Quote:
Originally Posted by TinyRedLeaf
Drop a tarnished coin into a glass of Coke, and leave it to stand overnight. You'll find the coin bright, shiny and new the next morning!
I made that up. But I'm sure it made you want to try and see if it works, no?  |
Coke does remove rust stains in the bathtub, but actually it doesn't work well on coins ; you would have better luck with Brasso.
Nickel and aluminium plated coins form a layer of oxide outside of them when tarnished, and the surface is VERY inert to chemical reactions. You have to use a properly concentrated (usually undiluted) and strong reducing agent, usually something containing iron or hydride ions.
As for the video, the coin is copper plated if I am not wrong. Copper-oxide bonds are nowhere as strong as copper forms a 2+ bond with oxygen 2- ions to have a stabilised metal oxide surface. The acid reduces the copper oxide back to copper and oxide again easily due to the electronegativity of hydrogen ions being higher than that of copper, resulting in the oxygen being donated to the hydrogen by the copper oxide in the chemical reaction.
I seriously doubt it would work on gray coins which are usually plated with nickel or aluminium.
P.S This question is actually from an A Level Chemistry Practical paper before 2008. My teachers accepted organic acids as answers, but it makes the later part of the question more tedious because there are so many f***ing bonds to calculate the energy released, total electronegativity, concentration and no. of mole required.
Theoretically, carbonic acid (present in coke when CO2 bonds with water through the carbonating process) is only strong enough to be highly reactive at pressurised conditions. If coke that do that, we did immediately inflate ourselves as balloons as soon as we drink a can of coke.