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Molar Mass, Molecular Weight and Elemental Composition Calculator


Molar mass of O2 is 31.99880 ± 0.00060 g/mol
Compound name is oxygen

Convert between O2 weight and moles
CompoundMolesWeight, g
O2

Elemental composition of O2
ElementSymbolAtomic weightAtomsMass percent
OxygenO15.99942100.0000

Mass percent compositionAtomic percent composition

Sample reactions for O2
EquationReaction type
C3H8 + O2 = CO2 + H2Ocombustion
C2H6 + O2 = CO2 + H2Ocombustion
CH4 + O2 = CO2 + H2Ocombustion
H2 + O2 = H2Osynthesis
C8H18 + O2 = CO2 + H2Ocombustion

Formula in Hill system is O2

Computing molar mass (molar weight)

To calculate molar mass of a chemical compound enter its formula and click 'Compute'. In chemical formula you may use:
  • Any chemical element. Capitalize the first letter in chemical symbol and use lower case for the remaining letters: Ca, Fe, Mg, Mn, S, O, H, C, N, Na, K, Cl, Al.
  • Functional groups: D, Ph, Me, Et, Bu, AcAc, For, Ts, Tos, Bz, TMS, tBu, Bzl, Bn, Dmg
  • parantesis () or brackets [].
  • Common compound names.
Examples of molar mass computations: NaCl, Ca(OH)2, K4[Fe(CN)6], CuSO4*5H2O, water, nitric acid, potassium permanganate, ethanol, fructose.

Molar mass calculator also displays common compound name, Hill formula, elemental composition, mass percent composition, atomic percent compositions and allows to convert from weight to number of moles and vice versa.

Computing molecular weight (molecular mass)

To calculate molecular weight of a chemical compound enter it's formula, specify its isotope mass number after each element in square brackets.
Examples of molecular weight computations: C[14]O[16]2, S[34]O[16]2.

Definitions of molecular mass, molecular weight, molar mass and molar weight

  • Molecular mass (molecular weight) is the mass of one molecule of a substance and is expressed in the unified atomic mass units (u). (1 u is equal to 1/12 the mass of one atom of carbon-12)
  • Molar mass (molar weight) is the mass of one mole of a substance and is expressed in g/mol.
Weights of atoms and isotopes are from NIST article.

Related: Molecular weights of amino acids
molecular weights calculated today
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