Name: ______Date: ______Hr:_____
Physical Science – Unit 6
Lab –Alchemy or Alloy
INTRODUCTION:
What possible explanations can you think of to explain observed changes in a substances.
Alchemy may be regarded as the chemistry of Middle Ages. The practice of alchemy became popular around 200 A.D. One of the aims of alchemists was to change ordinary metals into precious metals (gold, silver, etc). They had particular interest in mercury. They considered it a noble metal that could be distilled and separated into other substances such as silver. Although silver was never produced from mercury, distillation was found to be useful in refining crude medicines. Alchemists also contributed to science by studying many of the properties of substances that are now classified as chemical properties. They also invented some pieces of chemical apparatus that are still common in chemical laboratories today.
In this activity, you are going to do a little “alchemy” by changing copper into silver and silver into gold……..But Wait…………………. Is that really what you are doing or is something else occurring?
MATERIALS:
Bunsen burner (teacher table only)
Hot plates at each table
Wire mesh
Evaporating dish
4 pennies
Zinc powder (warning – highly flammable when moist)
3 M NaOH
Crucible tongs
Steel wool
HCl – for zinc disposal
PREP – Place a small amount of Zn in an evaporating dish and cover with 3M NaOH
CAUTION: Zinc powder is flammable when it becomes moist. It is imperative that you follow the instructions of your teacher.
· Each lab group will get an evaporating dish to perform the lab. I will take your evaporating dish and dispose of it properly by disposing it with hydrochloric acid.
Also, you will be heating NaOH in this lab. This can be very dangerous. Be careful and wear goggles at all times.
PROCEDURE:
1. Put on your goggles and KEEP THEM ON!
2. If needed, buff your pennies with steel wool.
3. Obtain an evaporating dish that already has Zn and NaOH (sodium hydroxide) in it.
4. Place the dish on your hot plate & turn to high. We want it to boil.
5. Turn on your Bunsen burner and heat the evaporating dish very gently.
6. Using crucible tongs, place a clean penny into the solution. You may place several in their, as long as they are all laying flatly in the dish.
7. Make sure the penny is completely covered by the solution. If all of the solution evaporates, GET ME IMMEDIATELY and turn heat to low, This cannot happen!!
8. Carefully observe any changes which the penny undergoes.
9. Remove the penny from the solution.
10. IMMEDIATELY PLACE THE PENNY UNDER THE SINK TO WASH ANY EXCESS ZINC - even a little bit of zinc on the paper towel can become flammable.
11. Wash, dry and gently polish the penny with a paper towel.
12. While holding the penny with crucible tongs, heat it for several seconds in the flame.
13. DO NOT TOUCH THE PENNY!!!!! IT IS VERY HOT!
14. Place the penny under the tap again to cool it.
15. DO NOT DUMP OUT ZINC BUT KEEP IT AT YOUR LAB TABLE!
16. You may repeat these steps so that each individual ends up with 2 silver pennies and 2 gold pennies if wanted.
17. Turn off your hot plate.
18. Clean up and begin conclusion questions.
CONCLUSION:
1. What changes did you observe after the penny was bathed in the zinc-sodium hydroxide solution? (describe color)
2. Hypothesize how this color appeared - what element is causing the color?
3. What happened after the penny was heated over the flame? (describe the color)
4. What you actually did in this lab was to create an alloy. Look up the term, alloy, and write its definition.
5. Using “outside references”, determine what alloy you created? (in other words, google “alloy of copper and zinc.”)
6. Do you think the copper and zinc underwent a physical change or a chemical change? Explain.
7. Describe what caused the penny to turn:
a. “Silver”
b. “Gold”