How to Calculate Percent Composition by Mass
Determine elemental mass percentages for any chemical compound:
Enter Formula
Type standard chemical formula (case sensitive: e.g. H2SO4, NaCl).
Compute Molar Mass
Calculate total molar mass of 1 mole of the compound.
Sum Element Mass
Multiply atomic weight of each element by its stoichiometric subscript.
Divide & Multiply
Divide element total mass by compound molar mass and multiply by 100%.
Key Features & Stoichiometric Principles
Polyatomic Ion Parentheses Support
Parses complex nested formulas like Ca(NO3)2, Al2(SO4)3, Fe2(CO3)3.
NIST IUPAC Atomic Weights
Utilizes official high-precision standard atomic weights for all elements.
Mass Percent Table & Ratios
Displays mass contribution (g/mol) and mass percentage for each element.
Stoichiometry Guide: Elemental Mass Percent Composition
The percent composition by mass of a chemical compound expresses the percentage contribution of each constituent element to the total mass of the molecule or formula unit.
Mass percent analysis is vital in analytical chemistry for verifying synthesized chemical purities and deriving empirical formulas from elemental combustion analysis.
Frequently Asked Questions
?Should elemental mass percentages always sum to 100%?
Yes, by Law of Conservation of Mass, the sum of individual elemental mass percentages in any pure chemical compound must equal 100.00%.