[Platinum]

I'm aware of that Cu is not reactive to diluted HCl and diluted H2SO4. I'm thinking of how diluted? In my case, it's supposed to be 1 part water and 1 part HCl (aq), which it's 18% HCl in aq-solution.

By the way, does Cu resists acids better than stainless steel? (I believe so, but not sure).

Thank you!

[Arkcon]

Copper also resists conc. HCl, but a catalytic amount of H₂O₂ will cause a rapid reaction.  Copper can be dissolved in conc. H₂SO₄, if air or oxygen is constantly bubbled through.  And that's the best way to make copper salts from pure copper, for circuit board plating purposes, for example.  Conc. nitric rapidly attacks copper, but you get clouds of the various nitrogen oxide gasses, and those are pretty nasty.

Stainless steel is at least slight corroded by HCl.  Most steels don't hold up well to any halide in acid solutions.  IIRC, stainless steel is pretty resistant to conc. sulfuric, but I could be wrong about how resistant.

You can find all this info easily in Pauling's Chemistry.  They have some good, basic, metallurgy information.  IMHO, metallurgy of the sort that everyone should know.  Lots of times, the kids come up with, "I need a super acid to eat through prison bars instantly, but I have to carry it in an aluminum toothpaste tube."  And I wish they'd start with the basics first.

[Platinum]

Ok, thanks. I agree, everyone should know the basics of metallurgy if they have an enthusiastic interest in chemistry, like me. I have all upper grade school books in chemistry and one 1300 pages book for university. I also have Vogel's book, very well performed book in a really old, strict school style. I haven't found this information until you answered me.

However, many thanks.