March 2, 2011
by: Carl Ahlers
Next time you step onto the beach, bend down, grab a handful of sand and admire the fact: By mass 47% of what you hold in your hand is the element silicon. The rest is simply oxygen. Remarkable!
Silicon is the second most abundant element in the earth’s crust (27.7%) – only oxygen beats it – and can easily be extracted from white sand (SiO2) in a spectacular reaction in the school science laboratory.
In Thermite reactions metal oxides react with aluminum to produce the molten metal. These redox reactions require substantial activation energy to get going and are highly exothermic.
They have been used industrially for welding (even under water), the preparation of metals from their oxides (reduction) and the production of incendiary devices. The process is initiated by heat but then becomes self-sustaining. Read the rest of this entry »
June 13, 2010
by: Tami O’Connor
When two 1-pound, 2-inch diameter, chrome steel spheres are smashed together, enough heat is generated at the point of contact to burn a hole in ordinary paper! This dramatic demonstration has been a favorite of students in every grade for as long as I have been teaching!
There are a few considerations when allowing students (especially younger ones) to conduct this activity on their own… First, the spheres are pretty heavy, so if they were either dropped on a foot or onto a nice tile floor, the result would not be good. Also, be sure that the only thing between the spheres is paper or aluminum foil. Fingers caught between the colliding spheres would not be happy. Finally, all participants should wear safety glasses, as it is not unusual for a small piece of paper to fly off after the spheres collide.
The Procedure for Smashing Steel Spheres:
Have an assistant hold the top edge of a piece of regular white paper vertically. Hold one sphere in each hand on either side of the paper. Quickly move the spheres together until they collide against the paper. If they do not burn a hole in the paper the first time, try again and move the spheres together more quickly. Examine the hole in the paper. You will see that the areas around the edges of the hole are actually singed, and you will smell the burning paper! Read the rest of this entry »