When are an empirical formula and a molecular formula the same?
A)always
B)when the mass of the empirical formula unit is equal to the molecular mass
C)when the mass percentages of all of the elements in the two formulas are the same
D)never
E)when the molecular mass is an integer multiple of formula unit mass

Question

Quizplus · Accepted Answer

The empirical formula is the simplest whole number ratio of atoms in a compound, while the molecular formula gives the exact number of atoms of each element in a molecule. The molecular formula can be a multiple of the empirical formula, but they will be the same if the molecular formula mass is a multiple of the empirical formula unit mass. Therefore, when the mass of the empirical formula unit is equal to the molecular mass (which is an integer multiple of the empirical formula mass), the empirical formula and the molecular formula will be the same.

When Are an Empirical Formula and a Molecular Formula the Same