Chem Lab: Synthesis of Alum Question!?

Question

Hi everyone, I am working on my the synthesis of alum. And now I am just not so sure of the fact that if in the process, we don't cut the aluminum sample into small pieces, but rather left it as one large piece; then will this oversight affect the % yield of alum afterwards? My opinion is that it won't affect the % yield of alum at all. And could anyone know about this stuff please help me out! I need an accurate answer! I'm seriously working on this lab. And please also tell me why it won't affect the % yield of alum, of if it does affect, will the % yield of alum be too high or too low? Thank you very much!

Answer 1

Alum is aluminum sulfate. Aluminum reacts with sulfuric acid to produce alum. While the reaction is faster with smaller pieces of aluminum (more surface area to react act), the yield will not be affected as long as there is sufficient sulfuric acid to complete the reaction (even then, the shape and size of the aluminum would not have an appreciable effect).

If you reallllllly want to get into the most picky detail, the aluminum oxide surface layer may not react with the acid, thus favoring the larger piece, which has less oxide on it. This would be an issue only for the most tedious and ridiculous big-time research. If you are asking this question, then this is certainly not an issue for your synthesis, although raising the issue might get you extra points.

So basically it won't affect the yield to the extent you could possibly measure due to the fact that it *all* reacts.

There are a few other things that affect yield such as how well you crystallize the prepared alum and wash the reaction vessel, etc. This has nothing to do with the size of the chunck.

Good luck. This is an easy lab, don't stress out too much. Your yield, like everyone else's will probably suck.

Answer 2

It won't affect the total yield at all, because you haven't changed the amount of metal. What it will change is the rate of the reaction - if that was important. If you want a slow reaction, then you leave it as one large piece.

Answer 3

A student said that once drying the aspirin for a week in his drawer, the aspirin crystals recognized to be dry, although the clear out paper became nevertheless damp. Does the damp paper influence the theoretical yield, the surely yield and the calculated % yield?