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ChemistryGeneral Chemistry

ALEKS Stoichiometry Answer: Empirical Formula from Percent Composition

A 100 g basis gives about 3.57 mol C and 3.58 mol O. Their smallest whole-number ratio is 1:1, so the empirical formula is CO.

Question

Measurements show that an unknown compound X has the following composition by mass:

Composition by mass

Carbon42.9%
Oxygen57.2%

Write the empirical chemical formula of X. Show the conversion from mass percentages to moles and reduce the mole ratio to the smallest whole numbers. Use appropriate significant figures.

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Evidence boundary

The calculation assumes the sample contains only carbon and oxygen and that the reported percentages are rounded measurements. Their total is 100.1%, a 0.1-percentage-point rounding difference that does not change the 1:1 mole ratio. The result is an empirical formula only; a molecular formula would require molar-mass data.