What is the molar mass of acetic acid (HC2H3O2)? (NOTE: H = 1.008 amu, C = 12.011 amu, O = 15.999 amu) 120.1 g/mol 30.0 g/mol 58.0 g/mol 60.0 g/mol
The Correct Answer and Explanation is:
Correct Answer: 60.0 g/mol
Explanation:
To calculate the molar mass of a compound, we sum the atomic masses of all the atoms present in its chemical formula. The chemical formula for acetic acid is HC₂H₃O₂, which can also be written as CH₃COOH, reflecting its structure more clearly.
Let’s break down the elements in acetic acid and calculate:
- Hydrogen (H): There are 4 hydrogen atoms (3 from CH₃ and 1 from OH).
- Atomic mass of H = 1.008 amu
- Total for H = 4 × 1.008 = 4.032 g/mol
- Carbon (C): There are 2 carbon atoms.
- Atomic mass of C = 12.011 amu
- Total for C = 2 × 12.011 = 24.022 g/mol
- Oxygen (O): There are 2 oxygen atoms.
- Atomic mass of O = 15.999 amu
- Total for O = 2 × 15.999 = 31.998 g/mol
Total Molar Mass:
Now, we sum all the contributions:Molar Mass=4.032 (H)+24.022 (C)+31.998 (O)=60.052 g/mol\text{Molar Mass} = 4.032 \, (\text{H}) + 24.022 \, (\text{C}) + 31.998 \, (\text{O}) = \mathbf{60.052} \, \text{g/mol}Molar Mass=4.032(H)+24.022(C)+31.998(O)=60.052g/mol
Rounding appropriately to reflect significant figures based on the atomic masses given, we report the molar mass as 60.0 g/mol.
Why This Matters:
Understanding molar mass is crucial in chemistry because it allows us to relate grams of a substance to moles, which is essential for stoichiometric calculations in reactions. In practical terms, if you have 60.0 grams of acetic acid, you have exactly 1 mole, which contains Avogadro’s number (6.022 × 10²³) of molecules. Acetic acid is a key component in vinegar and has applications in both food and industrial chemistry, making accurate calculations of its molar mass important in real-world contexts.
