How this calculation works
The Molar Mass & Percent Composition Calculator determines the molecular weight in grams per mole (g/mol) and the percentage mass contribution of each constituent element based on IUPAC standard atomic weights.
Mathematical formula and logic
Molar Mass = Sum of (Atomic Weight of Element × Number of Atoms in Molecule). Mass % = (Total Element Mass / Molar Mass) × 100.
Worked example
Glucose (C₆H₁₂O₆) has a molar mass of (6 × 12.011) + (12 × 1.008) + (6 × 15.999) = 180.16 g/mol, composed of 40.0% Carbon, 6.7% Hydrogen, and 53.3% Oxygen by mass.
Calculation assumptions
- IUPAC Standard Atomic Weights (C = 12.011, H = 1.008, O = 15.999, N = 14.007, Na = 22.990, Cl = 35.45, S = 32.06, Ca = 40.078).
- Standard terrestrial isotopic abundance ratios.
Frequently asked questions
What is molar mass?
Molar mass is the mass in grams of one mole (6.02214 × 10²³ particles / Avogadro's number) of a chemical element or compound, expressed in g/mol.
How is molecular weight used in stoichiometry?
Molar mass is the fundamental conversion bridge between mass in grams (measured on a lab balance) and moles of reactive molecules used in chemical equations.
What is percent elemental composition?
Percent composition is the percentage by mass of each individual element present in a chemical compound, used in analytical chemistry to determine empirical formulas.
What is the difference between molecular mass and molar mass?
Molecular mass is the mass of a single molecule in unified atomic mass units (u / Da). Molar mass is the mass of 1 mole of molecules in grams per mole (g/mol); both share the identical numerical value.
What is Avogadro's constant?
Avogadro's constant is exactly 6.02214076 × 10²³ elementary entities per mole, defining the SI base unit mole.
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