Sciencemadness Discussion Board

White gas from reaction of HCl with impure CuO?

Draeger - 19-4-2020 at 08:39

So, I made some not really pure copper powder a few days ago, and yesterday I roasted it to convert it to copper(II)-oxide. I then wanted to convert the copper(II)-oxide into copper(II)-chloride. Thus, I poured some 32% HCl onto the copper oxide. Then, immediately, a white gas or mist came off. In a panic, since I didn't know what this could be, I simply threw in a bit of baking soda to neutralize it.

Does anyone know what this was?

Bedlasky - 19-4-2020 at 08:46

It is gaseous HCl. Reaction between conc. HCl and CuO is exothermic and some HCl escaped from solution due to it.

Even when you pour some water in to the conc. HCl, there is some gaseous HCl formation.

[Edited on 19-4-2020 by Bedlasky]

Arcaeca - 19-4-2020 at 09:40

That, and 32% is well above the point where HCl fumes, reaction or not. But theoretically the reaction of HCl and CuO is a double displacement reaction that would gives off H2O, some of which would be released as steam if it gets hot enough.

mackolol - 19-4-2020 at 10:51

Hydrochloric acid tends to fume at even lower concentrations and especially during reactions with something.
Yesterday, when I poured crude mother liquor from propiophenone synthesis into hydrochloric acid, it created so big cloud of HCl that it burned my hands and it was technical grade 31%.
Reason why HCl vapors are white, is that the gas is "damp" it contains water vapors maybe even something steam - like in it, which make it appear white.