Disclaimer:
If you are an idiot and don't take proper safety precautions you could die. I will not be responsible for anyone who tries this lab demonstration and becomes ill or causes damage to themselves, to others or to property. If you do cause harm to others, there's a good chance you shouldn't be doing chemistry labs. Now that I think of it... no one should do this lab. I've done a good enough job on this web site to show you all of the important steps. There is no need for you to do this. So don't do this lab!
INTRODUCTION: Realtime video clips showing the transitions
People have tried to make gold from common materials for thousands of years. It seems that people have always wanted something for nothing. That's the theme of this demonstration (or lab depending on your comfort level). We will take a pre-1982 penny and through a few steps, turn it into something that looks like gold.
We will first coat a cleaned copper penny with zinc. This will result in a "silver" looking penny. Next we will heat the penny causing the zinc to bond with the copper to form an alloy we commonly know as brass.
This is a Gary Lorenson lab
SAFETY and CAUTIONS:
The boiling sodium hydroxide (NaOH) used to coat the penny is extremely caustic. Take care to not breath in any fumes from this boiling solution. I recommend that you do this lab in a fume hood. Reduce the heat so that the solution does not boil too vigorously. You don't want hot NaOH splattering your students. Please read disclaimer first
MATERIALS:
1. Goggles and aprons - be sure to be covered and safe!
2. Pennies - Pennies need to be older than 1982. I’ve had success with other years and other countries currency, but < 1982 is generally best.
"The pure copper penny is no longer minted The Lincoln Memorial cent was the last copper penny minted in 1982! After that time the "copper penny" became copper plated zinc with a plating of pure copper. This now makes the "copper penny" approximately 98% zinc. The Lincoln Memorial coin was introduced in 1959 and minted until 1982."
(source: http://www.americaninvest.com/history.html)
This is an interesting point and perhaps has some validity. I've been successful with nearly all dates of pennies as well as Canadian pennies. As with much print/internet material, there is no substitute for experience.
To clean pennies - First we soak them in white vinegar for a while. Next we used steel wool or Scotchbrite pad to buff off the oxidation.
Here is a note from a fellow Science Teacher regarding cleaning. Nice Tip, Thanks Christy!
"To clean our pennies, we use a product called "Bar Keepers Friend". You can purchase it at any WalMart, K-Mart, and some grocery stores. It works great and with very little effort. Bar Keepers Friend is a powder and comes in a gold canister with blue lettering. Good Luck!"
-- Christy from El Paso, Texas
3. Paper towels - lots of them!
4. Tongs - to handle the pennies.
5. Evaporating dish, crucible or beaker - something to hold the NaOH, zinc and pennies. Be sure it's stable on a flat surface.
6. Heat source - I've used bunsen burners but prefer to use a hot plate. A hot plate is much safer and actually easier to use.
7. Sodium hydroxide (NaOH) - You will need about 25 ml of this solution. The concentration is kind of important. I've had best and fastest results with 6M NaOH but 3M works just as well. Anything less than may work but you might have problems. Granular zinc dissolves in NaOH to form [Zn(OH)4]-2. This zincate ion becomes reduced to metallic zinc on the surface of a copper penny.
On October 2, 2002, Bob <robanddandaddy@yahoo.com>,from Decatur High in Decatur, MI.... has a safer solution for this process. He writes:
"By the way, the new edition of the ChemCom book has a revised version using 1M zinc chloride in place of sodium hydroxide. I tried it today and it works great. No more need for a fume hood. There were no bad fumes in the room at all, and the dangers of splattering NaOH were gone as well."
8. Zinc - About 25 grams 20-30 mesh granular zinc works. Something called "zinc powder" is what I use.
On the lab found by Mr. Brown there is a caution that states: "Note: do not use zinc powder, as it may catch fire after contact with water." I don't understand that, and no one else that I have talked to has been able to tell me anything about that. I know that happens to sodium metal and other volatiles *. I've been doing this lab for over 10 years. I have never had/felt/seen/experienced any reaction with the small amounts of zinc powder I use.
