Chemistry Regents Practice Test

Given two formulas representing the same compound: Formula A CH3 and Formula B C2H6, which statement describes these formulas?

1. Both formulas are empirical

2. Both formulas are molecular

3. Formula A is empirical, and formula B is molecular

4. Formula A is molecular, and formula B is empirical

The correct answer is: Formula A is empirical, and formula B is molecular

The correct choice points out that Formula A (CH3) is an empirical formula, while Formula B (C2H6) is a molecular formula. An empirical formula represents the simplest whole-number ratio of atoms in a compound. In this case, CH3 indicates that there is one carbon atom for every three hydrogen atoms, which is the simplest ratio of these atoms present in the molecule. On the other hand, a molecular formula provides the actual number of atoms of each element in a molecule. C2H6 indicates that there are two carbon atoms and six hydrogen atoms in the compound, which reflects the actual composition of the molecule rather than the simplest ratio. By understanding the definitions and distinguishing features of empirical and molecular formulas, it becomes clear why this choice is valid — one formula simplifies the ratio while the other provides the exact count of atoms in the compound.