AN EXPERIMENT IN ALCHEMY:
COPPER TO SILVER TO GOLD
INTRODUCTION
One of the goals of the ancient alchemists was to convert base metals into gold. Although this goal was never
attained by chemical methods, the alchemists were able to perform many color changes to make metals resemble
gold. The introduction of alchemy to the west came in the 8th Century when the Arabs brought it to Spain. From here it quickly
spread to the rest of Europe.
The Arabian belief was that metals are made up of mercury and sulfur in varying proportions. Gold was seen as the perfect metal and
all others were less perfect, an idea popular among western alchemists. It was a very popular idea indeed, that these lower metals
could be transmuted into gold by means of a substance known as the Philosophers Stone.
The Stone is also believed to be able to confer immortality, the Chinese name for it being the Pill of Immortality.
In Europe, alchemy led to the discovery of elements and advances in many other chemical processes. Eventually, by the 16th
Century, the alchemists in Europe had separated into two groups.
The first group focused on the discovery of new compounds and their reactions - leading to what is now the science of chemistry.
The second continued to look at the more spiritual, metaphysical side of alchemy, continuing the search for immortality and the
transmutation of base metals into gold.
This led to the modern day idea of alchemy.
Pre Lab:
Coin #1
Date of Penny
Initial Mass
Volume
Density
1. Describe the penny in terms of physical properties.
2. What material is a penny made of?
Coin #2
Coin #3
Procedure:
1. First clean penny by submersing it in vinegar and polishing it with a paper towel. The penny must be
perfectly clean for the reaction to work.
2. In the hood, a sodium hydroxide and zinc solution have already been prepared. CAUTION: DO NOT
ALLOW THE SOLUTION TO ACTIVELY BOIL, HOT SODIUM HYDROXIDE IS VERY
CAUSTIC AND IT MAY SPATTER.
3. Using the tongs, place two copper tokens into the hot solution and continue to heat gently. Almost
immediately, the copper tokens should begin to turn silvery white and small bubbles of gas will fizz from the
solution. Occasionally, using the tongs, rub the tokens into the zinc at the bottom of the beaker and turn the
tokens over. When the tokens have become completely silver, remove them from the solution and immerse
them in a beaker of distilled water. Wash the tokens well to remove any sodium hydroxide and dry them.
4. Weigh the silver tokens and record the mass of each token on your data table.
5. Using the tongs, hold one of the silver tokens by the edges and heat it in the outer cone of the Bunsen burner
flame. Within a few seconds, the token will change color. Heat it for three more seconds and then
immediately quench it in a beaker of distilled water. The resulting gold token can be dried and polished with
a towel.
6. Repeat this procedure with a second penny. Do not heat your third penny.
7. Weigh the gold tokens and record the mass of each token on your data table.
Data Table: Use the correct units!
Coin #1
Coin #2
Coin #3
Mass of clean dry silver
token
Mass of gold penny
Volume of gold penny
Density of gold penny
Change in mass of gold
penny (Initial-final)
Change in mass of silver
penny
(Initial-final)
Analysis Questions:
1. What happens to the copper tokens when they are placed in the sodium chloride/vinegar acid mixture?
2. Describe the changes that occur while heating the copper tokens in the sodium hydroxide-zinc mixture.
3. Is the silver colored coating on the copper token permanent? Does it rub off easily?
4. Is the gold colored coating on the copper token permanent? Does it rub off?
5. Why is it necessary to quench the copper token in water after heating it to produce the color change?
(Note: You may want to try heating a token and allowing it to cool in the air.)
6. Compare the masses you measured, before and after the silver color change, for each of the tokens. How do the masses compare?
7. The density of copper, zinc, silver, and gold are given in the table below. Based on this information, did you
really change the copper token into gold? Explain.
Metal Density in
g/mL
Copper 8.92
Zinc 7.14
Silver 10.5
Gold 19.3
8. One of the goals of the ancient alchemists was to turn metals into gold. How do you think they might have
reacted to this experiment? (Note: The ancient alchemists did not use balances to weigh things.)
9. When the penny turns a silver color, is this a physical or chemical change? Why?
10. When the penny forms a gold color, is this a physical or chemical change? Why?
11. What is the element that gives the penny its silver color?
12. What is an alloy?
13. What alloy did you make?