There is more than one kind of alum and I don't know the details of the experiment you conducted. Alums, by definition, are composed of the sulfates of a monovalent and a trivalent metal and usually containing a specific number of moles of hydration. A possible reason for adding the H2SO4 could be to form th sulfate part of the molecule. Here is a site that talks more about alums.
http://en.wikipedia.org/wiki/Alum
I conducted the synthesis of an Alum experiment in my lab last week and I'm working on my report. I'm almost done expect I don't know how one could increase the yield of the product (alum crystal)? And also what is the point of adding sulfuric acid? Can anyone help me out?
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In my experiment we produced KAl(SO4)2.12H2O
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