Final answer:
The molecular mass of propanoic acid, an isomer of methyl ethanoate, is 74.09 amu, calculated by the sum of atomic masses of carbon, hydrogen, and oxygen in its molecular formula, C3H6O2.
Step-by-step explanation:
To calculate the molecular mass of propanoic acid, an isomer of methyl ethanoate, we need to first understand that isomers are compounds with the same molecular formula but different structures, and hence, the same molecular mass. Propanoic acid's molecular formula is C3H6O2. Using the atomic masses of carbon (12.01 amu), hydrogen (1.01 amu), and oxygen (16.00 amu), we calculate the molecular mass as follows:
(3 × 12.01 amu) + (6 × 1.01 amu) + (2 × 16.00 amu) = 36.03 amu + 6.06 amu + 32.00 amu = 74.09 amu
Therefore, the molecular mass of propanoic acid is 74.09 amu.