Question

Two substances have the same molecular and empirical formulas. Does this mean that they must be the same compound?

Short answer

Yes, if two substances have the same molecular and empirical formulas, they must be the same compound. This is because they have the same exact number of atoms of each element, and those elements are present in the same proportions.

Step-by-step solution

Understanding Molecular Formulas

A molecular formula represents the actual number of atoms of each element in a molecule of a compound. It provides the exact composition of the molecule, without any simplification.

Understanding Empirical Formulas

An empirical formula represents the smallest whole number ratio of the atoms of each element present in a compound. It is derived by reducing the molecular formula to its most simplified form.

Relationship between Molecular and Empirical Formulas

In some cases, the molecular formula is the same as the empirical formula, but this is not always true. The molecular formula can be a whole number multiple of the empirical formula. For example, the empirical formula of hydrogen peroxide (H₂O₂) is HO, while the molecular formula is H₂O₂.

Answering the question

If two substances have the same molecular and empirical formulas, it means they have the same exact composition of elements and their simplest whole number ratio is also the same. Since both substances have the same exact number of atoms of each element, and those elements are present in the same proportions, it means the substances are indeed the same compound. The answer: Yes, if two substances have the same molecular and empirical formulas, they must be the same compound.