January 16, 2021, 04:24:38 AM
Forum Rules: Read This Before Posting

Topic: After dissolving aluminum alloy in NaOH and acidifying, a white floc forms...  (Read 1585 times)

0 Members and 1 Guest are viewing this topic.

Offline javhert

  • Regular Member
  • ***
  • Posts: 14
  • Mole Snacks: +1/-0
Hello, I was looking formward to perform some quick metal analysis from a 0,5 g piece of aluminum alloy which is stated to contain 8 % silicon and copper and iron at 3 %. Since the alloy resists both hydrochloric and nitric acids, I tried to dissolve it using concentrated sodium hydroxide (sodium is not going to be analyzed on the sample) and then return it to a low pH (less than 2) with excess nitric acid to dissolve the remnants.

The sample did dissolve in NaOH quickly, but after adding acid a voluminous foam-like gray solid formed first and after some time, a white precipitate settled. This white precipitate looks a little like flocs, but is impervious to acids. Adding hydrogen peroxide only got some bubble formation from the solid, so it is probably catalizing the decomposition.

I doubt the flocs are aluminum related since those doesn't form at low pH. What compound could it be?

Offline AWK

  • Retired Staff
  • Sr. Member
  • *
  • Posts: 7840
  • Mole Snacks: +544/-92
  • Gender: Male
What about silicon?

Offline Enthalpy

  • Chemist
  • Sr. Member
  • *
  • Posts: 3600
  • Mole Snacks: +295/-57
What kind of alloy is that? A proprietary composition by the company or individual who cast the part? I've never seen 3% Fe in Al. Or are these tenth of %? Nor did I expect an aluminium alloy to resist HCl.

Sponsored Links