Acetaminophen is C8H9NO2. Using C = 12.01, H = 1.008, N = 14.007 and O = 16.00 amu, what is its molecular mass?

1. The formula gives 8 carbon atoms, 9 hydrogen atoms, 1 nitrogen atom and 2 oxygen atoms. 2. Carbon contributes 8 x 12.01 amu = 96.08 amu. 3. Hydrogen contributes 9 x 1.008 amu = 9.072 amu. 4. Nitrogen contributes 1 x 14.007 amu = 14.007 amu. 5. Oxygen contributes 2 x 16.00 amu = 32.00 amu. 6. The sum is 96.08 + 9.072 + 14.007 + 32.00 = 151.16 amu. 7. The value 137.15 amu is the trap for anyone who forgets the single nitrogen atom. 8. The value 119.15 amu leaves out the two oxygen atoms, and 165.17 amu counts nitrogen twice. _Source: OpenStax Chemistry (CC BY 4.0), Ch 3 "Composition of Substances and Solutions", section 3.1 Formula Mass and the Mole Concept_