It is commonly known that placing a dirty old penny in a coke can for several hours will make the penny look shiny, clean, and new. However, what is the chemistry behind this phenomena?
In short, Coke contains some of the strongest acids available. One example of such an acid is phosphoric acid (H3PO4). Due to the phosphoric acid content in a coke, the pH level in a Coke is quite low. This acid reacts with the zinc (Zn) and copper (Cu) of the penny, and dissolves them into the compound copper phosphate (Cu3(PO4)2). This results in a clean looking penny, as the excess zinc and copper from its surface have been reacted with by the phosphoric acid and removed.
I was interested in this topic because Coke is such a common American beverage, yet its acidity and ability to dissolve other compounds is clearly frightening. The question then follows: if coke is able to do this to a penny, what is it doing to our teeth, throats, and stomachs? This question alone raises many fears about the consumption of Coke, and for many terminates its use entirely.
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