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When a formula is being determined from measured element masses, why must each mass first be converted to moles?
ABecause atoms of different elements have identical masses
BBecause a formula gives relative numbers of atoms, not masses
CBecause molar amounts are easier to measure than masses are
DBecause percentages cannot be computed from masses directly
Answer & Solution
Correct answer: B. Because a formula gives relative numbers of atoms, not masses
1. Formula subscripts count atoms, so a formula records relative numbers of atoms rather than their masses.
2. Dividing each element mass by its molar mass turns a mass into a count of atoms in moles.
3. Those molar amounts can then be put into a whole number ratio to give the subscripts.
4. Masses alone mislead because atoms of different elements weigh different amounts, not identical ones.
_Source: OpenStax Chemistry (CC BY 4.0), Ch 3 "Composition of Substances and Solutions", section 3.2 Determining Empirical and Molecular Formulas_
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