What is the molar mass of acetaminophen, C8H9NO2?
A. 43 g/mol
B. 76 g/mol
C. 151 g/mol
D. 162 g/mol
E. 125 g/mol
The Correct Answer and Explanation is:
The correct answer is: D. 162 g/mol
Explanation:
To determine the molar mass of acetaminophen (C₈H₉NO₂), you need to sum the molar masses of each atom in the molecular formula. Here’s a step-by-step calculation using the atomic masses of each element:
| Element | Number of Atoms | Atomic Mass (g/mol) | Total Contribution (g/mol) |
|---|---|---|---|
| Carbon (C) | 8 | 12.01 | 8 × 12.01 = 96.08 |
| Hydrogen (H) | 9 | 1.008 | 9 × 1.008 = 9.072 |
| Nitrogen (N) | 1 | 14.01 | 1 × 14.01 = 14.01 |
| Oxygen (O) | 2 | 16.00 | 2 × 16.00 = 32.00 |
| Total = 151.16 g/mol |
Wait — that total seems to be 151.16 g/mol, which might suggest answer C (151 g/mol). But let’s double-check our numbers with a bit more precision and compare again:
- Carbon (C): 12.01 × 8 = 96.08 g/mol
- Hydrogen (H): 1.008 × 9 = 9.072 g/mol
- Nitrogen (N): 14.01 × 1 = 14.01 g/mol
- Oxygen (O): 16.00 × 2 = 32.00 g/mol
- Total = 96.08 + 9.072 + 14.01 + 32.00 = 151.162 g/mol
Thus, the correct molar mass of acetaminophen is approximately 151.16 g/mol, which rounds to 151 g/mol.
So, the correct answer is actually:
✅ C. 151 g/mol
Key Concepts:
- Molar mass is the mass of one mole of a substance and is calculated by adding together the atomic masses of all atoms in a molecule.
- Atomic masses (in g/mol) are taken from the periodic table:
- C = 12.01
- H = 1.008
- N = 14.01
- O = 16.00
- Acetaminophen (also known as paracetamol) is a common over-the-counter pain reliever and fever reducer.
By using correct atomic masses and accurate arithmetic, we see the most precise and correct answer is C. 151 g/mol.