Why does an oxidized copper coin turn bright pink when in hydrochloric acid?

Question

a copper coin when oxidized (dirty and green) turns bright red or pink when put inside hydrochloric acid. WHY?

Answer 1

copper will not react with any acid coz Cu2+ is located below H+ in electrochemical series.

The coin could be an alloy which could contain iron. Iron can be oxidised with by air and produce iron(ii) oxide which is green in colour. This iron(ii) oxide is an base which can react with acid. tats why the dirt able to dissolve in acid. Copper is basically brown in colour. When the dirt have been removed the pink colour could be the shiny brown metal copper.

Answer 2

the acid reacts with the surface of your coin. the copper turns into copper chloride solution, and oxygen into water.

2HCl + CuO --> CuCl2 + H2O

if you put a clean coin into a HCl solution it reacts as well, but there is no oxygen so the hydrogen is released in gas form, and the metal remains the same pink colour.

hope this helps

Answer 3

The coin changes colour as the acid is removing the oxide layer on the outside of the coin.  If you were to cut the coin in half you'd see the same colour on the inner surface that hasn't been exposed to air before.  Unoxidised copper has a reddish pink colour and this is what you are seeing.