Best video I've seen on this topic .However, I would have just included zinc, it also forms a white ppt in NaOH ! , its soluble in excess giving colorless solution.
I was heating melted electronic scraps in hcl. Poured in NaOH(aq) and got a black precipitate. I have no idea what it could be. I thought it was iron but it wasn't green or red. I guess I'm going to have to dry it and do a flame test to find out.
