Question

determine the mass of oxygen in a 7.20-g sample of al₂(so₄)₃. express your answer in grams of oxygen to three significant figures. part c determine the mass of iron in 79.2 g of fe₂o₃. express your answer in grams of iron to three significant figures.

Explanation:

Step1: Calculate molar mass of Al₂(SO₄)₃

Molar mass = 2×27 + 3×(32 + 4×16) = 54 + 3×96 = 342 g/mol
Mass of O in 1 mol: 12×16 = 192 g

Step2: Find mass of O in 7.20 g sample

Mass of O = 7.20 g × (192/342) ≈ 4.04 g

Step3: Calculate molar mass of Fe₂O₃

Molar mass = 2×55.85 + 3×16 = 111.7 + 48 = 159.7 g/mol
Mass of Fe in 1 mol: 2×55.85 = 111.7 g

Step4: Find mass of Fe in 79.2 g sample

Mass of Fe = 79.2 g × (111.7/159.7) ≈ 55.4 g

Answer:

4.04 g O
55.4 g Fe