Question

Calculate the empirical formula of a compound containing 40% carbon, 6.7% hydrogen, and 53.3% oxygen by mass.

• A. \( \mathrm{CH_2O} \)
• B. \( \mathrm{C_2H_4O} \)
• C. \( \mathrm{C_3H_6O_3} \)
• D. \( \mathrm{CH_4O} \)

Hint:

To find empirical formula: 1. Convert % to grams. 2. Divide each by atomic mass. 3. Divide by smallest value to get ratio. 4. Use ratio to get subscripts.

Answer 1

The Correct Option is A

The empirical formula is derived by converting the elemental percentage composition to moles and then simplifying the resulting molar ratio to the lowest whole numbers. The subsequent steps illustrate the empirical formula calculation for a compound comprising 40% carbon, 6.7% hydrogen, and 53.3% oxygen.

1. Convert percentages to mass: Assume a 100 g sample, yielding 40 g of carbon, 6.7 g of hydrogen, and 53.3 g of oxygen.
2. Convert mass to moles:
   • Carbon: \( \frac{40}{12.01} = 3.33 \, \text{moles} \)
   • Hydrogen: \( \frac{6.7}{1.01} = 6.63 \, \text{moles} \)
   • Oxygen: \( \frac{53.3}{16.00} = 3.33 \, \text{moles} \)
3. Determine the simplest molar ratio: Divide each element's molar quantity by the smallest calculated molar value:
   • Carbon: \( \frac{3.33}{3.33} = 1 \)
   • Hydrogen: \( \frac{6.63}{3.33} \approx 2 \)
   • Oxygen: \( \frac{3.33}{3.33} = 1 \)
4. Construct the empirical formula: Based on the derived ratios, the empirical formula is \( \mathrm{CH_2O} \).