* Light Maleski, from Maui, HI, would like to clarify a point here: “...a substance being volatile simply means that it evaporates quickly. The writer is using it in the context that it is reactive to the point of flames and explosions. While I can see where the confusion lies, there is a very distinct and important difference. Volatile compounds evaporate quickly, but if they aren't reactive, they won't explode. For instance, water has a certain volatility to it. It becomes more volatile on hotter surfaces, however, it still doesn't explode or react with anything.”
Here is a caution that I received via email from Shirley Baird: "Zinc powder, when wet will react spontaneously with anything that can be reduced. The zinc is Zn 0 and will go to Zn 2+ if something will take its electrons. Wet zinc powder on paper towel will smolder and generate heat, enough to ignite the paper if it is only damp. Apply friction and you will almost assuredly have a fire."
"Further reading tells me that even when dry the zinc powder may not be safe if it still has base on it. Neutralize the basic coating of the zinc powder by putting 1M H2SO4 on it. When all of the solid dissolves, flush the zinc sulfate solution down the drain. My source is Syummerlin and Ealy, Volume 1 of Chemical Demonstrations, available formt he ACS".
Here is another caution story that I received 01 Oct 02 from "Bob: “I have done the copper into gold lab for 13 years and never had a problem, until last spring. It was 6:30 p.m. and my wife called me at the house I was renovating. She said the fire department was at school, there was a fire in the chem lab, and I had to get there as soon as possible. I got there to find the fire department had put out a fire in the trash container in the lab. Luckily it happened when people were still at the school. Apparently students had wiped down their lab stations and some of the the zinc was on the paper toweling. The chem lab finished about 1:00 p.m. and the paper must have dried sufficiently for the paper to catch fire after 6.
I thought you might like to know about this. I am going to do the lab again tomorrow, but much more carefully.
Bob, Decatur High, Decatur, MI
I have never experienced any of this in the 10 years I've done this lab but it does bear review. It could be that I'm using some kind of "safe" zinc powder, but the label says "Zinc Powder". I don't know what to tell you. You have to decide.
PROCEDURE:
1. Get pre-1983 pennies and clean them to a shine. Try not to gouge them with the cleaning pads...buff them. Be sure they are clean and dry before you go on.
2. Put all of your materials in a fume hood.
3. Set your hot plate at medium to medium high.
4. Place a beaker or dish on the hot plate and warm it up.
5. Put in 25 ml of 6M NaOH (sodium hydroxide), but do it carefully! Try not to get it so hot that it boils.
6. Put in 25 g of zinc in the warmed/hot NaOH.
7. With the tongs, place the penny on the top of the zinc and watch it turn silver! (zinc coated)
8. With tongs, take the silvered penny out and rinse in cold water. Dry the penny.
9. Place the silvered penny on the hot plate surface and watch it turn gold! (brass)
10. Plunge it into cold water dry and you are done!
SOURCES/NOTES:
1. My old college chemistry class about 200 years ago was the first place I did the lab. I loaned my notes out to have them never returned! So:
2. O.K. resource - Internet: http://bellnetweb.brc.tamus.edu/res_grid/cuecmw04.htm/ Link doesn't seem to work so I have a mirror of the exact page here: "Making an Alloy"
3. BEST resource - Internet: http://chemlearn.chem.indiana.edu/demos/THEGOLD1.HTM This is one of many outstanding chemistry demos at this site. An excellent resource and I also have a mirror of the page here: "The Gold Penny"
4. As well as a short lab found by my esteemed colleague here at WHS: Scott Brown.
5. It's important to note that I'm just a Biology teacher stuck with teaching a small bit of chemistry to freshmen.
Modern Alchemy: Turning a penny into GOLD!
(This Gary Lorenson lab found at http://web.mac.com/lorenson/iWeb/LAST/)
Disclaimer:
If you are an idiot and don't take proper safety precautions you could die. I will not be responsible for anyone who tries this lab/demonstration and becomes ill or causes damage to themselves, to others or to property. If you do cause harm to others, there's a good chance you are an idiot and you shouldn't be doing chemistry labs. Now that I think of it... no one should do this lab. I've done a good enough job on this web site to show you all of the important steps. There is no need for you to do this. So don't do this lab!
WOW! If you have read this far, there is a chance that you might actually use my lab. Please drop me an email and let me know how things went. I might add your comments to this lab. Thanks!
