Alchemy 101
Objective
You will use qualitative analysis to decipher the truth behind an alchemist’s claim of
being able to turn copper into silver, then into gold.
Introduction
Many of the processes and substances that we know today were discovered by the
alchemists. They discovered alcohol, hydrogen, phosphorous, and gunpowder. They
also discovered the processes of distillation, evaporation, and filtration.
Alchemy was a strange mixture of science, medicine, magic, astrology, religion, and
philosophy. One of the main goals was to change a base metal (such as lead) into
gold. Producing gold would not only make them rich, but alchemists felt it would be a
major step towards finding the elixir of life – the liquid that would make one immortal (or
at least prolong life and give one good health). Eventually this was renamed the
philosopher’s stone. (Natural science was once called natural philosophy.)
Now let’s take an imaginary trip back to the Middle Ages when knights were bold,
castles were to be stormed, fair ladies rescued, dragons slain (well, maybe we are
pushing it on the dragon bit), and alchemists were at work. The King has just called
you for advice. It seems the local alchemist has devised a way to make copper into
silver, and then turn the silver into gold! The King wants you to perform the
experiment, test the gold, and give him your recommendations. Does he patent the
process and reward the alchemist -- or hang him as a cheat?
The alchemist’s equations are:
(The following table might be helpful as you translate the equations into modern
English.)
LAB ONE
Alchemy 101
Now it’s up to you. Remember the King is very gracious in his rewards for good work
and harsh in his punishments for wrong answers. Base your conclusions on good
scientific thinking.
During this experiment, you will need to read and record experimental data correctly.
You will need to:
•
Read, record, and report data according to good scientific protocol
•
Report calculations in the correct number of significant digits
•
Draw and support your conclusions with your experimental data.
Skills:
Quantitative Measurements
Lab equipment: Scales, Burners, Vernier Calipers,
Handling of chemicals
Scientific process
Calculations
Data recording and observations
Materials & Equipment
Evaporating Dish
Zn metal
3M Aqua alkali
Sal and acetum solution
Ring stand and iron ring
Tongs
Bunsen burner
Distilled water
Pennies
Wire gauze
Procedure
1. Place a small spoonful (about 0.6-0.7 g) of zinc (Zn) in a large
evaporating dish. Add enough aqua alkali (3M NaOH) to cover the zinc
and gently heat with a Bunsen burner until it begins to steam.
2. Using tongs, clean a copper (Cu) penny by carefully immersing it in a
solution of 2.5 g sal (salt) in 15 mL of acetum (vinegar) in an
evaporating dish for a few seconds. Remove the penny with the tongs
and place in a small evaporating dish filled with water. Then carry it to
the sink and rinse thoroughly using running water.
CAUTION:
Hot NaOH
solution is very
damaging to
your skin.
CAUTION:
Acetic acid is
corrosive.
3. Weigh the dry penny. Note the feel of the coin.
4. Using tongs, immerse the clean copper coin in the steaming aqua alkali solution.
In less than a minute, large bubbles of hydrogen gas will start to escape
and the coin will change to silver right before your eyes! You may stop
CAUTION:
The coin is hot –
heating and when it cools, remove, wash, dry, and weigh the coin. You
don’t burn
yourself. Cu will
melt so don’t
heat it too long.
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LAB ONE
Alchemy 101
must take the dry coin to your instructor so he can initial your report sheet.
5. Use tongs to hold the coin in the outer cone of a Bunsen burner. Gently heat for just
a few seconds and “poof,” the coin will change from silver to gold. Heat the coin for
1-2 seconds after the change and then cool it by immersing it in water.
6. After it cools, dry and weigh the coin. You must again take the dry coin to your
instructor so he can initial your report sheet.
7. (Aside: If you wish to preserve your coin at either the silver stage or the gold stage,
you can coat it with clear nail polish or by spraying it with a coat of clear acrylic
varnish or lacquer. To do this, you must bring the nail polish or acrylic spray; to save
a silver coin, you must have an extra penny, too.)
8. This is a short lab; complete all work and turn in your report today before leaving.
Otherwise, the King will have your head (and your grade). You are relieved from the
type-written requirements, but must still conform to sound logic and thought.
Cleanup
Wash the remaining zinc solution into a large beaker of water marked “Zn waste” by
dipping the evaporating dish into the water. Clean your lab area before being signed
out by your lab assistant (be especially careful of NaOH that may have spattered out
while you were heating).
Calculations
9.
Calculate (and show calculations) an estimated weight for the coin at the silver
stage and at the gold stage by using the density of the metal and the volume of the
coin. (Volume = π r2 t; r = radius (diameter ÷ 2); t = thickness)
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LAB ONE
Alchemy 101
Post Lab Questions
1. Why did the copper change to silver? (Did it, or did it just look like it was silver?)
2.
Why did the heating cause it to change to gold? (Standard disclaimer applies.) Was this a
chemical change?
4
LAB ONE
Alchemy 101
Report: Alchemy 101
Name
Lab Partner(s)
Section
Date performed
Data
Weight of the original coin
How does the coin feel?
Weight of the silver coin
How does the silver coin feel?
Instructor's Initials
Weight of the gold coin
How does the gold coin feel?
Instructor's Initials
DECISION TIME:
Do you tell the King the coin was really changed into
silver and then into gold?
□
Yes
□
No
Please give a short explanation of what occurred; use observations, facts, etc.
to support your hypothesis.
5
LAB ONE
Calculations
Alchemy 101
(detailed calculations are attached)
Rather than lose your head, use your head. Consider the densities of the
three coins. (Remember to show your calculations!)
Note: the densities are :
Thickness
Diameter
Volume
Calculated Weight
Actual
Weight
(based on your lab
measurements)
Copper Coin
Silver Coin
Gold Coin
6
Cu
9.0 g/cm3
Ag
10.5 g/cm3
Au
19.3 g/cm3