Which statement best describes the difference between molecular and empirical formulas?

Which statement best describes the difference between molecular and empirical formulas?

• A. Molecular shows the actual number of atoms; empirical shows the simplest ratio
• B. Empirical shows actual numbers; molecular shows the ratio
• C. Both show the same information
• D. Neither shows bonds

Answer: (A)

Understanding the difference between actual counts and the simplest ratio is what this question tests. The molecular formula shows the exact number of each type of atom in a single molecule. The empirical formula gives the smallest whole-number ratio of atoms present, not the actual counts in the molecule. For example, glucose has a molecular formula of C6H12O6 but an empirical formula of CH2O; the empirical formula is a reduced version of the same composition, while the molecular formula shows the true composition of one molecule. Sometimes these two formulas are the same, such as in water (H2O), but often the molecular formula is a multiple of the empirical formula. Remember, neither formula indicates how atoms are bonded.

Understanding the difference between actual counts and the simplest ratio is what this question tests. The molecular formula shows the exact number of each type of atom in a single molecule. The empirical formula gives the smallest whole-number ratio of atoms present, not the actual counts in the molecule. For example, glucose has a molecular formula of C6H12O6 but an empirical formula of CH2O; the empirical formula is a reduced version of the same composition, while the molecular formula shows the true composition of one molecule. Sometimes these two formulas are the same, such as in water (H2O), but often the molecular formula is a multiple of the empirical formula. Remember, neither formula indicates how atoms are bonded.