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The Chemistry Behind Cleaning Pennies

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by

Jackson Wiegers

on 13 May 2014

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Transcript of The Chemistry Behind Cleaning Pennies

Penny Tarnishing
Pennies become dull and discolored as they age.
Positive atoms from the copper and negative atoms from the oxygen are attracted to each other.
Copper atoms react with oxygen to form copper oxide.
2 Cu + O2 = 2 CuO
The Penny at a Glance

97% copper, 2.5% zinc, and 0.5% tin.
Material consists of separate atoms of copper, tin and zinc.
Copper atoms are key.
Acids and Bases
If you put a molecule into water and it breaks down and releases an H+ (hydrogen) ion, the solution is acidic.
When a hydroxide ion is released, the solution is basic.
Vinegar in water; the molecule (CH3COOH) splits into (CH3COO-) and (H+).
'Dissociated’
What Bases and Acids Make
Form a salt and water.

CuO + HCl ---> CuCl2 + H2O
copper(II) oxide + hydrochloric acid ---> copper(II) chloride
and water.
The pH Scale
Used to measure how acidic or basic a liquid is.
Focuses on concentrations of hydrogen ions (H+) and hydroxide ions (OH-).
Measures values from 0 to 14.
The Solution
Solution of vinegar and table salt .
Leave dull, oxidized pennies in the solution for 5 minutes and their colors and shininess are restored.
But how?
A Look at the Cleaning Solution
Vinegar: (CH3COOH).
Table salt: (NaCl)
When combined, a reaction occurs between the acetic acid and the ions of the sodium and chlorine from the salt.
CH3COOH + NaCl ---> HCl + NaCH3COO
(vinegar) + (salt) ---> (hydrochloric acid) + (sodium acetate)
The Chemistry Behind Cleaning Pennies
How Does This Clean Pennies?
Hydrochloric acid dissolves the copper compound, copper oxide, cleaning the pennies.
Product is copper (II) chloride and water.
CuO + HCl ---> CuCl2 + H2O
copper(II) oxide + hydrochloric acid ---> copper(II) chloride and water.

Things to Consider
Rinsing the pennies when they come out of the salt/vinegar solution is important.
Malachite has potential to form otherwise.
Other Ways To Clean Pennies?
Other acids have the same effect as the salt/vinegar solution.
Water cannot clean them because copper (II) oxide is insoluble in water.
Lemon juice, orange juice, coke, or any acid based ingredient.
Full transcript