Ron Tuinstra [Illiana Christian High School, Chemistry]
The Concept of the Mole
Ron brought in a roughly square piece of galvanized iron (iron with a zinc coating) about 2.5 cm on a side and 1 mm thick. He weighed and measured the piece, and then removed the zinc from it by soaking it in hydrochloric acid: Zn + 2 HCl ® ZnCl2 + H2 (bubbles) After the chemical reaction had ceased, he thoroughly washed the piece in water, and then dried it. The metallic piece was visibly thinner than it had been.. Our objective was to determine the approximate number of zinc atoms on the piece of galvanized iron, and the approximate thickness -- in atoms -- of the zinc coating. The procedure involves measuring the mass and size of the galvanized iron, before and after the zinc coating is removed. From the masses of zinc and iron, we can calculate the number of moles and atoms of each metal. By using the known radius of the zinc atom and assuming that the atoms of zinc are stacked directly on top of each other in the coating, we can estimate the thickness of the coating.
We took data and made calculations concerning the piece of galvanized iron, as given in this table:
|Length of rectangle||2.5 cm|
|Width of rectangle||2.6 cm|
| Mass of rectangle|
(before acid treatment)
| Mass of iron core / Fe|
(after acid treatment)
|Mass of zinc coating / Zn||0.22 gm|
|Molar mass of Fe||55.8 gm/mole|
|Num moles of Fe in sample||3.9 ´ 10-2 moles|
|Molar mass of Zn||65.38 gm/mole|
| Num moles of Zn|
(in original coating)
|3.4 ´ 10-3 moles|
|Mole ratio: Zn/Fe||0.086|
|Num Zn atoms||2.0 ´ 1021|
|Num Fe atoms||2.4 ´ 1022|
|Mass of Zn / one side||0.11 gm|
|Density of Zn||7.14 gm/cm3|
|Volume of Zn /one side||1.5 ´ 10-2 cm3|
|Thickness of Zn coating||2.4 ´ 10-3 cm|
|Size of Zn atom||2.66 ´ 10-8 cm|
|Thickness of Zn (in atoms)||85,000 atoms|
Chris Etapa [Gunsaulas Academy]
Chris brought in an Energy Ball [http://www.stevespanglerscience.com/product/1406], which she uses for teaching about electrical circuits. The Energy Ball resembles a ping-ping ball, with two metallic contacts on its surface, as well as a battery, a light bulb, and a "beeper" hidden inside. When the contacts are connected, the light goes on and the beeper sounds, signaling that a circuit has been completed! When one of us put our thumb on one of the contacts and our forefinger on the other one, the light and sound again were produced. Next one person touched one contact and another person touched the other contact. Nothing happened -- until the two people touched their hands together -- again! -- light and sound!. We then formed a "human chain" with several people holding hands When the two people at the ends of the chain each touched the contacts as before -- sound and light! When the human chain was broken, the signal stopped abruptly. Remarkable, but how come? Pat Riley and Ben Stark pointed out that there is saltwater on our skins, and electrolyte solutions throughout our bodies, which are fairly good conductors of electricity. A small amount of electricity is conducted by our bodies, completing the circuit and triggering the sound and light from the ball. These human circuits are similar, in principle, to circuits involving metallic wires.
Fascinating stuff, Chris!
Larry Alofs [Kenwood HS, Physics]
A visitor from the Math-Physics SMILE class, Larry showed that flame tests provide a means of identification of materials. He had a supply of small "nasal spray" bottles that contained solutions of various ions and salts, as well as a portable torch. Larry lit the torch, and then he sprayed a tiny cloud of one of the solutions directly into the flame. We could easily see the flame change to a color that was distinctive of the alkali / alkaline metal (lithium, sodium, potassium, calcium, etc) in the solution, which lasted for a few seconds before disappearing. Sodium, for example, produces a yellow-orange flame color; potassium produces red. Every minute or so he sprayed a different chemical into the flame, producing a new color. The effect was especially dramatic when we turned out the lights in the room. These spray bottles produce a fine mist of the solution, which works very well for doing flame tests.
You really set things on fire! Thanks for popping in and showing us how to do this, Larry.
Notes taken by Benjamin Stark