Percent Composition Calculator
Percent Composition (%)
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Total Mass Contribution (g/mol)
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How to Calculate Percent Composition
Percent composition tells you the percentage by mass that each element contributes to a compound: % = (n × atomic mass of element / molar mass of compound) × 100, where n is the number of atoms of that element in the formula.
For example, in H₂SO₄ (sulfuric acid, M = 98.079 g/mol), sulfur (S, 32.066 g/mol, 1 atom) contributes: (1 × 32.066 / 98.079) × 100 = 32.69%. Repeat for each element to verify they sum to 100%.
Percent composition is used in analytical chemistry, determining empirical formulas from experimental data, assessing nutritional content, and quality control in manufacturing. It helps verify the purity of compounds and identify unknown substances.
Frequently Asked Questions
What is percent composition?
The percentage by mass of each element in a compound. For NaCl: Na = (23/58.44) × 100 = 39.34%, Cl = (35.45/58.44) × 100 = 60.66%.
How do you find percent composition?
% = (number of atoms × atomic mass of element / molar mass of compound) × 100. Calculate for each element separately.
Should percent compositions add up to 100%?
Yes. The sum of all element percentages in a compound should equal 100% (minor rounding differences may occur).
What is the difference between empirical and percent composition?
Percent composition gives mass percentages. Empirical formula gives the simplest whole-number ratio of atoms. You can derive one from the other.