Percent Composition Calculator

Two-Element Compound

Calculate percent composition of a binary compound

Element 1 Name

Total Mass of Element 1 in Formula (g/mol)

Element 2 Name

Total Mass of Element 2 in Formula (g/mol)

Three-Element Compound

Element 1 Total Mass (g/mol)

Element 1

Element 2 Total Mass (g/mol)

Element 2

Element 3 Total Mass (g/mol)

Element 3

From Experimental Mass

Calculate percent composition from lab measurements

Total Sample Mass (g)

Mass of Element in Sample (g)

Formula

% element = (mass of element in formula / molar mass) × 100

Frequently Asked Questions

What is percent composition?

Percent composition is the percentage by mass of each element in a compound. It is calculated as: % element = (total mass of element in formula / molar mass of compound) × 100. All percentages must sum to 100%.

How do I find percent composition of water (H2O)?

H2O molar mass = 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%.

What is percent composition used for?

Percent composition is used to verify the purity of a compound, determine empirical formulas from experimental data, and calculate the mass of a specific element in a given mass of compound.

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