Copper to Gold: the Alchemists Dream

Name ______Partner(s) ______Station # ______Block ___ An Alchemist Dream Lab! PURPOSE: To observe the physical changes that take place when a mixture is formed between two metals

MATERIALS NEEDED: Shiny penny evaporating dish tongs or forceps powder zinc 4M sodium hydroxide (NaOH) solution hot plate scale beaker filled with cold water paper towels

PROCEDURE:

** NaOH CAN BURN YOU SEVERLY AND CAN CAUSE BLINDNESS IF IT GETS IN YOUR EYE. WEAR GOGGLES!!! AT ALL TIMES!!! AVOID INHALING THE FUMES!!

1. Wear goggles and take CAUTION in performing this experiment.

2. Don’t blow out the fuse!! So share your hot plate (in the bottom drawer) with a neighboring lab group! Plug in the hot plate.

3. Clean a penny with steel wool or a pencil eraser. Obtain as shiny of a penny as possible.

4. Place 5.0 g of powder zinc into an evaporating dish. Add 15 mL of sodium hydroxide solution (NaOH). Use tongs to place the penny in the dish, and put the evaporating dish onto the hot plate.

5. Turn the hot plate to the medium setting. Heat the mixture GENTLY until it JUST STARTS TO BUBBLE. DO NOT BOIL VIGOROUSLY OR HEAT TO DRYNESS. (This should take about 10-15 minutes.)

6. Carefully stir the mixture with the tongs and turn the penny. Continue to heat and stir gently until the penny becomes covered with zinc and appears gray in color.

7. Remove the penny using forceps or tongs. AND RINSE WITH LOTS OF COLD WATER. IT’S HOT!

8. Polish the penny with a paper towel – observe. Write down your observations

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9. With the hot plate on still on medium, place the penny directly on the hot plate. You will notice a second change. Record your observations.

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10. Continue heating gently for two or three seconds longer, then immediately immerse the penny into a fresh beaker of cold water. After the penny has been cooled for over a minute, pat it dry.

After completing the lab station, clean your lab station. Pour everything from the evaporating dish into a waste beaker. Rinse materials with water and dry them with paper towels. Return all equipment to your drawer. Make sure your lab area is dry and clean! Questions:

1. Complete the following table:

Element Number of Number of Number of Atomic Charge # of Mass Protons Neutrons Electrons Number particles in Number the nucleus 196 79Au 65 2+ 30Zn 8 10 16 29 1+ 65

2. What are the three subatomic particles?

3. Which distinguishes the atoms of one element from the atoms of another?

4. How might we change one element into another?

5. What do you know about the structure of the atom that would support your answer to the above question?

6. Did you alter the penny and truly change it into gold? How do you know?

7. If your gold penny weighs 2.45 grams and the price of gold is currently $44.75/gram, how much is your gold penny worth?

8. The density of gold is 19.3 g/mL. Convert this to lbs/L. (2.2 lbs=1 kg) 9. Are there any tests that we could perform on our penny to confirm or deny that it consists of pure gold? 10. What do you think was covering the penny when it was silver?

11. Pennies have an exterior of copper. The gold color was a blend/mixture of two metals. What were they?

12. Naturally occurring silicon consists of three stable isotopes: Si-28 92.21% abundance Si-29 4.70% abundance Si-30 3.09% abundance

13. Convert 9.03x1023 Au atoms to moles. (Remember 1 mole = 6.022x1023 items)

14. Convert 3.50 moles of copper to atoms.

15. How many moles of water are in 2.44x1023 H2O molecules? CONCLUSIONS: Consult white board discussions below

TEACHER NOTES

White boards can be a wonderful addition to this activity. A discussion of density can follow this lab, as well as a discussion of alloys, physical changes that resemble chemical changes, and atomic structure. Here are possible questions that can guide each discussion, as well as background information to stimulate discussion. Not all of these questions need to be used, and some questions logically follow others, because the answers to earlier questions are given in later questions!

ALLOYS AND PHYSICAL/CHEMICAL CHANGES:

Background information: A Brief History Of The American Penny

The US Abraham Lincoln penny was first minted in 1909. During World War II, copper was a metal in high demand and during 1943 the US treasury decided to stop using copper in the making of pennies. It used mostly zinc instead. Thus, 1943 pennies had a silver color and were sometimes referred to as "silver pennies." Coin collectors usually collect these types of rare coins. If you ever speak to a coin collector, ask about the silver pennies of 1943. However, it was not until 1982 that the US treasury permanently changed the metal composition of the old penny. The new pennies are almost as durable as the old pennies, since the strong copper plating protects the zinc - which is more chemically reactive than copper.

1. What type of substance did you create (element, compound, alloy, etc.)? 2. Did a physical change or a chemical change occur? What evidence do you have to support your conclusion? 3. What could we do to confirm your conclusion (melt the penny down, examine a cut edge under a powerful microscope, etc.)? 4. If we do in fact have an alloy (conclusion you would reach after extensive discussion), What is the probable identity of this alloy? How did you come to this conclusion? 5. How can we confirm that we have an alloy, and not a compound? 6. Does the evidence indicate that you created an alloy of copper and zinc? Explain. ATOMIC THEORY AND STRUCTURE/DENSITY

At the time of 300 B.C., the Greek scientist Archimedes discovered that the buoyant force is equal to the weight of the displaced fluid. He did this in the bathtub. As the story goes, King Hiero had a crown of gold that he thought might be silver. He asked Archimedes to solve the problem. One day when Archimedes was taking a bath he noticed that water spilled out when he stepped into a full tub. His body took up space and displaced an amount of water equal to his body's volume. 'Eureka'' he shouted. He solved the problem. To test if the crown was pure gold, Archimedes got a silver bar and a gold bar that had the same mass as the crown. If the crown was gold it would displace the same amount of water as the gold bar. It did not; it displaced an amount of water equal to the silver bar. The crown was not pure gold.

16. Did you alter the penny and truly change it into gold? 17. Are there any tests that we could perform on our penny to confirm or deny that it consists of pure gold? 18. Is it a simple task to change one element into another? Why do you think this? 19. What do you know about the structure of the atom that would support your answer to the above question? 20. How might we change one element into another?