Ibuprofen is C13H18O2. Using C = 12.01, H = 1.008 and O = 16.00 amu, what is its molecular mass?

1. One molecule holds 13 carbon atoms, 18 hydrogen atoms and 2 oxygen atoms. 2. Carbon contributes 13 x 12.01 amu = 156.13 amu. 3. Hydrogen contributes 18 x 1.008 amu = 18.144 amu. 4. Oxygen contributes 2 x 16.00 amu = 32.00 amu. 5. Summing gives 156.13 + 18.144 + 32.00 = 206.27 amu. 6. The value 188.13 amu drops the hydrogen contribution, and 174.27 amu drops the oxygen. _Source: OpenStax Chemistry (CC BY 4.0), Ch 3 "Composition of Substances and Solutions", section 3.1 Formula Mass and the Mole Concept_