Sciencemadness Discussion Board

Dissolving unreactive metals in diluted sulfuric acid

azpcpXX - 4-3-2016 at 00:53

My chemistry teacher said that copper and another unreactive metal can be dissolved in diluted sulfuric acid. She says that if you pass oxygen thrŠ¾ugh diluted sulfuric acid it will become very reactive and can react with copper without heating. I looked for more information about that but i wasnt able to find anything. Do anyone knows more?

gsd - 4-3-2016 at 00:57

I don't know about reaction happening without heating, but it will certainly happen.

In fact even dilute acetic acid reacts with copper in presence of air but it needs reflux temperature. (about 100 Deg C)


azpcpXX - 4-3-2016 at 01:13

Do you now about the reaction mechanism, how does oxygen interacts with the hydrogen ions?

gsd - 4-3-2016 at 01:50

I guess oxygen converts surface layer of copper into cupric oxide which then reacts with acid to form the salt. The salt gets leached into the solution exposing fresh surface for further oxidation and so on.


[Edited on 4-3-2016 by gsd]

woelen - 4-3-2016 at 02:34

This indeed works, but the reaction is slow.

As a test, put some copper piece or wire in a thin layer (a few mm) of dilute sulphuric acid in a petri dish and set aside. Do not cover the dish. Slowly, over the course of days, the copper will dissolve and you get a blue solution. It may be necessary to add water every other day or so, because of evaporation.

Fulmen - 4-3-2016 at 03:24

Another reaction route is Cu0 + Cu2+ = 2Cu+, oxygen can in turn oxidize the Cu+ back to Cu2+.

This reaction is used to leach copper with ammonia and ammonium carbonate to form cupric ammonium carbonate. It's initially very slow, but as the copper concentration increases it speeds up.

woelen - 4-3-2016 at 04:09

This route only works in the presence of suitable coordinating agents for Cu(+). The ion Cu(+) cannot exist in water without suitable coordinating agents. It works well in the presence of chloride ions and in the presence of ammonia. Both easily form complexes with Cu(+).

Copper etching with CuCl2 and HCl is based on this reaction. Cu(2+) and chloride ion oxidize copper(0) to copper(I), which dissolves as CuCl2(-). Oxygen from the air oxidizes the copper(I) to copper(II), and in this process, acid is used as well, hence the need for HCl. The concentration of copper(II) increases in this situation. Acid needs to be replenished every now and then.

ave369 - 4-3-2016 at 04:53

Not only oxygen can do this. Any oxidizer mixed with a non-oxidizing acid lets it react with unreactive metals. Usually, hydrogen peroxide is used, mixed with either dilute sulfuric or hydrochloric acid.