Percent Composition
Definition
The percentage by mass of each element in a chemical compound. Calculated as (element mass in 1 mol / molar mass of compound) × 100.
Why is Percent Composition Important?
Percent Composition is an essential chemistry concept used in laboratories, pharmaceutical development, environmental science, and industrial processes. Understanding this concept is critical for accurate chemical calculations, safe laboratory practices, and optimizing reactions.
Our chemistry calculators provide instant, accurate results for complex conversions and calculations, making lab work more efficient and reducing the risk of errors in critical measurements.
What is Percent Composition?
Percent composition is the percentage by mass of each element in a chemical compound. It tells you what fraction of a compound's total mass comes from each constituent element.
Formula
% Element = (Number of atoms × atomic mass of element / molar mass of compound) × 100
Example: Water (H₂O)
| Element | Atoms | Atomic Mass | Subtotal | % Composition |
|---|---|---|---|---|
| H | 2 | 1.008 | 2.016 | (2.016/18.015) × 100 = 11.19% |
| O | 1 | 16.00 | 16.00 | (16.00/18.015) × 100 = 88.81% |
| Total | 100.00% | |||
More Examples
| Compound | Formula | % C | % H | % O | % Other |
|---|---|---|---|---|---|
| Carbon dioxide | CO₂ | 27.3% | — | 72.7% | — |
| Glucose | C₆H₁₂O₆ | 40.0% | 6.7% | 53.3% | — |
| Ethanol | C₂H₅OH | 52.1% | 13.1% | 34.7% | — |
| Table salt | NaCl | — | — | — | Na 39.3%, Cl 60.7% |