If the molecular formula is a multiple of the empirical formula, what is true?

• A. The empirical formula is a multiple of the molecular formula
• B. The molecular formula is a multiple of the empirical formula
• C. They are unrelated
• D. They are identical

Answer: (B)

When a molecule’s molecular formula is a multiple of its empirical formula, it means the actual molecule is built from several identical empirical units. The empirical formula gives the simplest whole-number ratio of atoms in the compound, and the molecular formula shows the exact counts. If the molecular formula is a multiple, you can obtain it by multiplying the empirical formula by an integer. That integer is how many times the basic unit repeats in the molecule. For example, an empirical formula of CH2O can lead to a molecular formula of C6H12O6 if you multiply each element count by 6. This relationship holds in general; if the multiplier is 1, the two formulas are identical. The other statements don’t fit because the empirical formula cannot be a multiple of the molecular formula (that would imply fractional or smaller-than-empirical atom counts), and “unrelated” isn’t correct since the two are connected by a simple integer multiple.