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Alchemy: copper into gold

Place your pre-1982 copper penny in an evaporating dish and heat with a mixture that first turns it silver, then suddenly turns it gold when the penny is then heated on a hot plate.

Caution: Wear safety goggles and gloves, do the reaction in the fume hood with the sash down. Note step 10: special disposal

  • Place approximately 5 g of zinc in an evaporating dish.
  • Add enough NaOH solution to cover the zinc and fill the dish about one-third.
  • Place the dish on a hot plate and heat until the solution is near boiling.
  • Prepare a copper penny (pre-1982) by cleaning it thoroughly with a light abrasive (steel wool pads work well).
  • Using crucible tongs or tweezers, place the cleaned penny in the mixture in the dish.
  • Leave the penny in the dish for 3-4 min. You will be able to tell when the silver coating is complete.
  • Remove the penny, rinse it, and blot dry with paper towels. (Do not rub.) Remove particles of zinc.
  • Using crucible tongs or tweezers, place the coated penny on the hot plate. The gold color appears immediately.
  • When the gold color forms, remove the coin, rinse it, and dry it with paper towels.
  • Special disposal procedures: Do not discard the waste zinc in the trash container. When zinc dries, it forms a powder that may spontaneously ignite. Rinse the NaOH-zinc mixture several times with water. Then add the solid to a beaker that contains 200 mL of 1 M H 2 SO 4 size 12{H rSub { size 8{2} } "SO" rSub { size 8{4} } } {} . When all of the solid dissolves, flush the zinc sulfate solution down the drain.

 Example of the calculation of molar mass:

  • Graph the electric current (in amps) on the y-axis against time (in seconds) on the x-axis. The total charge that passed through the electrolysis cell is given by the area beneath this curve. If the current is constant, this area is:

Q = area = I × t size 12{Q="area"=I times t} {}

Calculate this charge in coulombs.

  • Convert the coulombs of charge to mol electrons: 

N =

  The equation for the reduction half-reaction responsible for the plating at the cathode is

Cu 2 + ( aq ) + 2e Cu ( s ) size 12{"Cu" rSup { size 8{2+{}} } \( "aq" \) +"2e" rSup { size 8{ - {}} } rightarrow "Cu" \( s \) } {}

 Use the mol ratios of the preceding balanced equation to calculate the number of moles of Cu plated out:

n ( Cu ) = n/2 size 12{n \( "Cu" \) ="n/2"} {}  

  • Use the initial and final weighings of the copper mesh electrode to calculate the mass of copper plated out:

m(Cu) = m(final)–m(initial)

  • Calculate the molar mass (M) of copper: 

M =

Electrochemistry pre-lab exercise

Hopefully here for the Pre-Lab

Note: In preparing this report you are free to use references and consult with others. However, you may not copy from other students’work (including your laboratory partner) or misrepresent your own data (see honor code).

Name(Print then sign): ___________________________________________________

Lab Day: ___________________Section: ________TA__________________________

This assignment must be completed individually and turned in to your TA at the beginning of lab. You will not be allowed to begin the lab until you have completed this assignment.

1. Write a balanced chemical equation for the electrolysis of molten potassium iodide (KI).



2. An electric current of 0.211 mA passes through an electrolytic cell for 2.00 min. How many moles of electrons have passed through the cell?





3. A voltage drop of 3.412 V is measured across a resistance of 10.51 ohms. How much current is flowing through the resistor?






4. Why is the anode not weighed before electrolysis begins?


Report form: electrochemistry

Hopefully here for the Report Form

Note: In preparing this report you are free to use references and consult with others. However, you may not copy from other students’work (including your laboratory partner) or misrepresent your own data (see honor code).

Name(Print then sign): ___________________________________________________

Lab Day: ___________________Section: ________TA__________________________

Initial mass of cathode ___________________g

Final mass of cathode ___________________g

Mass of copper plated out ___________________g

Time (min) Voltage (V) Current (A)

Show calculations for full credit!

Average Current = (A)

Total charge through cell ______________C

Number of moles e size 12{e rSup { size 8{ - {}} } } {} through cell ______________mol

Molar mass of copper ______________g/mol


1. What is oxidized and what is reduced when electroplating copper?

2. Write the half reactions that occur at the anode and electrode.

3. Why is it important not to touch the cleaned cathode?



4. What is the purpose of KNO 3 size 12{"KNO" rSub { size 8{3} } } {} in this experiment?



5. How would your results for the molar mass of copper be affected if hydrogen gas were also observed at the cathode?



6. What part of this procedure limits the accuracy of the molar mass determination?


Alchemy - copper into gold

  • Is this reaction an oxidation-reduction reaction?



  •  Why did the penny turn "silver"?



  • Why did it turn "gold"?



  • Why did we heat the penny to turn it "gold"? 

Questions & Answers

find the 15th term of the geometric sequince whose first is 18 and last term of 387
Jerwin Reply
I know this work
The given of f(x=x-2. then what is the value of this f(3) 5f(x+1)
virgelyn Reply
hmm well what is the answer
how do they get the third part x = (32)5/4
kinnecy Reply
can someone help me with some logarithmic and exponential equations.
Jeffrey Reply
sure. what is your question?
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I don't understand what the A with approx sign and the boxed x mean
it think it's written 20/(X-6)^2 so it's 20 divided by X-6 squared
I'm not sure why it wrote it the other way
I got X =-6
ok. so take the square root of both sides, now you have plus or minus the square root of 20= x-6
oops. ignore that.
so you not have an equal sign anywhere in the original equation?
is it a question of log
I rally confuse this number And equations too I need exactly help
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Commplementary angles
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what is a good calculator for all algebra; would a Casio fx 260 work with all algebra equations? please name the cheapest, thanks.
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a perfect square v²+2v+_
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Abdirahman Reply
algebra 2 Inequalities:If equation 2 = 0 it is an open set?
Kim Reply
or infinite solutions?
The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
Embra Reply
if |A| not equal to 0 and order of A is n prove that adj (adj A = |A|
Nancy Reply
rolling four fair dice and getting an even number an all four dice
ramon Reply
Kristine 2*2*2=8
Bridget Reply
Differences Between Laspeyres and Paasche Indices
Emedobi Reply
No. 7x -4y is simplified from 4x + (3y + 3x) -7y
Mary Reply
how do you translate this in Algebraic Expressions
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Need to simplify the expresin. 3/7 (x+y)-1/7 (x-1)=
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. After 3 months on a diet, Lisa had lost 12% of her original weight. She lost 21 pounds. What was Lisa's original weight?
Chris Reply
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Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
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what is system testing
what is the application of nanotechnology?
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
anybody can imagine what will be happen after 100 years from now in nano tech world
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
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silver nanoparticles could handle the job?
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I'm interested in Nanotube
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
Ali Reply
the Beer law works very well for dilute solutions but fails for very high concentrations. why?
bamidele Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Gen chem lab. OpenStax CNX. Oct 12, 2009 Download for free at http://cnx.org/content/col10452/1.51
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