2 ----> H2O + O
The oxygen gets trapped in bubbles from being in the soapy water and we see the result as foam.
Another Analysis Reaction
If you have a chemistry club or access to a high school chemistry lab you could do the following demonstration:
1) Prepare a 50 ml beaker 3/4 full with granular sucrose (table sugar).
2) Find a secure place out of doors to conduct the experiment.
3) Wear safety goggles and safety gloves
4) Pour onto the sugar concentrated sulfuric acid enough to wet the granules. (Sulfuric acid is nasty stuff. You should have experience and proper cautions to use this highly toxic and corrosive material)
5) Watch and wait
6) When it cools it can be hosed off and dried. Be careful to spread baking soda on the surface where the reaction took place to neutralize and left over acid. The resultant chemicals are harmless and can be washed into the lawn or planter.
If you cannot do this in person, watch the following video:
Discussion.
In this case we have a molecule composed of three elements, carbon, hydrogen and oxygen. When we add the acid it disassembles the molecule. If we watch carefully, we see the black carbon form, but also we see steam. The reaction takes the hydrogen and oxygen and forms water (H20). It is so hot that it boils away. We can also smell sulfur--this is from the acid.
This is an analysis reaction that gives off heat as the atoms are pulled apart. We know there is a chemical change because the results of the materials are no longer like the original. Carbon is black and certainly not sweet!