Metal finishing Q&As since 1989

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Cleaning Copper

I am doing a science experiment on Cleaning Copper(pennies). I have found information that states if you mix together orange juice and salt, lemon juice and salt, or vinegar [in bulk on eBay or Amazon] and salt, it will remove the copper oxide from the surface of the penny. I am now searching for information on what is in these substances that dissolves the copper oxide.

Amanda Heigns
- Marion, Iowa
 

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I am surprised to hear that orange juice plus salt would make an effective copper cleaner, but I haven't tried that one (I've tried the other two many times). I'm not so sure that even your chemistry teacher FULLY understands what makes lemon juice with salt or vinegar with salt an effective cleaner (I don't). But both lemon juice (citric acid) and vinegar (acetic acid) provide mild acids that provide dissolution power for copper oxides, roughly per this equation.

(2H+)(anion--) + Cu++0-- => H20 + (Cu++)(anion--)

The exact role of the chloride ion from the salt is where things get muddy. I believe it provides additional conductivity to assist in ion transport, and the good solubility of copper chloride probably assists as well.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

Well, I haven't used salt of any kind or orange juice, but I have used rice vinegar, lemon juice, and alcohol. My results were more disappointing than had it been normal vinegar that I was using.

Jacqueline Luo
- Houston, Texas