How to Calculate Percent Composition
What is Percent Composition?
Percent composition by mass expresses the percentage of each element in a compound relative to the compound's total molar mass. It is used to confirm compound identity and to calculate empirical formulas.
Step-by-Step Guide
- 1Calculate the molar mass of the compound
- 2For each element: element mass in formula = atomic mass × subscript
- 3Percent composition = (element mass / total molar mass) × 100%
Worked Examples
Input
H₂O: H=2×1.008=2.016, O=15.999, total=18.015
Result
H: 11.2%, O: 88.8%
2.016/18.015×100=11.19%
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