Re: what acids in soda do to metal

Well, nearly all soda is acidic.  Luckily most pop cans these days are made 
from aluminum, which in not corroded by the pop inside (in most cases, 
anyway.  If a crack is started when the can freezes and expands, for 
example, the acid can concentrate in that tiny crack and begin a hole.) 
Aluminum does oxidize, but the oxide is not porous, and protects the metal 
from further oxidation.  Anodization, the color "coating" on aluminum is 
simply aluminum oxide. 

Steel is not immune to rust.  When pop used to come in steel cans, the 
inside was coated with tin, a very expensive metal by comparison, to 
protect it from corrosion, and also to avoid that "metallic taste".  

The problem with steel, actually iron, is that the oxide is porous, and 
does not protect the metal under it fdrom further corrosion.  This oxide 
has 3 forms Fe3O4, Fe2O3 ans FeO, each having more oxygen than the previous 
one.  Your nail is steel, and will be corroded in pop.

Try putting a penny, preferably an old one with higher copper content, in 
pop.  It will come out all shiny, becaue=se the copper oxide will be 
removed!  Or, if your mom has pots with copper bottoms, the pop, or even 
catsup will make it shiny.