Question

How many moles of ferric alum (NH4)2SO4Fe2(SO4)3 24H2O can be made from the sample of Fe containing 0.0056g of it?

Answer 1

Molar mass of Fe is 56 g mol-1
1 mol of given alum (NH4)SO4.Fe2(SO4)3 . 24H2O contain 2 moles of Fe atoms.
Mass of 2 moles of Fe atom = 56 g mol-1 x 2 = 112 g mol-1
112 g Fe make 1 moles of alum
Therefore 0.0056 g sample of Fe would make = 1 / 112 g x 0.0056​ mol
= 0.5x 10-4 mol