To determine the molecular formula of diacetyl, we need to calculate the empirical formula first and then find the molecular formula using additional information about the molar mass.
Step 1: Calculating the Empirical Formula
To find the empirical formula, we need to determine the simplest whole number ratio between the elements present (C, H, and O) in the compound.
1. Convert the mass percentages into grams:
C: 55.8% of 0.30 grams = 0.558 g
H: 7.03% of 0.30 grams = 0.02109 g
O: 37.17% of 0.30 grams = 0.11151 g
2. Convert the grams of each element to moles by using their respective molar masses:
C: moles = grams / molar mass = 0.558 g / 12.01 g/mol = 0.04648 mol
H: moles = grams / molar mass = 0.02109 g / 1.008 g/mol = 0.02092 mol
O: moles = grams / molar mass = 0.11151 g / 16.00 g/mol = 0.00697 mol
3. Divide the number of moles of each element by the smallest number of moles to find the simplest ratio:
C: 0.04648 / 0.00697 = approximately 6.66
H: 0.02092 / 0.00697 = approximately 3.00
O: 0.00697 / 0.00697 = 1.00
Based on these calculations, the empirical formula is C6H3O.
Step 2: Finding the Molecular Formula
To find the molecular formula, we need additional information about the molar mass of the compound.
1. Determine the molar mass of the empirical formula:
C: 6 (atoms) × 12.01 (g/mol) = 72.06 g/mol
H: 3 (atoms) × 1.008 (g/mol) = 3.024 g/mol
O: 1 (atom) × 16.00 (g/mol) = 16.00 g/mol
The molar mass of the empirical formula (C6H3O) is 91.08 g/mol.
2. Divide the molar mass of the compound (91.08 g/mol) by the molar mass of the empirical formula to find the molecular formula ratio:
Molar mass of compound / Molar mass of empirical formula = 91.08 g/mol / 91.08 g/mol = 1
Since the ratio is 1, the empirical formula (C6H3O) is already the molecular formula of diacetyl.
Therefore, the molecular formula of diacetyl is C6H3O.