Help!!?
Answer:
It's called Petina in art stores lol.
here you go:
Copper turns green when exposed to air because
it is being bombarded with AIR that isnt pure... in fact it has alot of sulphur compounds within it that are constantly hitting the surface
dont just use air as an example it is weathering in a way. Rain, and air together are a tough thing to defend against.. most copper takes 8-10 years to patina nicely because copper is low on the list of reactive metals. for example. Iron rusts quickly .because it reacts with alot of things quickly.
once the patina is on the copper however..it slows its reactions further. if you go to england or any other country with copper fixings on their churches or buildings you can see they have patina'd nicely...that is because it is known that patina'd copper is more sturdy than the fresh stuff
scientifically, they are oxidizing. which is causing a change in their actual chemical make up
Initially, bare Cu metal atoms react with air to form the pink oxide, cuprite, Cu2O, which has Cu+1 cations. This gradually oxidizes further to the black oxide, tenorite, CuO, with Cu+2 ions. The black sulfide CuS also sometimes forms. In the presence of moisture, the blackish layer slowly reacts with sulfur dioxide and carbon dioxide from the air to eventually form the patina, which is a mixture of 3 minerals:
brochantite, a green, hydrated copper sulfate, Cu4SO4(OH)6
malachite, the green, hydrated copper carbonate Cu2CO3(OH)3
azurite, the blue, hydrated copper carbonate Cu3(CO3)2(OH)2
It is oxidizing and it therefore a chemical change
chemical
chemical....colour change!
chemical because the composition of the metal is changing.
chemical ...oxidation
it is a chemical change because their is a chemical reaction
of copper,moisture,air which causes the green color when it is exposed 2 air
when u expose copper, it gets oxidized , it reacts with oxygen or carbon dioxide to form cupric oxide or cupric carbonate thus giving it a greenish colour
the green part is oxidized copper. CuO
2Cu + O2 => Cu2O
chemical oxidation
Copper becomes dull when exposed to air; on exposure to moist air it gradually converts to the carbonate.
Thus a chemical change takes place.
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