1. Understand the Basics
* Molecular Formula: The actual number of atoms of each element in a molecule.
* Empirical Formula: The simplest whole-number ratio of atoms in a compound.
* Atomic Mass: The mass of a single atom of an element (found on the periodic table).
2. Identify the Elements
Ethylene glycol is an organic compound containing carbon (C), hydrogen (H), and oxygen (O).
3. Determine the Empirical Formula
* Assume a 100 g sample: This makes it easy to work with percentages.
* Calculate the moles of each element:
* Carbon (C): 38.7% of 100 g = 38.7 g. Divide by the atomic mass of carbon (12.01 g/mol) to get 3.22 mol C.
* Hydrogen (H): 9.7% of 100 g = 9.7 g. Divide by the atomic mass of hydrogen (1.01 g/mol) to get 9.6 mol H.
* Oxygen (O): 51.6% of 100 g = 51.6 g. Divide by the atomic mass of oxygen (16.00 g/mol) to get 3.23 mol O.
* Find the simplest whole-number ratio: Divide each mole value by the smallest value (3.22 mol):
* C: 3.22 / 3.22 = 1
* H: 9.6 / 3.22 = 3
* O: 3.23 / 3.22 = 1
* The empirical formula is CH₃O
4. Calculate the Molecular Formula
* Empirical Formula Mass: CH₃O has a mass of (12.01 + 3(1.01) + 16.00) = 31.04 amu.
* Molecular Formula Mass: Given as 62 amu.
* Ratio of Molecular Mass to Empirical Mass: 62 amu / 31.04 amu ≈ 2
* Multiply the empirical formula by this ratio: (CH₃O)₂ = C₂H₆O₂
Therefore, the molecular formula of ethylene glycol is C₂H₆O₂.
