For which compound are the empirical and molecular formulas the same?

The empirical and molecular formulas of a compound are the same when the molecular formula cannot be simplified further. This occurs when the subscripts in the molecular formula have no common divisor other than 1.

Explanation

• Empirical Formula: The simplest whole-number ratio of atoms in a compound.
• Molecular Formula: The actual number of atoms of each element in a molecule of the compound.

If the molecular formula already represents the simplest whole-number ratio, then the empirical and molecular formulas are identical.

Examples

Here are some examples of compounds where the empirical and molecular formulas are the same:

• Water (H₂O): The ratio of hydrogen to oxygen is already in its simplest form (2:1).
• Methane (CH₄): One carbon atom and four hydrogen atoms are already in the simplest ratio (1:4).
• Formaldehyde (CH₂O): While other molecules might share this empirical formula, formaldehyde's molecular formula is CH₂O. It cannot be further reduced.
• Ammonia (NH₃): The ratio of nitrogen to hydrogen is 1:3, which is already the simplest whole number ratio.
• Carbon Dioxide (CO₂): One carbon and two oxygens already represent the simplest ratio (1:2).

In contrast, consider Glucose (C₆H₁₂O₆). The empirical formula is CH₂O because all subscripts are divisible by 6. The molecular and empirical formulas are different in this case.