Percentage Composition Calculator
Calculate the mass percent of each element in a chemical formula.
How to Calculate Percentage Composition
The percent composition of a compound is the percent by mass of each element in the compound. It is calculated by dividing the total mass of an element in the compound by the total molar mass of the compound and multiplying by 100.
% Composition = ( (Number of Atoms of Element × Atomic Weight of Element) / Total Molar Mass of Compound ) × 100
Example: Water (H₂O)
- Atomic Weight of H: 1.008 g/mol
- Atomic Weight of O: 15.999 g/mol
- Molar Mass of H₂O: (2 × 1.008) + 15.999 = 18.015 g/mol
- % H: (2.016 / 18.015) × 100 = 11.19%
- % O: (15.999 / 18.015) × 100 = 88.81%
Quick FAQs
- What does percent composition tell you?
- It tells you the relative mass of each element in a compound, which is essential for determining empirical formulas and verifying the purity of a substance.
- Does the sum always equal 100%?
- Yes, the percentages of all elements in a compound must add up to 100%. Small deviations (e.g., 99.99%) may occur due to rounding.
- Can I use this for complex molecules with parentheses?
- Yes, our calculator correctly parses parentheses and subscripts, such as in Ca3(PO4)2.