A Level Chemistry OCR Practice Exam

What information does an empirical formula provide?

1. The exact number of atoms of each element in a compound

2. The charges of the atoms in a molecule

3. The simplest whole-number ratio of atoms of each element

4. The three-dimensional structure of the compound

The correct answer is: The simplest whole-number ratio of atoms of each element

An empirical formula is defined as the simplest whole-number ratio of atoms of each element present in a compound. This means it conveys the relative proportions of the different elements that make up the substance without providing specific quantities of each atom involved. For example, the empirical formula for hydrogen peroxide is HO, which indicates a 1:1 ratio of hydrogen to oxygen, rather than specifying that there are two atoms of hydrogen and two atoms of oxygen in the molecular formula (H₂O₂). The other options detail concepts beyond what an empirical formula encompasses. The exact number of atoms of each element corresponds to a molecular formula rather than an empirical one. Charges of atoms are related to oxidation states and not captured in empirical formulas, which focus solely on ratios. Lastly, the three-dimensional structure of a compound is described by its molecular geometry, not by the empirical formula, which does not provide spatial arrangements of atoms.