Eugenol, a chemical substance with the flavor of cloves, consists of 73.19% C, 19.49% O and 7.37% H. What is its empirical formula and molecular formula?
The Correct Answer and Explanation is :
Solution
1. Determine the empirical formula
The given percentages are:
- Carbon (C): 73.19%
- Oxygen (O): 19.49%
- Hydrogen (H): 7.37%
Assume a 100 g sample for simplicity:
- ( \text{Mass of C} = 73.19 \, \text{g} )
- ( \text{Mass of O} = 19.49 \, \text{g} )
- ( \text{Mass of H} = 7.37 \, \text{g} )
Convert masses to moles by dividing by atomic masses:
- ( \text{Moles of C} = \frac{73.19}{12.01} = 6.09 )
- ( \text{Moles of O} = \frac{19.49}{16.00} = 1.22 )
- ( \text{Moles of H} = \frac{7.37}{1.008} = 7.31 )
Divide each value by the smallest number of moles (1.22):
- ( \text{C:} \frac{6.09}{1.22} \approx 5.0 )
- ( \text{O:} \frac{1.22}{1.22} = 1.0 )
- ( \text{H:} \frac{7.31}{1.22} \approx 6.0 )
Thus, the empirical formula is C(_5)H(_6)O.
2. Determine the molecular formula
The molar mass of eugenol is approximately ( 164 \, \text{g/mol} ) (typically determined experimentally).
Calculate the molar mass of the empirical formula:
- ( \text{Molar mass of C}_5\text{H}_6\text{O} = (5 \times 12.01) + (6 \times 1.008) + (1 \times 16.00) = 82.14 \, \text{g/mol} ).
Find the ratio of the molecular formula to the empirical formula:
- ( \frac{\text{Molecular formula mass}}{\text{Empirical formula mass}} = \frac{164}{82.14} \approx 2 ).
Multiply the empirical formula by 2:
- Molecular formula = C(_{10})H(_{12})O(_2).
Explanation (300 words)
Eugenol, the chemical compound responsible for the characteristic aroma of cloves, has its composition analyzed to determine its formula. To derive the empirical formula, percentages are converted to masses based on a hypothetical 100 g sample. This simplifies the calculation, as percentages directly correspond to grams.
Next, the mass of each element is divided by its respective atomic mass to find the number of moles. The smallest mole value is used to normalize the ratios. If necessary, the resulting ratios are scaled to the nearest whole numbers to establish the simplest ratio of atoms, yielding the empirical formula.
To find the molecular formula, the molar mass of eugenol, determined experimentally, is compared to the molar mass of the empirical formula. The ratio between the two masses determines the multiplication factor for the empirical formula, providing the molecular formula.
This systematic approach ensures accurate representation of eugenol’s structure: C(_{10})H(_{12})O(_2), crucial for understanding its chemical behavior and applications in flavorings and fragrances.