Question: how to calculate the mass percent composition of sulfur in al2(so4)3?
Answer: % by mass = mass of componenttotal mass × 100 %
Mass of 2 Al atoms = 2 Al atoms × 26.98u1Al atom = 53.96 u.
Mass of 3 S atoms = 3 S atoms × 32.06u1S atom = 96.18 u.
Mass of 12 O atoms = 12 O atoms × 16.00u1O atom = 192.0 u.
% of Al = mass of Altotal mass × 100 % = 53.96u342.1u × 100 % =15.77 %