Determine the mass of oxygen in a 7.20 g sample of Al2 (SO4) 3.

Given:

7.20 g sample of Al2 (SO4) 3

Required:

Mass of oxygen

Solution:

Since you are not given a chemical reaction, just base your solution to the chemical formula given.

Molar mass of Al2 (SO4) 3 = 342.15 g/mol

7.20 g Al2 (SO4) 3 (1 mol/342.15g) (3mol O/2 mol Al) (1 mol O2/1/2 mol O2) (32g O2/1mol O2) = 4.04 g O2

Molar mass of Al2 (SO4) 3 = 342.15 g/mol

Molar Mass of O = 16g

in Al2 (SO4) 3 the mass of O2 = 16 x 7 = 112g

342.15 g : 112g

7.20g : X

X = 2.36 g of Oxygen