Question

If the sulfuric acid and potassium hydroxide are in excess, how many grams of anhydrous alum are formed from 22.00 g of Al (s)? This calculated value is the theoretical yield.

Answer 1

Alum is a type of chemical compd usually a hydrated double sulphate salt of Al with general formula

XAl(SO4)2.12H2O , where X is a monovalent cation such as K or NH4. In some industries, alum is used to refer to Al2(SO4)3.nH2O.

2AlAl2(SO4)3

Molar mass of Al= 26.98g/mol , Moles= Mass of solute / Molar mass of solute

Mol mass of Al in 22g of Al= 22/26.98= 0.815 Al  

It will produce 0.815/2 = 0.408 mol Al2(SO4)3

Mol mass Al2(SO4)3= 2atoms of Al= 2x 27(at.mass of Al)= 54g/mol

= 3atoms of S= 3x32(at.mass of S)= 96g/mol

= 12atoms of O= 12x16(at.mass of O)= 192g/mol  

= 54+96+192=342g/mol  

Mass of 0.408 mol Al2(SO4)3= 0.408x 342= 139.53g Al2(SO4)3