A Level Chemistry OCR Practice Exam

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What does the molecular formula represent in a compound?

The total number of molecules in a sample
The purity of the substance
The number of atoms of each element in a molecule
The structural arrangement of atoms

The correct answer is: The number of atoms of each element in a molecule

The molecular formula provides an exact representation of the number of atoms of each element present in a single molecule of a compound. For example, in water (H2O), the molecular formula indicates that there are two hydrogen atoms and one oxygen atom in each molecule. This information is crucial for understanding the composition of the substance, as it reflects the ratios of different elements that make up the compound. While the total number of molecules in a sample, the purity of a substance, or the structural arrangement do provide valuable information, they do not directly convey the elemental composition within each individual molecule. The molecular formula strictly focuses on the types and numbers of atoms that are present, thus serving as a foundational aspect of chemical understanding and stoichiometry.