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?


1 Answer 1


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.

  • $\begingroup$ 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, 2018 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. $\endgroup$ Jul 9, 2018 at 20:21

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.