The molecular formula for a compound with a percent composition of 38.7% C, 9.76% H, 51.5% O, and a molar mass of 62.0 g/mol is C₂H₆O₂.
What is a molecular formula?
A molecular formula is a chemical formula indicating the kinds and number of atoms of each kind in a molecule of a compound.
To determine the molecular formula, we need to follow a series of steps.
- Step 1. Divide the percentage of each element by its molar mass.
C: 38.7/12.01 = 3.22
H: 9.76/1.01 = 9.66
O: 51.5/16.00 = 3.22
- Step 2. Divide all the numbers by the smallest one, i.e. 3.22.
C: 3.22/3.22 = 1
H: 9.76/3.22 = 3
O: 3.22/3.22 = 1
The empirical formula is CH₃O and its molar mass is 31.04 g/mol.
- Step 3. Determine the molecular formula.
First, we will calculate how many times the empirical formula is contained in the molecular formula by dividing their molar masses.
n = (62.0 g/mol) / (31.04 g/mol) = 2
The molecular formula is 2 times the empirical formula, that is, C₂H₆O₂.
The molecular formula for a compound with a percent composition of 38.7% C, 9.76% H, 51.5% O, and a molar mass of 62.0 g/mol is C₂H₆O₂.
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