To find the molecular formula of the compound, we need to first determine its empirical formula and then use the molar mass to calculate the molecular formula.
Determine the empirical formula:
Assume we have 100g of the compound, then:
Carbon = 79.4g
Hydrogen = 8.9g
Oxygen = 11.7g
Next, we need to convert the masses of each element to moles:
Carbon: 79.4g / 12.01 g/mol = 6.62 mol
Hydrogen: 8.9g / 1.01 g/mol = 8.81 mol
Oxygen: 11.7g / 16.00 g/mol = 0.73 mol
The empirical formula is the simplest whole-number ratio of the atoms, so we need to divide each mole value by the smallest mole value:
Carbon: 6.62 mol / 0.73 mol = 9.06 ≈ 9
Hydrogen: 8.81 mol / 0.73 mol = 12.06 ≈ 12
Oxygen: 0.73 mol / 0.73 mol = 1
The empirical formula is C9H12O.
Calculate the molecular formula:
To calculate the molecular formula, we need to know the molar mass of the empirical formula. The molar mass of C9H12O is:
(9 x 12.01 g/mol) + (12 x 1.01 g/mol) + (1 x 16.00 g/mol) = 136.11 g/mol
We can calculate the ratio of the molar mass of the molecular formula to the molar mass of the empirical formula:
Molecular mass / Empirical mass = 272 g/mol / 136.11 g/mol = 2
This means that the molecular formula is twice the size of the empirical formula, so we can multiply the subscripts of the empirical formula by 2 to get the molecular formula:
C9H12O x 2 = C18H24O2
Therefore, the molecular formula of the compound is C18H24O2.