Final answer:
The empirical formula mass of a compound with 37.5% carbon, 12.5% hydrogen, and 50% oxygen is closest to 30 g/mol, corresponding to the empirical formula CH4O.
Step-by-step explanation:
To determine the empirical formula mass of an organic compound with the given percent composition of 37.5% carbon, 12.5% hydrogen, and the remaining being oxygen, we first assume a sample of 100 grams. This simplifies percentage to gram conversion: 37.5 grams of carbon (C), 12.5 grams of hydrogen (H), and 50 grams of oxygen (O), since oxygen makes up the remaining.
Next, we convert these masses to moles using atomic masses (C = 12.01 g/mol, H = 1.008 g/mol, O = 16.00 g/mol), resulting in:
- C: 37.5 grams ÷ 12.01 g/mol = 3.123 moles
- H: 12.5 grams ÷ 1.008 g/mol = 12.401 moles
- O: 50 grams ÷ 16.00 g/mol = 3.125 moles
After finding the mole ratios, we divide each by the smallest number of moles to obtain the simplest whole number ratio: 3.123/3.123 = 1 (C), 12.401/3.123 = 4 (H), and 3.125/3.123 = 1 (O), resulting in the empirical formula CH4O.
Finally, to find the empirical formula mass, we add up the atomic masses for each atom in the formula: (12.01 × 1) + (1.008 × 4) + (16.00 × 1) = 12.01 + 4.032 + 16.00 = 32.042 g/mol.
The closest answer to 32.042 g/mol is 30 g/mol, so the answer is (a) 30.