A compound contains 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. What is the empirical formula ratio of carbon to hydrogen to oxygen in this compound?

• A. 2 : 1 : 2
• B. 1 : 2 : 1
• C. 1 : 1 : 2
• D. 2 : 2 : 1

Answer: (B)

Verified step by step guidance

1. Assume you have 100 grams of the compound, so the mass of each element corresponds directly to the given percentages: 40.0 g of carbon, 6.7 g of hydrogen, and 53.3 g of oxygen.
2. Convert the mass of each element to moles by dividing by their respective atomic masses: use 12.01 g/mol for carbon, 1.008 g/mol for hydrogen, and 16.00 g/mol for oxygen. The formulas are: \(\text{moles C} = \frac{40.0}{12.01}\), \(\text{moles H} = \frac{6.7}{1.008}\), \(\text{moles O} = \frac{53.3}{16.00}\).
3. Determine the simplest whole number mole ratio by dividing each mole value by the smallest number of moles calculated among the three elements.
4. If any of the ratios are not close to whole numbers, multiply all ratios by the smallest integer that converts them into whole numbers (e.g., 1.5 would be multiplied by 2 to get 3).
5. Write the empirical formula using the whole number mole ratios as subscripts for carbon, hydrogen, and oxygen respectively.