This is a PlayChem
experiment in which you place yourself in the shoes of the alchemist,
and convert a US penny from a coppery to a silvery and
finally a golden coin.
This is not magic or sleighofhand.
This is real chemistry.
To
do this you will mix
"earth",
"water"
and
"fire".
•
Earth
is the solid (Zn) melted from the inside of a penny.
•
Water is
"Butter of Zinc" solution; 1.0 M ZnCl_{2}.
•
Fire
is heat to create "silver" and convert "silver" to "gold"

To create "EARTH",
you will melt a U.S., 1983 or later, penny.
Make sure the molten zinc falls on the bench top!
Shake gently if necessary to get melt to drop.
Be careful not to burn yourself.
Molten Zn is hot and remains hot for a minute or so! 
The reaction consists of
...
Zn (EARTH),
pennies and 1 M ZnCl_{2}
(WATER).
The mixture is heated to a gentle boil (FIRE).
The pennies turn silver in 1015 min.
Turn pennies over if necessary.
Boil very gently so reaction does not go to dryness. 

BUT have you achieved the alchemist's dream...
converting copper, a base metal, to gold?
Have you really nudged copper two rows down its column in the Periodic
Table?
How can you tell if you can retire now on this newfound
source of riches?
And if it isn't gold, what is it and why did it happen?
Be
Prepared to:
•
Calculate surface area of a coin. Assume a simple cylinder.
•
Area cylinder = (2 p r^{2})
+ (p d t)
r = radius d =
diameter t =thickness
•
Volume occupied by atom in metal =
(MW)/(Density)(6.02X10^{23})
• Thickness of a mass of metal deposited on a surface
• Measure potentials using Logger Pro
How
many layers of atoms plated out?

Assume changes in penny are due to a thin plating of metal

Assume each metal atom plated is a cube. (simple
cubic lattice)

Mass, MW and Avogadro's Number gives Number of Atoms

MW,
Density and Avogadro's Number gives the cube's Volume

Cube root of the cube's Volume gives Length of Side.

The
cube's Side squared gives the Area of a Face.

Area of Face X Number of Atoms gives Total Area covered if atoms are
lined up next to each other one layer thick.

Total Area Covered / Surface Area of three coins = Layers

Length of Side X Number of Layers gives Thickness.

In
doing the above calculations, it is advisable to use units!

There is an easier way to calculate thickness of the plated coating:

Mass of metal plated and density gives volume of metal plated.

Dividing Volume of metal plated by surface area plated gives thickness.
