How many grams of oxygen are in 5.21 grams of Al2(SO4)3?

Answer 1

Use dimensional analysis:

Required information:

molar mass Al₂(SO₄)₃ = 342 g/mol

number moles of oxygen (O) per mole Al₂(SO₄)₃ = 12

atomic mass of O = 16 g/mol

Dimensional analysis:

5.21 g Al₂(SO₄)₃ x 1 mol Al₂(SO₄)₃ / 342 g x 12 mol O / mol Al₂(SO₄)₃ x 16 g O / mol O = 2.92 g O

Done another way using % composition:

1 mol Al₂(SO₄)₃ = 342 g

mass of O in 1 mol = 12 O x 16 g/O = 192 g

% O by mass = 192 g / 342 g = 56.1% oxygen

5.21 g Al₂(SO₄)₃ x 0.561 = 2.92 g of oxygen