Glucose has formula C₆H₁₂O₆. Using C = 12, H = 1 and O = 16, what is its percentage by mass of carbon?

Explanation

Using the stated rounded atomic masses C = 12, H = 1 and O = 16, glucose has formula mass 6(12) + 12(1) + 6(16) = 180. Carbon contributes 6(12) = 72 of that total. Its mass percentage is (72/180) × 100 = 40%.