We did a lab to separate iron from aluminum ore. Here is some specifics on it th

Question

We did a lab to separate iron from aluminum ore. Here is some specifics on it that will help answer my question which is at the end... Background: In this experiment you will be given a mixture of Al(OH)3 and Fe2O3. You're job will be to separate out most of the iron by solution in KOH and then to remove the rest by crystallization of alum, which is KAl(SO4)2 • 12H2O. Procedure: weigh out on a platform balance 4.0g of the Al(OH)3 - Fe2O3 mixture (75% Al(OH)3 by weight). Place in a 200 mL beaker, and add 15 mL of water followed by 25 mL of 2 M KOH. Heat nearly to boiling while stirring constantly, keeping the mixture hot for 5 minutes so that the Al(OH)3 dissolves. Then filter and add 30 mL of sulfuric acid plus 3mL excess to supress hydrolysis of Al3+ to the filtrate in a small beaker.Tie a short piece of thread to a wooden splint and suspend the thread in the solution, loosely cover with aluminum foil until the next lab period QUESTION: Why are some reasons that my crystals did not form?

Explanation / Answer

There's literally a hundred of things that can go wrong in a lab practice, so first of all, don't be dissapointed if you didn't get the result.

I'd also have to know everything you did, not only the instructions but how you did it in real life. I assume that Al+3 (which get's into the solution when you dissolve Al(OH)3 in water) got hydrolyzed before it reacted with the H2SO4. Aluminum ions hydrolyze, and this continues until the cationic charge has run out. The beginning of the hydrolysis reaction is as follows:

Al3+(aq) + 6H2O(l) <-> [Al(H2O)6]3+ (aq)

Why? Well, maybe you have to control very good the dissolution process. If you over-stir (beyond dissolution) Al+3 may begin to reaction with the water. That's why you had to filter right after dissolution and then add the H2SO4 right away.

Hope this helps!

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