I have been trying to make muratic acid from salt and phosphoric acid (didn't know that it's made at 150 °C). After waiting a few days, a third of the time it was sealed by placing a container over it, I wanted to check if some HCl was created, by adding peroxide and etching a small PCB, after 2 days I noticed small white crystals and the solution turned green.

What are those crystals and why is the fluid green?


Likely the green solution contains copper(II) phosphate, $\ce{Cu3(PO4)2}$. "It is commonly encountered as the hydrated species Cu2(PO4)OH, which is green."

Try crystallizing it!

Libethenite, from Wikipedia

Libethenite, $\ce{Cu3(PO4)2}$, crystals.

You have $\ce{H+}$, $\ce{Na+}$, $\ce{Cu+}$ and/or $\ce{Cu++}$, $\ce{OH-}$, $\ce{Cl-}$ and $\ce{PO4{^-}{^3}}$ in solution. You could identify the white crystals by color (white, so probably no Cu in them) shape, birefringence, and solubility; they might be $\ce{NaCl}$ or $\ce{Na3PO4}$. The less soluble should crystallize first, of course.

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  • $\begingroup$ You almost certainly mean Cu++ (not Cu+++) in the last paragraph. Tried editing it myself but the change is too few characters ... $\endgroup$ – Ian Bush Jul 9 '18 at 17:28
  • $\begingroup$ @IanBush, thanks for catching that typo! Cu(III) is unlikely in that mixture, though it does exist in some rare compounds. $\endgroup$ – DrMoishe Pippik Jul 9 '18 at 20:21

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