Calculate the theoretical yield of alum if 0.200g of Aluminum was reacted with excess KOH and H2SO4?

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1 answer

2Al ==> Al2(SO4)3.K2SO4.24H2O
The above isn't fully balanced but I've balanced the only part that matters.

mols Al = grams/molar mass = approx 0.0074
Using the coefficients in the equation convert mols Al to mols of alum. That's 0.0074 x (1 mol alum/2 mol Al) = 0.0074 x 1/2 = 0.0037
g alum produced = mols alum x molar mass alum.
NOTE: Some write the formula for alum as the above; others write it as half that (that is KAl(SO4)2.12H2O but that will not change the answer you get.)