Aluminum Carbonate Test

Name: Linda
Status: educator
Grade: 9-12
Location: NC

Question: Can you tell me how to test for the presence of aluminum
carbonate?
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Basically this boils down to two problems:
(1) confirmation of aluminum
(2) confirmation of carbonate

I would suspect that you can confirm carbonate
just by adding an acid in reasonable concentration.
Try 1M HCl (aq), which should
react with a carbonate to form CO_2 and H_2O, and
you will see bubbles:

Al_2(CO_3)_3 + HCl (aq) --> CO2 (g) + H_2O (l) + AlCl_3 (aq)

The resulting solution of AlCl_3 (aq) could then be
tested for the presence of aluminum. I searched the web
and found the following procedure at
http://homepages.ius.edu/DSPURLOC/c121/week5.htm :

"To test for the presence of aluminum a gelatinous
precipitate of Al(OH)_3 is formed when ammonia is added
to the aluminum ion. Upon dissolving the precipitate
with acetic acid and adding cathecol violet, the solution
turns pale blue. You must have the gelatinous precipitate
for aluminum to be present."

Basically, if you add ammonia solution to the AlCl_3 (aq)
that you just made, you should form a "gelatinous precipitate."
That alone should confirm aluminum, but you can doublecheck
if you have acetic acid and cathecol violet at hand.

Good luck!

Dr. Topper
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