Understanding Empirical and Molecular Formulas

Analysis of Substances

• Analyze composition of substances by finding ratio of elements by mass and number of atoms.
• Example: Combustion of unknown hydrocarbon to determine original masses of carbon and hydrogen.

Empirical Formula

• Empirical formula: shows the lowest whole number ratio of elements in a compound.
• Example: If a hydrocarbon has 2 hydrogen atoms for every carbon atom, the empirical formula is CH2.
• Does not specify the exact number of atoms in a molecule.

Molecular Formula

• Molecular formula: lists the actual number of atoms of each element in a molecule.
• Example: Various molecules with empirical formula CH2:
  • C2H4 (2 carbon, 4 hydrogen)
  • C6H12 (6 carbon, 12 hydrogen)
• A molecular formula can have the same empirical formula if it maintains the same element ratio.

Examples and Exercises

• Assign empirical and molecular formulas to compounds.
• Identify compounds where empirical formula equals molecular formula.

Conclusion

• Understanding difference and relationship between empirical and molecular formulas helps in analyzing chemical compositions.