Question

A) on a molecular scale, describe how a crystal of alum differs from a crystal of potassium aluminum sulfate.

Answer 1

A) Answer is: potassium aluminium sulfate is crystal with cubic structure, potassium aluminium sulfate dodecahydrate (alum) is hydrate (contains water or its constituent elements).

B) Answer is: molar mass.

M(KAl(SO₄)₂) = 258.192 g/mol; molar mass of anhydrous potassium aluminium sulfate.

M(KAl(SO₄)₂×12H₂O) = 474.37 g/mol; molar mass of potassium aluminium sulfate dodecahydrate.

Answer 2

A. Since the alum has an additional 12H2O, therefore obviously it is a heavier compound.

The hydrated form (alum) has a molar mass of about 474.39, while the anhydrous form has a molar mass of 258.39 only.

I’m not quite sure but I believe that the alum has a monoclinic structure while the anhydrous form has a amorphous structure.

 

B.  In stoichiometric calculations, the main difference would be on the molar masses to be used in computing for moles from grams and vice versa.