Final answer:
The molecular formula is found by calculating the empirical formula from the percent composition, and then determining how many times this empirical formula fits into the molar mass. The empirical formula is C2H5O, and the molecular formula for the compound is C4H10O2 (Option B).
Step-by-step explanation:
To determine the molecular formula of a compound with 53.3% C, 11.2% H, and 35.5% O by mass and a molar mass of approximately 90 g/mol, we first calculate the empirical formula:
- We divide the percent composition of each element by its atomic mass to find the relative number of atoms:
- C: 53.3 g / 12.01 g/mol ≈ 4.44
- H: 11.2 g / 1.008 g/mol ≈ 11.11
- O: 35.5 g / 16.00 g/mol ≈ 2.22
- We then divide each by the smallest number to get whole numbers:
- C: 4.44 / 2.22 ≈ 2
- H: 11.11 / 2.22 ≈ 5
- O: 2.22 / 2.22 ≈ 1
The empirical formula is C2H5O. To find the molecular formula, we divide the molar mass of the compound by the molar mass of the empirical formula:
- Molar mass of C2H5O: (2×12.01) + (5×1.008) + (1×16.00) ≈ 46.08 g/mol
- Then, 90 g/mol / 46.08 g/mol ≈ 1.95, which rounds to 2.
Therefore, the molecular formula is (C2H5O)2 or C4H10O2. The correct answer is B) C4H8O2.