A compound with formula C2H6O has molar mass 46.08 g/mol. What is the mass percent of carbon?

A compound with formula C2H6O has molar mass 46.08 g/mol. What is the mass percent of carbon?

• A. 39.9%
• B. 63.2%
• C. 45.0%
• D. 52.1%

Answer: (D)

Mass percent composition is the fraction of a compound’s mass contributed by a specific element, expressed as a percentage. For C2H6O there are two carbon atoms, and the atomic mass of carbon is about 12.01 g/mol. The total mass of carbon in one mole of the compound is 2 × 12.01 = 24.02 g. The molar mass of C2H6O is 46.08 g/mol. So the mass percent of carbon is (24.02 / 46.08) × 100% ≈ 0.5213 × 100% ≈ 52.1%.

Mass percent composition is the fraction of a compound’s mass contributed by a specific element, expressed as a percentage. For C2H6O there are two carbon atoms, and the atomic mass of carbon is about 12.01 g/mol. The total mass of carbon in one mole of the compound is 2 × 12.01 = 24.02 g. The molar mass of C2H6O is 46.08 g/mol. So the mass percent of carbon is (24.02 / 46.08) × 100% ≈ 0.5213 × 100% ≈ 52.1%.